I've spent the weekend on my first long rides on my '54 B31 and because I was with other bikeists, I've been able to get more of an idea what is happening and when . . . .
BUT
No one knows just what is causing the problems.
Here's what the bike does and the things I've done to try to fix the problem in past weeks.
Can anyone advise what it could be please?
(I think it's getting too much fuel when it's hot)
Randomly, the bike will splutter and cough, sending a cloud of black smoke from the exhaust as it does this.
Sometimes it will run for 20 miles plus, perfectly but other times it will misbehave as soon as it's warm.
Once it's started the cutting out, it won't re-start easily. I've since worked out that I need to pull the decompression lever in and kick the starter furiously (which results in one massive explosion that shoots flames from the exhaust and then a couple of further "very loud bangs" as I keep pumping the starter.
Once the bangs finish, drop the decompression lever and keep kicking furiously and she will fire up like there's never been a problem (sometimes - other times I need to repeat the explosions).
All the while, there's a strong smell of petrol (she doesn't need a tickle to start from cold and no choke - fired up first kick, just for reference)
Once re-started, I can literally only open the throttle a few mm on the grip before she starts the spluttering and stalling again.
I have to do long clutch-slips to pull away and as the revs pipe, change to 2nd before the over revving causes more spluttering.
If I only use the first few mm of throttle, I can eventually work my way up to 4th gear and if I increase the revs VERY slowly (in any gear) I can pick up speed, though only to about 30mph.
When she is moving along nicely, with minimum throttle, if I twist the grip on to give more speed / fuel, she starts the spluttering and will die UNLESS I throttle off a lot or change to a higher revving gear.
Trying to set off up a hill, even a gentle one, is almost impossible and I'm sure I've almost burned out my clutch.
When riding at a speed that the bike can tolerate, as soon as the extra torque for the hill kicks in, she starts to splutter and die.
I can replicate the condition when we've got going steadily on tiny throttle. If I wind-on it'd throttle, she will cough and splutter as above. Even when doing 45mph in 4th (eventually) if I try to increase the throttle, she will splutter and stall if I don't recover it, by reducing torque and load on the engine.
I've fitted the following but all in vain.
New plug, cap & HT lead. Cleaned points
Stripped the Carb and ultrasonic cleaned it thoroughly.
Cleaned armature & brushes.
Fuel cap breather hole is clear
Float definitely not sticking
Suggestions are: sticking valve, allowing too much fuel past and it's choking / flooding.
I'm at my wit's end with this now. It's so random when it does it and impossible to ride as it is.
Any ideas ed the solution are welcome.
(I'd even thought about borrowing a Carb from someone, to discount that? (Any takers?)
I'd drop the needle a notch and see if that improves it but if it's the carb it is way off.
You really need to pull the plug and look at it when it's playing up and also when it's not. It's a good indicator,of what's going on inside the engine!
Also you said that once the bangs finish you drop the decompression lever and keep kicking. Can you kick it over without using the lever? Or do you just use it to ease it over TDC?
Where do you live? I'm in Cornwall. Would happily pop over and lend you my carb for a day (providing its not adjusted!). I wouldn't post it though.
Quote from: KernowPete on 07 May, 2024, 06:28
I'd drop the needle a notch and see if that improves it but if it's the carb it is way off.
You really need to pull the plug and look at it when it's playing up and also when it's not. It's a good indicator,of what's going on inside the engine!
Also you said that once the bangs finish you drop the decompression lever and keep kicking. Can you kick it over without using the lever? Or do you just use it to ease it over TDC?
Thanks for your reply.
I use the decompression lever to "clear the fuel and get it spinning" by furiously kicking over and over.
Once it's done "banging" I'll drop the lever and can keep kicking whilst I've got the kicking momentum up.
Eventually, it will fire up and I/stop the kicking.
I'll attach a photo of the plug whilst it's playing up.
The trouble though, is that it will run perfectly from cold and can run perfectly for many miles sometimes - so this is a random problem.
Something is randomly changing.
Quote from: KernowPete on 07 May, 2024, 06:45
Where do you live? I'm in Cornwall. Would happily pop over and lend you my carb for a day (providing its not adjusted!). I wouldn't post it though.
Thank you but I'm in Sheffield, South Yorkshire.
I think that borrowing a Carb would be an ideal test but I don't know anyone who has one.
Thank you though
I hope you don't mind me asking but are you using the choke correctly? It should be tight wire for OFF.
You wouldn't be the first person to think it's slack wire off and be running on full choke all the time!
Quote from: Fraz on 07 May, 2024, 07:36
I use the decompression lever to "clear the fuel and get it spinning" by furiously kicking over and over.
Once it's done "banging" I'll drop the lever and can keep kicking whilst I've got the kicking momentum up.
Eventually, it will fire up and I/stop the kicking.
That is a sure sign of a flooded engine with too much fuel in it. Almost certainly a sign of a carburation issue, the plug looks pretty black in your pic. Could there be any chance the float is sticking? As has been said, is the choke off? From your descriptions that doesn't seem to be the issue, if I leave the choke on on my B32 in about ½ a mile it starts to misfire. There is nothing random about it.
So is it flooding because it stops firing or does it stop firing because it's fouling the plug.
Choke on would be the latter,
Carb issue would be the latter,
Maybe an oil issue could be the latter (drain to crankcase blocked?). Never had this but guess it's possible.
Ignition issue would be the former
Does the plug seem oily?
What does the plug like when it's not doing it?
When you've had the problem have you tried changing the plug straight away for a new one?
What Carb are you using..? If it is a Mikuni they can gradually give those symptoms.
The plug does look very black and fouled, either too much fuel or too cold a heat range. Please try a new plug.
B31 is not a very high performance engine, so a standard or mildly hot plug should be OK.
Any news Fraz?