Uneven Revving B40 - Any ideas ?

[AdrianS]

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.

[Crazy Mike]

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 !

[berniej]

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

[AdrianS]

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.

[berniej]

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

[berniej]

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

[johnan]

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!

[Crazy Mike]

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

[AdrianS]

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.................