I've had my restored 1961 B40 for just 3 weeks so I'm still getting used to it !
Here's the problem . After starting it ticks over ok but if I 'flip' the throttle, the revs won't settle back down to a normal tick over speed and it 'races'. This has happened during a short ride and I'm sat at traffic lights with a racing tick over. The next set of lights it could be back to normal. Flipping the throttle has no effect.
It's a new (300 miles) Amal 376/253 Monobloc Carb with in-line filter fitted to fuel line. I noticed the throttle was rather 'sticky' so this was removed and mechanism and cable was lightly greased. Both throttle mechanism and throttle cable are new and now feel fine. I removed the throttle slide and checked for any wear marks and gave a light clean. Both needles have been removed and blown through with no dirt apparent. No apparent air leaks from manifold. The float bowl is clean with new gasket fitted.
When running, the engine behaves fine - no misfires etc. It's a b****d to start, especially from warm but i'm still learning the knack ! Not sure if the starting has anything to do with the revs issue.
The only thing that has effect when it's over-revving, is a quarter / half a turn on the throttle stop adjust screw, which then drops the revs back to normal.
Any advice would be very welcome.
Thanks
Sounds like the slide is sticking, but it also reminds me of the symptoms of an air leak on the carb or manifold. I would get the carb on the workbench and have a close look at it. If you need any spares call Hitchcocks, overnight delivery. Not too much wrong there my friend.
Thanks for the reply. A Sticky slide was what prompted me to initially check the same, which looked ok to me.
However, I may have found the cause ! I say May, as until I can thoroughly road test it, I can't be 100% sure.
When I acquired the bike, there was no air filter - just a hole in the battery / tool panel with the moulded fitting for a circular type filter. In a box of supplied bits, I found the metal mesh and retaining clip but no actual filter, so I decided to order the rubber connecting tube between the air intake of the carb and the hole in the battery box purely to try and add more originality. There is not much room to fit the hose so I cut it down to size and managed to squeeze it, sort of in place. The hole and the air intake do not truly align (as someone else on this forum was earlier querying) so I suspect this may have been 'standard' at manufacture. Needless to say, once the shortened rubber hose was in place, it may have been exerting certain pressure against the carb body and it's possible that this pressure may have caused the slide to stick occasionally.
I have now removed the hose, back to how it was and the revs drop back down to normal whilst stationary. Maybe it's my imagination but the bike now seems easier to start (probably my imagination !). The proof will be in the road test later this week I hope. I'll report back !
Good luck with your findings.
I can't see how the pressure from a bit of rubber hose can distort the carb enough o allow the slide to stick.
My carb and tinware hole for the airfilter did not align well at all so I use a bit of fork gaitor of a size that fits the carb flange and compresses against the tinware. It may not give a good airtight seal but I feel it is better than nothing! A lot of carbs were run without an air filter many years ago - in fact my C15 in 1977 never had an air filter and it ran fine on standard jetting as far as I can remember (though I remember going to Amal at Witton in Birmingham where one of the technicians opened up the air slide a little!)
Road test now completed. After first starting and running for a few hundred yards, the revs reverted back to a normal tick-over level when stationary but as the ride progressed, the revs would not return to normal tick over when stopped at lights etc and remained at a uncomfortably high level. So, it's back to square one ! I removed the tank to get access to the carb to remove the slider mechanism and all looks ok with no serious scoring or marks, although in my opinion, it feels like a stronger spring may be required to return the slider back to the top in a more positive manner.
I have no previous experience of the Amal monobloc carb and would be interested to hear from others whether the slider returns quickly or is what I am experiencing, in fact normal. The carb is new'ish with new cables and throttle mechanism. The cables are not held too tightly by nylon ties and are positioned correctly.
I'm happy to remove and disassemble the carb if necessary but would rather avoid it if I can ! Any advice / thoughts gratefully received.
Thanks.
could be that the float height is a little high that would cause the problems you describe but so does worn valve guides and air leaks .
I like to hear an nice "click" when the slide drops down when I release the twist grip when the engine is not running.
When your engine/carb has warmed up, if you switch the engine off does the throttle slide drop down with an audible click? If not it would suggest that it is sticking and possibly causing your erratic idle.
Undoing the twistgrip screws and repositioning it on the handlebars, rotationally, has usually cured any stickiness . My carb. is quite new too, so it is fine.
