Hello everyone,
I'm new to the forum so a short introduction. I own a Sloper S30-13 which I restored three years ago. After a catastrophic failure of the old piston, I rebuilt the engine again - I redid the main bearing which was already quite worn, new piston, rings and pin, new small end bush, rebore, new valve guides and springs. Amazing - after the rebuild she started on the first kick without complaints.
After an initial running in phase, I have now been doing tuning rides to see how she performs at top speed, but the results were somewhat disappointing. She starts reliably on the first kick and settles in a stable idle, pulls very well, and accelerates up to 70-75km/h without any problems and can cruise at those speeds all day. Beyond that it's a struggle. After a very loooong straight at WOT she eventually reaches 80km/h and tops at about 85km/h. After that there's nothing.
Since there are no signs of an ignition timing problem, I started experimenting with the needle setting on the carburettor. After trying all 5 needle positions, the best performance on mine seems to be on the third notch from the bottom.
However, none of the needle positions made a change on the top speed. To be noted, at this top speed of 85km/h the engine doesn't seem to be struggling or being tortured - it just seems to not be able to increase the rpms beyond that. So now I'm out of ideas and hoping for some pointers from the experts here in the forum.
My gearing is for solo work: engine 21t, g'box 19t and final drive 42t. Timing is set at TDC, fully retarded, fag paper just pulling out of the points. Carburetter is an Amal 6/024. I also double checked that the slider and choke are closing and opening fully, which I can confirm. After warming up, my choke lever can be anywhere between 3/4 and fully opened. If below that, there is a drop in performance, so the mixture also seems to be OK.
The only other "problem" I have since the rebuild is a somewhat large oil leak from the middle of the pushrod covers, where they telescope into each other. There is no seal there as far as I know. Is this a known issue? and if so are there are any known cures?
Cheers,
Gui
Dear Gui,
It seems I'm facing the same trouble ie finding more power or "nervosity".
Can you tell me how many inch (or mm) did you put before TDC, fully retarded?
Maybe it's a question of ratio before g'box and final drive .
br Michel from Belgium
Hi Michel, my S29 runs fine with the timing set to points opening at tdc on full retard. This is what the owners manual recommends. I think that equates to 10.7 mm or 35 degrees before tdc if fully advanced. Cheers, Bevan.
Salut Michel,
My timing is set like Bevan said and what the manual recommends - points opening at TDC and full retard.
My gearing is standard for solo work.
Although I have the right and original carburetter, I found that the jetting and slider were wrong. So I got the right jets and slider for it, but this made no change. My top speed is about 90km/h and that's it. The engine doesn't sound or feel over worked, but she just doesn't go beyond that. I really don't know what could be the reason at the moment.
Gui
Maybe the valve timing is out.
Idie,
That has crossed my mind. The cam gears are meshed with the timing marks all on their right spots. I've wondered though if due to wear the rocker arms are not opening the valves as they should or something like that. The valve springs are new and the valves were reseated with new guides as well.
I quote from the 1929 BSA OHV Sloper handbook:
MAGNETO TIMING
To retime the magneto first remove the magneto gear wheel. Remove contact breaker cover and spark plug. Rotate the engine in the forward direction until the inlet valve closes. Then insert a pencil or rod through the sparking plug hole and move the engine still further until the piston is felt to be at the top of its stroke.
Move the ignition control lever (or twist grip) on the left handlebar to the fully-retarded position and turn the magneto shaft in the correct direction (i.e., clockwise from the contact breaker end) until the platinum points P have opened not more than 3/1000in (test with feeler gauges).
Lightly tighten up the magneto gear wheel and check the timing by finding the top of the compression stroke again and examining the position of the points. If correct finally tighten the magneto gear wheel nut.
Hope this helps.
Further update. 496 CC OHV Sloper 1929/30 should have a top speed of about 70/75 mph. Safe cruising speed 55 mph.
Hi Alan,
Thanks and it's what I followed. I really don't believe the ignition timing is my problem. The Sloper is also not the only British classic motorcycle I restored and run, so I do have some experience. But always good to check because I don't rule out making a mistake somewhere.
