Hiya, further to my thread elsewhere about breaking down, I’m checking if my vac advance is working. Giving it a bloomin’ good suck with the dizzy cap off, how far should I see the mechanism move? I can get it to move about 1mm at full human suction (non-smoker, occasional cyclist) . I got the most expensive non-brand Chinese dizzy I could find. Would a lame / limited advance mech cause the bog under load / backfire issue? Grateful for any advice.
I'd expect the points plate to move about 5mm or so at full suction. I've got a video somewhere but its about 8MB so too big to post up.
It should move under mouth suction from end to end.. about 5mm , or 6 degrees of rotation. Could be gunged up . If you strip down the distributor watch out for the little nylon top hat sliders pushed into holes in the top moving plate to act as bearings. These vanish easily .. Some distributors use dimples on the plate.
That’s really helpful mate, thanks. I don’t think it’s too dissimilar to what I’m getting but will check again and compare.
Thanks Mike, very unlikely that I’ll find myself stripping it down. If I can call it, loading the parts cannon, lighting at arm’s length and retiring to a safe distance is my usual go to
If you dont want to strip it down, flush between the moving plate and the fixed plate with carb cleaner until it stops running out brownish, then drizzle with 3 in 1 or sewing machine oil round the moving plate...wipe off excess.
Here’s two still from a video of me operating the vac manually. Doesn’t seem enough to me. I promise they are different- look by the copper wire you can see the difference- just…
The Chinese dissys are prone to this. If you put your glasses on, and look closely at the arm that comes out of the vac can, you will see it rubs on the bottom plate. If you are lucky, you will be able to fix it by loosening the two little screws that hold the vac can on the body, and jiggling it until it clears the plate, and moves freely. If your less lucky, you may end up bending / filing that arm to get clearance. If that doesn’t work, Chuck it over snottys fence. Try and track down an original dissy for trouble free motoring.
I think you could well be onto something there. I’ve slackened the screws on the outside of the dizzy body and fiddled. It does now seem to move a bit more. I can move it further with my finger than suction though. Am I ok to leave the screws half a turn out from where they were previously? Tempting to test drive it, but I might have a pint and look tomorrow… Edit: might just be wishful thinking though actually…
It’s idling really sweetly now. Have driven it around the camp site and seems ok. Will go round the village tomorrow and see does it play up #prayforadvancetiming
Your distributor does look really clean and dry.. maybe a spot of oil might help . A guide to the expected movement of the plate is the length of the raised track under the ball bearing under the domed clip.. Another place to check for things catching is the insulator where the wire comes in may be rubbing. Another thought is that the ball bearing has to roll back and forwards under the black spring clip . If thats sitting up the "wrong" end of the clip it will lock the travel of the advance plate until you firmly manually push the plate back and forwards. Then it will "magically" free up as the ball ends up in the right place. A side effect of being shiny and dry in there..
The vac advance works while cruising on light throttle not when under load. However the centrifugal advance probably isn’t working also. That would cause bogging & lack of power. I had that issue with a cheap Chinese distributor, limped home from the Lake District with it some years ago. It’s now rotting away nicely at the bottom of @snotty s fence. 123 dissy is the way to go
Early morning diagnosis may have occurred. Having a poke around and discovered the rear (front - the one you can’t see) nut on the carb was loose. That would also explain the fuel whiff in the engine bay which I thought was just a result of me brimming it. Tightening it, it wouldn’t nip up so carb off and the stud is unscrewing. Going to try some thread lock stuff when I can get some. Any thoughts on whether that would be sufficient? Edit: loose carb would explain rough running due to being lean yes?
I had to put an M8 bolt through @redgaz carburettor mount when it was loose at Keiths Field... the stud pulled out. Both were loose .. it ran like rubbish except when going flat out and the carburettor sucked down onto the manifold.. Or clean up, degreasing and use a proper epoxy like JB weld or 6hour plus setting epoxy to glue the stud back in.. (faster it sets more it stays soft.) Or a cable tie or mole grips...
I seem to be back on the road. Threadlocker almost worked but didn’t. On my bike to the shop, I passed a guy tinkering with a beetle who also had a splitty on the drive. So I asked him if he had a spare stud or anything. he’s drilled it out, tapped it and put a new helicoil in! Result! carb is on and is like a different vehicle. Smooth acceleration, no hesitation, faith restored people can be amazing hey? thanks all