I expect you have checked the above as part of your trouble shooting, but thought I would mention it anyway!
Thanks for the replies here. I have removed the carb and stripped it down but it all looks very clean with no dirt visible. Re-assembled with new gaskets and O-ring rubber, re-fitted making sure the flange nuts were not overtightened. It re-started just fine and after setting the air and throttle settings, it ticks over very consistent but on twisting the throttle and releasing, it still doesn't feel that the throttle return is as 'sharp' as I think it should be. In saying that, the revs do revert to tick-over speed. All this is in the garage and a further road test is needed. The throttle slide does make a solid 'click' as it hits the bottom but it just seems a bit slow but perhaps I'm being unrealistic and comparing it to my other bike BMW r1150r. which snaps back quickly.
However, whilst playing with the carb it made me think about how this carb actually works, in particular the throttle slide / needle and the integral choke slide. The choke slide puzzled me somewhat as my understanding is that the choke restricts the air supply when cold, enriching the mixture thus improving starting. With the choke lever on the handlebars (RH side) in the 'off' (lever to left) position, the choke slide is actually 'down' in the carb body thus restricting air flow. Moving the choke lever on the bars to the 'On' (lever to the right) position, this then lifts the choke slide thus allowing full air flow.
Perhaps I've been sniffing too much petrol / exhaust fumes recently but I felt very confused !
I searched on line for the correct operation of the choke and ended up speaking to a very helpful person at Burlen (Amal) who informs me that what I thought was 'Off' is actually 'On' and vice-versa. It looks very odd to have the choke lever in the closed or 'Off' position and to have the choke slide restricting air flow and then having the choke control 'open', that is to the right so the inner cable is exposed to the elements etc and this being the 'normal' riding position ! Can anybody here with a B40, confirm what I have been told ? What's the operation on your choke lever ?
So, if what I have been told is correct, I have been running the bike with the choke 'on' all the time !! This might answer the other Rev problem in some way. Now waiting for dry weather until the next road test. More to follow ....
Hi Mike,
Yup! If the last time you saw a choke knob was (like me a few years ago) on the dashboard of some 70's motor from Leyland you would assume that you pull to choke and push when warm.
Just to confuse things more, that is the way that the Amal Mk2 works - but we don't need to bother with such new-fangled devices on our BSAs as I think they were only fitted to the later T140 Bonnevilles.
It does help to think of it as an air slide rather than a choke. Push/release to lower and restrict, pull to raise and open. Sounds like you've been running rich for a while so a good ride out with it open (if it ever stops raining) will hopefully sort things out for you.
Cheers,
Bernie
I remember when I first got my (1965) B40, trying to work out why I had a black sooty plug. It turned out that what I thought was the open setting for the choke was actually closed, and of course vice-versa. I had been using the lever the wrong way round. Took ages, and much discussion on this forum, before I realised one day when I peeped into the carb. Phil.
Quote from: berniej on 14 Nov, 2019, 17:21
Hi Mike,
Yup! If the last time you saw a choke knob was (like me a few years ago) on the dashboard of some 70's motor from Leyland you would assume that you pull to choke and push when warm.
Bernie
not so far back, my A50 chop has a Mikuni fitted with a choke knob.
Thanks all. Yes Bernie, you are about right there ! My sanity is just about restored ! Now I'm really looking forward to a test ride with the choke Off ! (or is it On ??)
Will it sort out the high revving ?? We shall see !
Ahhhhh, really? Choke lever to the right and slider up=choke off and lever to the left and slider down=choke on??? This could explain a lot.....
I am happy with how my air slide operates ie slider up means choke is off, but it seems my handlebar lever works differently to the general rule , and the RR book.
My slide is up, or off, when the lever is fully anti-clockwise and down when the lever is fully clockwise!
That is the opposite of what some people have said.
Or am I misinterpreting what has been written here?
I don't use it anyway, a float tickle is enough for starting, it just seems I have a "backward" lever.
John, it may be a lever that was designed to go on the left of the bars - maybe an advance/retard lever that is now used as a choke lever?
As long as you remember that pull cable = choke off you should be fine!
Cheers,
Bernie
Picture is a zoomed in shot from the original B40 Sales brochure showing the choke lever position.
It looks like the lever is in the Right (clockwise) position, which would now seem to indicate this is the normal running position.