My highest ever top speed was 94 km/h which is about 58 mph, and that's at WOT on a long straight after about a mile. She cruises all day at 75-80 km/h without any problems, pulls well and starts hot or cold on the first kick. There just doesn't seem to be any power above 85kph and it's a struggle to get even past 90kph. So, something is not quite right, but I just can't find it.
Here's further information on my sloper:
Carb:
Amal 6/024 1 1/16" with air cleaner canister
New needle 3rd notch from top
New Main jet 160
New 6/4 slider.
New needle jet .106
Gearing:
engine sprocket 21 teeth
Gearbox output sprocket soll 19 teeth
rear wheel chain wheel 42 teeth
Clutch chain wheel 48 teeth
New main bearing rollers
New piston, rings, pin, small end bush and rebore
New valve guides
New valve springs
Valve seats recut and lapped
New clutch plates (doesn't slip nor stick)
Magneto and points refurbished.
:) :) :)
Is the engine perhaps a bit tight after all the new work ???
Mike 8) 8) 8)
Just a thought...does it rev higher in the intermediate gears, there are very cheap tachos on fleabay (less than £20) which enables comparisons to be made, obviously if it revs significantly higher in (say) 3rd than top it could be the gearing that requires attention.
Have you tried a plug chop after a top speed run? That might give an idea of whether there's a mixture problem.
Also, is the float level correct?
Finally, is fuel flowing freely to the carb? I once had a performance issue which turned out to be fuel starvation caused by a lump of fluff in the pipe. It would allow enough fuel through to start and run, but not for fast running. Sounds unlikely, but.......
She doesn't rev higher on lower gears and accelerates well through the range.
I haven't tried a plug chop, but will have to try that one of these days. Same with the float level, although if it's low, I really don't know how to adjust it on this type 6. I have checked the fuel flow and it's free. I might have to adapt a larger fuel hose to see if that makes a difference to my cooper pipe.
Playing with the choke lever doesn't give me any indication that the mixture is weak. When I start shutting the choke the performance goes down.
But do keep sending your suggestion and ideas for me to test. Eventually I'll find something.
It's not really a case of adjusting the float, so much as checking it's OK. Float is not punctured, needle seals on the seat, float is properly clipped to the needle. Just eliminating basic bugs.
A Sloper at WOT will drink at least 110cc of petrol per minute, so that gives a flow rate to aim for.
If the power seems to be rpm limited, could it be the magneto weakening at high revs? I don't know if this can happen, just a thought. Also, I have in the past had a refurbished magneto come back to me with a dodgy armature.
I would also experiment with ignition timing. Even though you have done it by the book, think about advancing it a tad at static. Mark the lever position where it is correct by the book, set to this position, test your top speed, then carefully advance the ignition. If you gain speed that will show that the engine is capable of operating at higher revs and that you don't have a breathing or fuel supply problem.
:) :) :) :)
The only other thing that comes to mind is whether the Mag is actually going to fully advanced. Because less than fully advanced would possibly give the fault that you are experiencing.
Mike 8) 8) 8)
All this is very interesting. It sounds like lack of fuel. When my Velocette Viper did the same thing ,I found that it was ok with both taps on. On investigation I found that there was a poor flow threw both taps. A drill sorted that out. I know you most likely only have one tap but is the flow enough to keep up with the engines demands Also try a larger main jet even if it is out of spec.
At the moment, fuel flow really could be my main suspect. I shall try to set up another petrol tap with a larger diameter fuel line and test it. Perhaps the tap I have or the copper pipe to the carb are too restrictive. Both are not original and the copper pipe I did myself.
Here's a pic of my tap and petrol pipe.
The fuel filter inside the tank could also be clogged. Unbelievably, I once found a tank that was Petsealed with the filter still in place. Before fitting new parts I would just disconnect the copper pipe and measure the flow rate out of the tap.
Have You checked the camlift?
Quote from: Gustafsson on 25 May, 2021, 10:38
Have You checked the camlift?
I haven't. Is there a reference value?
Today I was finally able to do another test run with a larger fuel line. No luck. Still the same.
