B34-2 Rebuild

[Goldnrust]

The photo there was of the Fiat clutch against the BSA friction discs just to show how similar they were.

I've attached a couple of photos of my clutch assembly here. It certainly looks 'right', so I presume it might just be  a clutch assembly from a slightly different year BSA?

That's fair enough if I was being a bit optimistic about performance! Either way, I wouldn't expect it to be surging / back firing when ridden at speed os will keep chasing issues. 

There's no disc nut on the end of my magneto armature? Just a normal hex head, which when removed allows me to remove the points cam which is keyed to the magneto shaft. Also yes, that's a modern condenser in there, as it's externally mounted it was a quick easy thing to try swapping out incase that was the root of my weak spark, but sadly made no difference.

I was always dubious of LED lights, but I have to say the latest crop have really improved. I've used www.classiccarleds.co.uk a couple of times now and been impressed. Ultimately my headlight is now as bright as if I'd fitted a 60w Halogen bulb, and yet it draws so little power that the limited output from the Maglita has no problem keeping up.

[Steve.S]

My apologies. Please ignore my comments about your clutch, which is the correct and original clutch. Apart from being a bit thick, the confusion arose because I'm using the Blue star single spring clutch, which is quite different. And I forgot it's me that's using the wrong clutch. Also, the car centre plate confused me, but of course that's the Fiat plate you removed the friction discs from. Sorry about that.
Unfortunately, I can't post pictures. It just says the file is too big and I have no idea how to make them smaller.
Re the headlight, have you been out at night? Which bulb are you using?
I'm using 35 degrees advance, which I find very satisfactory, but I don't know the distance measurement.

[Goldnrust]

haha, not to worry. I could have worded it better and included more pictures to demonstrate how I was making use of the Fiat clutch parts.

Yes I've been out at night and I was quite content with the brightness. As I said, better than my 1970's Suzuki headlight!

I'm using this bulb, with was a direct fit into my reproduction headlight bowl; https://www.classiccarleds.co.uk/products/bpf-p36d-437-368-370-414-led-headlight-upgrade-6-12-and-24-volt-negative-or-positive-earth-great-beam-strength-and-pattern?_pos=1&_sid=9c1304850&_ss=r&variant=39564853379181

I went for the 3000K colour, warmer and softer than some LEDs, but it still isn't quite as warm as a tungsten bulb.

I'm set to the 1/2" of advance specified in the manual, with a plug gap of 0.023" . NowI'm sure I read that somewhere, but I can't for the life of my find where I'd read that as correct! Checking the manual I can see 0.018" listed. So maybe having too large a plug gap isn't helping me.

The bike is back together now, so I'll hopefully get out in the next couple of evenings for some test runs and will report back.

[Steve.S]

Thanks for the LED info. I'll try one.
I 'm sure that 0.023" is too large a gap. It must be a very good Maglita if it starts on that. However, it may be the cause of your problems at higher speeds.
Have you discovered the Advance/Retard Stop? May be worth playing around with?

[Stubaker58]

Just come across your thread.
Really interesting and well done for overcoming all the issues so far!
Thanks for taking the time to post.
Hope you get the misfire sorted before we run out of summer!

[Goldnrust]

Thanks Stubaker58. 

First test ride report; better but not fixed. I've picked up some speed, was hitting ~45mph on the flat, but when heading for high revs its still missing and popping at times.

The bike runs the same with 0.023", 0.018" and 0.015" plug gaps. So I've left it on 0.018" for now.

Back to the drawing board! I think the magneto overhaul has made an improvement, so I'll have another pass through the carb jetting options. The weak spark could have been giving me a false sense of which jets worked best.

The carb is back to standard wit thew needle in the 4th position and the 75 main jet, but obviously fuel is very different now to that from 90 years ago when the bike was made.

If the carb improvements don't help, my next thought is whether the valves are floating due to weak valve springs. It is only right at the top of the rev range the the bike misses. This thought was triggered by reading some other threads on here.

I did fit some NOS outer valve springs when I overhauled the head, as the ones that came on the bike were clearly soft and deformed with age, but I couldn't find any inners. I make take some measurements and see if I can find a modern alternative spring.

[courtney]

Steve is right about performance/speed. Mine will do 45-50mph at a push (that's if my speedo is right), but it's happiest cruising around 30-35mph on back roads. Mine had a fair bit done to it before I got it - re-sleeved, new piston etc., so I think my engine is pretty decent and the magneto was overhauled and recently remagnetised. Nothing has been done with the gearbox as far as I know, but one thing I do need to sort out is the oil pump as the worm is worn. I'm running an old KLG spark plug that's probably as old as the bike, and it works far better than any of the modern replacements I have tried, so I would definitely recommend hunting around for an old Lodge or KLG as the bike will start and run better.

[Goldnrust]

Very late update, but I thought it might be of interest to know that after many unsuccessful attempts to fix the misfire I have finally found and fixed the issue.

It appears the spring on the points had gone soft and was allowing the points to 'float' at higher engine speeds, thus loosing spark and causing the misfire. After a bit of a bend to the spring to give it a bit more tension again, the engine finally feels like it's running 'right', which is a huge relief.

It's not really that much faster mind! But it's good to have found and solved a problem.