..zoomed in
When cable is slackened the slide will go down and put choke on. When cable is tightened the slide will be pulled up and choke will be off.
Update .. As I now understand the correct position the choke lever should be under normal running circumstances, I took the B40 out for a test ride. To be perfectly honest, I didn't notice much difference in performance. The revs were returning to a normal level for the first mile or so but then ... revs stuck high at traffic lights. It seems to happen when the engine is warmed up. Another issue is the engine was cutting out intermittently (felt like electrical but can't be certain) but righted itself once I eased off the throttle. After stopping the revs wouldn't hold at tick-over at all and a twiddle with the throttle screw was needed. So I decided to take the throttle slide assembly out again to check.
Now for those following this, I have previously mentioned my thoughts about the throttle return spring feeling underpowered and after removing the spring and checking against Amal's website, it appears the spring fitted to my (newish) 376 Monoblock is the 'lightweight' spring and not the 'normal' spring. On speaking to Amal they confirm the lightweight spring is only for use where twin carbs are used. For a single carb, the normal spring should be fitted. So I can only guess that the correct carb was supplied with the wrong spring for a single carb use from new. I have ordered a 'normal' spring. Amal indicate this should solve my 'sticking' problem. I shall see ....
New spring received but is the same as original spring ! Amal say the only difference between the 'normal' and 'lightweight' spring is purely the diameter of the wire 0.040 0.048. The number of coils is now the same - not as their website shows ! So I've now entwined both springs together and fitted them into the carb. This certainly makes the throttle response very quick ! However, after a test ride, no change in the rev problem. I've checked the spark with a Colourtune and it's a even blue colour. Adjusting the throttle stop screw to a normal tickover and then after a few revs the tickover sticks at a higher level. Switching off engine and twisting the throttle, the slide goes down with a positive click. No sticking.
So the next step is again to strip carb, thoroughly clean and blow through, replace all gaskets and hope for the best !
Any additional advice would be gratefully received.
Thanks
Is the advance/retard bob weights returning properly?, assuming your using points ignition
Kev
Thanks for your response here. The distributor was new following a recent full re-build. I've had a look inside and it all looks clean and intact, weights and springs all in place, points gap correct. The bike's been running ok (apart from the high revs).
The Monobloc carb has been removed, dismantled completely (again), thoroughly cleaned with carb cleaner and compressed air, not forgetting the very small holes that are just about visible to me. I have now added a smaller 'inner' spring along with the original throttle slide return spring which gives a satisfactory throttle return feel. The throttle slide does show some signs of marking only very slight in my opinion but the slide returns very positively now.
Started up and set the mixture and throttle stop settings and all seemed well until it warms up and the old problem is still there. The revs do not always return to normal straight away after a twist of the throttle. It takes 2-3 seconds from throttling back to settle back down but as the engine gets warmer this time delay gets worse and in some instances would not settle back at all. The odd thing is that when it's revving high, the throttle stop screw does reduce the revs ok that is, until the next time it's started when it wont tick over !
There are no air leaks at the manifold
All carb components are very clean
The float level has been checked and spot on to the dot on the float chamber cover level.
There is good spring return on the throttle slide.
There is no air filter
The manifold nuts are not overtight.
Using a colourtune, the spark is a decent blue colour at tick over. Not when revving though (goes yellow)
The slide does have some minor marks but moves freely in the body.
With battery cover off and engine revving high, the throttle slide can be seen minutely 'vibrating' within the chamber. Is this normal ? It just takes a touch with a plastic tool to stop the vibrating and then the engine immediately dies.
The engine runs ok when on test rides - no misfires etc
The carb was new in 2016 - only done 300 miles since.
I'm now thinking that maybe there is a problem with the carb body which may be causing this issue. Does anyone have any other thoughts or suggestions ?
if carb slide is loose in the body it will be drawing too much air, what colour is the spark plug?
Is it harder to start when engine is hot?
worn carb can cause these problems.
8)
The spark is Blue'ish when ticking over but turns yellow when revving up. Hot starting can be temperamental but usually starts within 3-4 kicks. Sometimes it just doesn't want to fire and only by opening the throttle fully and kicking over makes it start.
Is it possible that the slide could be faulty or the Jet Block or both ?
have you done a compression test?
have the valve clearances been checked since its been running?
when you get it running spray some easy start or carb cleaner around carb flange to see if any leaks, revs will rise.
are the cables in screw or ferrules into the cap? may be drawing air in.