Next I will try advancing the ignition some more, even though it is set by the book -points just opening at TDC, fully retarded. Running out if ideas here.
Cheers,
Gui
Another test run after advancing the timing a bit. She seemed happy with it and the acceleration was a bit better, but still no change in top speed. Just doesn't go much beyond 80kph or seem to have power at the top end. Since I opened the timing chest to adjust the ignition timing I also rechecked the valve timing just to be sure, and yes, all the markings were lined up properly.
Are all the marks correct. Can you check them with a degree disc or by substitution with other cams. Difficult I know with such an old machine.
So I checked the valve timing today.
The exhaust timing is by the book - opens at 60 deg before BDC and closes at 20 deg after TDC.
The inlet is another matter. It opens at 40 deg before TDC and closes at 75 deg after BDC. It should be 24 deg and 65 deg respectively. So the timing marks are correct but it seems the cam profile is wrong. Perhaps it was reprofiled at some time in the past, but not done correctly. The way it is, the inlet valve is opened too long.
I increased the inlet valve gap and did a test run, but made no difference. Above 80km/h there is not much left.
Last thing to try will be a larger main jet, but I'm losing hope now.
It is a long way out the inlet timing seems that a lot of the charge is going out of the exhaust. I wouldn't have thought increasing the valve clearance would help it might change the timing but you lose the lift. Maybe you can borrow a cam from someone.
Final test today with a larger main jet. Went from a 160 to a 170. Also no difference in the top end.
I may have found the cause for the lack of performance. Following a suggestion to check if the slider was opening all the way (it was) I noticed the jet block made a step on the carb's throat. Disassembled it and sure enough it's a 15/16" jet block and not 1 1/16" as it should be. Further it has a 39 stamped on the top side and a 30 and a 0 on the bottom - not sure what this means. The question now is where can I get a 1 1/16" jet block for a 6/024 Amal? I checked some blocks for later 276's but the holes on the sides are completely different.
When I checked my sons Shooting Star I found the same thing on a monobloc carb. I know it's not original but can you not fit a later 276 carb on as a temporary measure.
I only have spare one inch jet blocks. I have a 1929 557cc SV sloper and the jet block is one inch. I'm attaching photos of a spare jet block and it is difficult to see how the inlet could be increased by 1/16th of an inch without having a larger bodied carburettor which I don't know if it exists. My SV Sloper runs fine on the one inch jet block. Hope this helps a bit.
Thanks Alan, but the 6/024 carb on the Sloper is 1 1/16", so it would have to be a jet block of the same size. If I can't find one I will probably have to find a later 276 carb of that size.
I know it's a long time ago, but you mentioned this post recently in your reply to B31 lack of performance. Sounds like you still have a problem?
You seem to have identified 2 culprits, so were you able to get the correct size jet block and another inlet cam?
Both of these will surely make a difference.
Hi Steve,
I couldn't find the correct jet block for the original carb, but I installed a new 276 Amal. The cam profile was just a suspicion which didn't confirm itself.
The problem remains with the new carb which I am confident to have it properly tuned. It accelerates to about 80km/h and can stay there all day, but it doesn't really go beyond that. I have run out of ideas...
Cheers
Gui
Hello!
New here, but driven my 1028 Sloper about 20 years now.
When I read this thread, I think that problems may be in valve springs. Maybe them needs more pre load?
Loose springs cuts easily top revs.
B.R.
Jari
I have reprinted a number of Pitman Books(//) of the BSA by Waysider 1929. https://bsamanuals.com/product/bsa-1929-waysider/ (https://bsamanuals.com/product/bsa-1929-waysider/) at £17.99
I also have some books where a couple of the photos were a bit grainy nothing major) hence second quality I can sell these at £10 including UK postage.
my e mail and paypal is stevearch58@hotmai.com
The 1926 Flat Tank version of the BSA Waysider book will be available next week at £20 inc UK postage (only 25 printed) these are good quality perfect bound (paperback) book printed in the UK.
Dear BSA friends
I'm looking for two « Valve push rod with ends» ref 24-600(2) for my BSA Sloper (1930) .
Can you help me ?
Thank you in advance.
Michel Deneve
Belgium