Compression test done (albeit with a very old pop-up type gauge)
Cold = 65 psi
Hot = 95 psi
Hot with a squirt of engine oil in the cylinder = 105 / 110 psi
Valve clearances Inlet = .20 thou - now a tight .10 thou Exhaust = .20 thou - now .10 thou
No change in revs when carb cleaner / wd40 sprayed around inlet manifold.
Cables are all new. Ferrules into cap with some slack. Cables positioned as vertically as possible into carb.
Original slide return spring with a smaller lighter weight spring fitted inside the original to give a better return feel to the throttle control.
The bike starts a lot better after the valve clearances have been adjusted but still the fault persists. This beings the revs sometimes stick high and won't return to a normal tick over level.
I've noticed when using the colourtune it's impossible to achieve a pure blue spark, best is a blue'ish spark but still with yellow if that makes sense !
When looking into the air intake of carb when ticking over (fast), the slide is vibrating and the lightest of touch of the slide with a plastic tool kills the engine immediately.
What I don't understand is that I can set the tick over quite normally and precisely with the throttle adjust screw, give it a rev or two, the tickover revs then stay high but I can then reduce the revs down with the throttle adjust screw. I don't understand that !
If anyone has any further thoughts then they would be gratefully received.
Thanks for all the comments so far.
Hi Mike I didn't want to believe it at the time but I must have over tightened a carb on my twin and got same symptoms as you I changed the carb and its back to what it should be,you say your carb is new if you still got the old one could you try that (if you have I havn't picked up on it) just a thought Roy
when the bike is ticking over only the pilot circuit is drawing fuel, the slide is not involved.
When you rev the slide rises and allows more air in and fuel via needle jet.
I still think the carb is excessively worn hence the slide is allowing too much air/fuel to pass and when throttle is shut off there is still mixture getting past.
have you got another carb to try?
:)
Thanks for your input.
I've only had the bike for a few weeks now. The previous owner completed a full rebuild over several years. The carb was new in 2016 (I have the receipt) with just over 300 miles on the clock since then. It's unlikely, but possible, that the previous owner may have overtightened the nuts on the carb thus causing some distortion. When I initially removed the carb, the nuts didn't seem excessively tight to me.
It does seem to point to some form of internal wear but after just 300 miles ??
Unfortunately, I don't have access to another carb to try.
Amal say they would be willing to have a look at the carb if I were to take it to them (150 mile round trip for me).
I just want to make sure that I've not overlooked anything else which could possibly cause this problem.
I appreciate your help.
Mike, When you eventually find out the cause, please be sure to tell us. Phil.
Hi there.
I had a same problem on my Starfire. It turned out to be the pilot screw and throttle stop adjustments were wrong.
I found an article on here I think that explained it best. 1st of all get the engine properly warmed up. It seems that yours may have been set when engine not at full temperature and therefore when it is at full temperature it's all out.
start with pilot jet. Fiddle around with it to get engine running as fast as possible. Then throttle stop to slow it back down. Then repeat 3 or 4 times.
Try it. It's simple, doesn't involve dismantling or cost anything. Takes about 10 mins.
It worked for me.
Thanks for all the contributions so far.
After a visit to Hitchcocks, I have now purchased a Anodised Throttle slide for the Monobloc carb which moves much better and more positively than the original slide. They did use a tool to hand 'ream' the inner carb body to ensure it was true.
Before fitting I have, again, removed and disassembled the carb and thoroughly cleaned it out. I'm getting a 'dab-hand' at this now !
The carb flange was slightly distorted (about 15 thou ) and I have rectified this by rubbing down on fine wet n dry on a sheet of glass so it's perfectly flat now. New slide fitted with new flange gasket & spacer, reverted back to the single original throttle slide spring, checked numbers on jets etc (Main is 190, Needle is 106, Pilot is 20, Slide 30, needle is 'C' type and held in mid position 3). Mixture screw 1.5 turns out.
Once refitted, the bike started first time. Throttle screw adjusted, so time for a test ride to get it up to temperature.
Unfortunately, the same symptoms persist. The revs hold high at tick over when at traffic lights etc and occasionally they do drop to normal but it's not instant as I would expect. The one thing I have noticed is when the revs are high when stationary, just letting the clutch out in 1st, just so there is just enough engagement to slowly move the bike a few inches, then pulling the clutch again, the revs then drop to normal and stay there.
Is this indicative of another area of the engine which could be causing this problem ? I would be really interested in any thoughts !
NB: I did check the plug colour after the ride and it was spot on.
Thanks
Have you checked the action of the advance/retard in the distributor as per Kevs earlier post. Make sure the action is smooth and not sticking. Sticking advance/retard could cause revs not to drop back.
Ok. Thanks for the advice.
Will I need to dismantle the unit ? I can see the spring (s) beneath the points but there's not much room to investigate. I have no experience of this type of distributor so any pointers would be really good !
I can't seem to find much on-line about these units and how they function and what the spring / weights actually do and I'm keen to understand this a bit better before I inadvertently do any damage !! (Been there before ...a few times !)
Thanks again.
This may help.
https://www.howacarworks.com/basics/how-engine-timing-works
Regards Mark
Hi Mike,
If you haven't already got a copy, I suggest adding the Rupert Ratio book of BSA singles (engine) to your Christmas list!
This covers just about every process and detail that you will need. Removing the base plate isn't a difficult job and will allow you to check the condition of the springs and for any signs of sticking as Julian mentioned, or wear and tear of the bob-weight mechanism. If there is any slack or stickiness it can result in the bob-weights not being fully pulled in when idling and this will cause the engine to run slightly advanced - and hence at higher revs. Probably worth replacing the springs anyway just to be sure.
While it's out, have a look on the underside of the base plate and see if it has a number stamped - this indicates the amount of advance in degrees. There were a number of variations used across the C15/B40 range of engines and the timing setup varies depending which you have.
Cheers,
Bernie
:) :)
Go for dead simple. Take the petrol cap off. It may be airlocking. Or take the taps out and make sure they are free flowing. If you have already done that then cant think of anything not already posted.
Mike 8)
Mark, a very good article. Now a lot clearer ! Thanks
Berniej. Sent my 'Santa' list off 2 weeks ago. Yes, RR's books were on the list ! Good advice from you - Cheers !
Mike. Petrol cap - Now I wouldn't have thought of that one ! See what you mean though. I'll give it a try.
I'll let you know how I get on ....
Thanks all.
Ive just recieved my new tap for the chop's new tank, the old one was badly corroded on the brass pipe nearly eaten through. Ive re made the tube and fitted, not before drilling out the old broken bit of tube, only to find the two holes that go into the tap area were blocked solid with grey sediment, built up, presumably from the ethanol and corrosion of the brass tube and alloy body.
may be worth checking the complete lines.
I seem to remember weak mixture as a reason for slow return to idle. Maybe a blocked pilot jet or needle is too low? the other thing is the idle screws must be set when the bike is hot. if you set cold it will idle very fast when hot.
Thanks for the responses. I have checked the fuel cap and feed to the carb and all is well. Fuel flows freely so it's back to the Ignition.
Just a recap. The problem is the revs sometimes do not return to a normal tick speed. After much work on the carb I am now looking at the Ignition and in particular, the advance / retard mechanism. The distributor was completely overhauled by the Distributor Doc during the bike's renovation, this included new springs & weights and on first inspection it all looks ok (to me anyway). I decided to have close look and started to remove the points to gain access to the bob weights below and noticed what I think may be an excessive amount of grease (moly ?) which makes me think this may contribute to my problem.
What I don't know is, is this a 'normal' level of greasing. Perhaps the more experienced may care to comment on this and offer any other comments.
I hope to attach 3 pictures (if it doesn't work, I'll post them separately)
Dist 1 shows the unit with lower point removed
Dist 2 shows central cam removed showing weights and grease
Dist 3 shows weights removed
All comments gratefully received !
Thanks
Dist 1
Dist 2
Martin Jay, who is the Distributor Doctor, has been helpful to me via emails quite recently, perhaps drop him a line explaining your situation.
His email address should be on the Distributor Doctor website, I don't have it to hand at the moment.
I dont see the reason for greasing the points assembly at all, in the old days we only ever used to put a drop of 3in1 on the felt pad once a year if we remembered. as I see it, the 'compartment' is oil free but liable to collect dust so excessive grease will attract dust and grit adding to wear and ignition problems
:) :) :)
Something else that I may have missed. Have you tried opening the throttle by simply reaching in and pulling the cable up at the top of the carb. If so did it return to normal revs straight away??? Could be a simple cable problem. May even be something as simple as the carb to not "sitting " exactly square.
Mike 8) 8) 8)
Mike, the mechanism from throttle to carb is all new and the cable works as it should. The slide can always be heard to make a nice returning 'click' so I'm fairly certain it's not a carb problem. I'm really looking for views about the level of grease in the advance / retard mechanism of the distributor as seen in the photos.
I will take up an earlier suggestion to contact the Distributor doc for advice as well. Just for clarification here, the distributor is mounted on top of the crankcase.
Thanks for the responses.
I haven't greased my A/R mechanism, just oiled it. However, if it has been professionally overhauled I'd assume that new springs have been fitted and even if the mechanism is heavily coated I would have thought that the springs should pull the bob-weights fully back in when idling. If in doubt however, wash all the grease off, reassemble with some light oil and give it a whirl.
I have had the same problem since my S90 since rebuild and not yet diagnosed it. I did have a charging problem which would have been affecting the spark so now that's fixed I'll be testing it all again as soon as the weather allows. I'll update if there's any change due to resolving the charging problem.
Cheers,
Bernie
Thanks BernieJ
I will do exactly as you advise as soon as I can.
There is one thing I've only just thought of and it's when I removed the bob weights I noticed some 'scoring' on the underside of the weights. There are, what look like rivet heads, on the body of the distributor underneath the bob weights. I wonder if there's some fouling ? Once it's all clean I will be able to see.
Also, I assume that by removing the points and A/R mechanism, this should not affect the ignition timing.
Will report back once done and tested.
Cheers !
Scoring doesn't sound good and would suggest that there has likely been sticking in the mechanism if parts are fouling.
I haven't been able to find an exploded parts diagram of the distributor but did find this: http://www.brightsparkmagnetos.com/library/Parts%20lists/Lucas%20motor%20cycle%20parts%201936-57/G02-07%20Contact%20breaker%20units%20distributors%20and%20suppressors.pdf (http://www.brightsparkmagnetos.com/library/Parts%20lists/Lucas%20motor%20cycle%20parts%201936-57/G02-07%20Contact%20breaker%20units%20distributors%20and%20suppressors.pdf) which might help.
Is the scoring on the top of the 'shaft and action plate'? If so maybe that suggests either wear in the hinge post/bob-weight interface allowing some downward rocking or possibly missing washers under the bob-weights (I don't know if there are supposed to be any but hopefully someone might know or have a diagram??). Or is it maybe due to the cam rubbing on the top of the plate?
Might be an idea to disassemble, clean and examine the parts for wear and see if the bob-weights have been fouling the plate - or if they can be rocked such that they would.
(We may be moving closer to understanding why BSA, in a blaze of enlightenment realised in around 1966 that perhaps a distributor for a single-cylinder bike (oxymoron?) wasn't the most sensible design option and moved to side-points for the '67 models onwards....)
But we are where we are I guess and have to solve the riddle!!
Cheers,
Bernie
Re sidepoints, to be tiresomely pedantic, at least some BSAs were sidepoints before '67. My B40 is 1965 and is sidepoints. I just mention it as a point of interest. Phil.
By the way, I don't doubt for a second that Bernie is aware of that. Phil.
:) :) :)
Purely as a matter of interest I had a BMW R65 that did exactly what you are experiencing. I NEVER found the cure. I sold it to a guy who was quite happy with the problem and I don't think he ever found the cure either.
Mike 8) 8) 8)
I have now removed the points, condenser, springs, weights and cam plate and de-greased the unit as best as possible without actually removing the distributor from the crankcase.
I mentioned earlier about some 'scoring' on the underside of the weights. It look like the 4 raised rounded areas, as can be seen in the photo, may be the cause but I think they are there to reduce friction for movement of the weights, so it may be normal to see some markings.
The components, in my inexperienced opinion, look in good condition but I have two questions, perhaps silly ones...
1) There is a screw which goes in the top of the rotor shaft, which I thought was there to secure the cam to the shaft, but it does nothing. What is it for as it doesn't secure the cam in any way unless I have a missing part !
2) I have not removed the distributor from the crankcase. Can I assume that the ignition timing will not be affected by what I have done so far ?
Thanks all.
Is the screw there to put a washer under to lock the cam on full advance to set the static timing. I would try to clean more of that grease out and reassemble with a light touch of oil on the moving parts then see how it runs.
Kev
If you measured maximum opening width of the points they should be set the same at reassembly. Any difference will alter the timing to some extent.
There is another way to check if your advance/retard is erratic, by using a strobe.
To set the timing accurately this way you would need a timing disc fixed onto the alternator rotor and a reference mark on the stator (I use typing correction fluid to make a white base and then pencil a line over it) but that's been covered elsewhere on the forum.
However, you wouldn't need a timing disc to check for irregular behaviour, just a pair of reference marks on stator and rotor roughly lining up at TDC.
If you then run without the primary cover on and strobe you should be able to see how the A/R is behaving and if it always returns to the same position at idle by observing how the offset between the two marks varies with engine speed. Might help work out if this is distributor-related or not.
Cheers,
Bernie
The timing will be affected by the points gap on re assembly. Did you measure the gap before dismantling?
Make a mark across the distributor body to the crankcase and undo the clamp screw and pull the distributor and clean it properly. Note which way the offset cam drive comes out or you can put it in 180 degrees out. Check the spindle bushes and wash everything out with paraffin or what ever you prefer and then re oil it if sound. Easier to work on when on the bench. Advance and retard springs do wear and it is difficult to assess if worn. Distributor Doctor supplies new ones but they are very expensive for what they are ( I think about £14 plus postage and plus the twat). Any other components can be supplied by that company.
I refurbished my distributor on my B40 and it made a difference to the tickover and running. To be fair, I have never worried too much about the timing. I set mine with a marked rod before TDC down the piston hole and then fine tune it my turning the distributor after running the bike to give a smooth engine response. I probably run mine slightly retarded as I feel that the settings suggested make my engine feel a little harsh.
Adrian, thanks for your thoughts.
The points were 0.015" before removal and that's what I set them at after re-fitting so I don't understand why the timing should then be out.
To gain access to the distributor clamp screw on my bike involves removing exhaust, gear lever etc and then crankcase as there is no clamp on the outside of the crankcase which would have made life so much easier !
I agree with what you say about the cam drive plate as it can be fitted in 2 ways. The springs are in good condition as are the weights, as the unit was overhauled by the Distributor Dr in 2017 (300 miles ago).
Using the rod in the hole method with both valves open, I have checked the 1/16th BTDC and it looks like the cam is at the position to be just starting to open the points, so that looks ok. The weights pull back nicely if twisted by hand.
However, the only way I can start the bike now is by putting a washer under the spindle screw which clamps the cam and prevents movement. This surely indicates the static timing has changed , but how ?
I'm reluctant to remove the distributor if it's not necessary but would like to understand if and why the timing may have changed ?
Thanks
Following on from my earlier post, I have now 'discovered' a screw / bolt on the outside of the crankcase which, I now realise, is the distributor clamp screw !!!
I never really looked at this screw as I just thought this was another crankcase screw / bolt. Now it all becomes somewhat easier.
With the slightest turn of the distributor the bike now starts and runs. I still don't fully understand how the timing can change by just re-setting the points but hey-ho !
As for the uneven tick over, a road test will answer that in due course.
One question, now I have discovered the distributor clamp screw (cough-cough!) if I need to remove the unit, do I unscrew the screw all the way out or is just loosening it enough to presumably just withdraw the distributor from the case? Is it that easy ?
Thanks
Mike,
We all do daft things or overlook the obvious! I rewired a Bantam and the inline fuse kept on blowing I only got the fuse to not blow when I changed some of the rectifier connections. I then realised I had wired the battery the wrong way! I spent hours trying to find out what was wrong.
Anyway, you don't have to remove the screw - it is an internal clamp that fits into the crankcase. As I said previously, make a careful note of the positioning of the drive cam. I find it easier to mess with the points and set the gap when on the bench and then replace the distributor. It is only the clamp screw and 1 wire to connect.
You may have a bit of a problem getting the distributor to seat back in place. The clearance at the clamp is tight and a bit of careful jiggling may be necessary to reseat it. Yours may go back easily - mine was fiddly.
I'm glad you got the bike running. At tickover, play with the distributor settings by turning it each way slightly to see what it does; you wont do any harm. If you have marked the body you can always return it back to the original position. As I originally said, my bike was always a little harsh at the recommended setting so I retarded it a little and it seems to run better and more smoothly.
Adrian, many thanks for your reply. I think I will remove the distributor at some stage as you suggest as I can see it will make adjusting the points a lot easier. The cam drive shaft in the distributor does seem to have some play but at least the bike runs.
I've noticed that when running, if I twist the distributor slightly in a anticlockwise direction the revs increase and fade in the other direction. Would it be correct to clamp the distributor where the revs are at the highest ? Where this is, the LT voltage wire on the outside of the distributor is very close (1/4") to the engine's cooling fins.
Just waiting for some decent weather for a road test !
Hi Colin,
The revs increase as you advance it and decrease when you retard it - that's quite normal.
However, if you position for maximum revs you will likely be setting it too advanced - the stick down the plug'ole is the simplest way of making sure you're close to the the right setting and then you can tweak a little if you wish (running a bit retarded with unleaded is quite usual).
Due to the way that the drive shaft engages with the driving gear it's possible to reposition the alignment of the body so that the cable exit is where you want it.
You can remove the distributor unit - or just lift until the drive is disengaged - then rotate it and re-insert. The drive is a helical gear arrangement so you can move it round a few teeth to get a better alignment. The shaft will rotate a little as you refit so allow for that.
Cheers,
Bernie
Not sure you can do that Bernie.
If I remember correctly the drive gear stays in the engine - there is a flat piece of metal which is at the end of the distributor shaft which engages into it.
I agree about running slightly retarded with unleaded. I set mine up with the stick down the hole to get an approx. setting and then take the bike for a ride and make slight adjustments to keep the engine smooth but also retain power. If it is too advanced you can get pre ignition and also the engine will appear "harsh". Too retarded and you will loose power and the engine will run a bit hot.
As I previously said, mark the distributor against the crankcases when you initially set the timing and you will have a reference point to go back to and it will also allow you to see how far you have moved the distributor.
By the way, my wire exits towards the rear of the distributor, away from the engine fins.
You're right Adrian - I was forgetting that it's the drive shaft that has the helical gear at the bottom and the distributor shaft engages in the top of that as you say.
To rotate as I was suggesting it would be necessary to lift that and rotate it before re-engaging - which is a bit more of a job to do but when rebuilding it gives you a way to posiiton the distributor so that the lead exits in a suitable direction.
Cheers,
Bernie
Not 100% sure whether my similar problems are carb or ignition related. Before splashing out on a new carb I decided to order the BB electronic ignition kit in order to eliminate most of the distributor-related possible causes. If this has any significant effect I'll update - if not.... it's new carb time!
Cheers,
Bernie
Bernie, I hope the EI kit solves your problem, it certainly has been elusive.
I have a BB EI kit which I have not got round to fitting yet as there have been so many other things to fix first, but I would be grateful if you could give a little feedback on how you get on with yours. Such as, is the spark at the plug any stronger than before fitting it, or any other issues you may have had.
My C15 starts fine at the moment so I am a little wary of making things worse!
Finally, this morning I have been able to take the B40 out for a test ride!
As a recap, the revs intermittently, would not revert back to normal tick over and held at a uncomfortably high level. As a result of my investigations I can now strip and re-build a Monobloc carb in my sleep and having subsequently moved on to the ignition side, as recommended by many contributors, I can now report back with some good news !
Although the distributor had previously been completely overhauled, I was concerned about the presence of a lot of moly grease in the advance/retard mechanism. It just seemed excessive to me and this again, was supported by the views of various contributors. So, after cleaning the grease out, just leaving a light smear on the plates and adding a spot of 3 in 1 to the bob weight pivots I was hoping this would solve the problem. With the Static timing re-set, points at 0.015" it all seemed ok in the garage. The bike now starts easier with 2 or 3 kicks maximum. The test ride would prove it !
Well, I'm happy to report that this sorted it out 100%. The revs now drop back to normal tick over with no hint of hesitance. The bike seems to run better. Hopefully for some time ! So, thanks to all contributors, I got there in the end !
...now let's have a look at that oil leak !! (another post coming up I think !)
Thanks all
Glad you sorted the running problem out!
When you sort out one problem, another one usually raises its ugly head!
The joys of running an old British bike.................