engine cutting out when returning to idle

[the_count]

hey everyone,
the mog has developed a rather anoying habbit... after being reved instead of returning to idle, she dips below & often cuts out.
Just wondering if anyone has any suggestions?

I've recently give her new coil, points, rotor arm, condencer, leads, plugs, fuel pump, cleaned out carb

my mate was over with his multimeter & seemed to think the coil wasnt getting / giving enough power when idle... just wondering what would be the cause of this & if it could be the route of my problems?

Also not sure if worth mentioning, but the exhaust seems to have a bad blowback (sounds like a trumpet when you rev it) not sure if thats normal on moggy's tho?)

All gaps seem to be set fine, timing recently done & ok, oil & water consumption seem normal, compression test ok... all got me a bit stumped!


Anyway, any suggestions welcome... going to keep having a play around & see what I can find!

The only thing thats got me wondering is the carb piston had a bit of gunk on it (when I first got her) but was since cleaned. might strip back down to make sure its not there again.
Only developed this problem over the past couple of weeks, still hasn't been driven for more than 10miles :/

[JPX877J]

I shall echo a certain other user

It's never the coil XD

[MarkyB]

Carb piston seems like a good bet.

[beero]

A dirty piston in the carb can give this symptom. Take the plunger out of the top of the carb, lift the piston and make sure it drops with no resistance with a nice "clunk" and make sure there is oil in the piston before putting the plunger back. If the piston doesn't drop cleanly then dismantle it and clean with carb cleaner. You may need to centre the jet as well.

[the_count]

cheers everyone,
going to have a play around abit more tommorow, I'm definatly leaning toward either the carb or possibly a split vacum. will update when ive had another tinker!

[bmcecosse]

It's NEVER the coil - put the old one back on. Slightly sticky throttle cable will give this - also incorrect mixture and /or timing. What are the compressions? Is the vacuum advance working? And connected? Optimise the ignition timing and mixture for best idle - set it slightly fast at first.

[the_count]

It's NEVER the coil - put the old one back on

Update:
Playing around with the mixture has indeed helped no longer dipping below idle, or cutting out. Is still slightly dipping below when the clutch is down, but im going to have another tinker later... I think its running slightly rich as its started poping every now & then but I dont think its far off now

The vacuum is working, but the pipe is abit dubious and does seem to have a slight leak around the dizzy end, so will get another just to be sure.

[chesney]

It will always dip down with the clutch, it's the resistance from the graphite bearing rather than a 'conventional' bearing. Why you should avoid pressing the clutch for longer than necessary!

[the_count]

good to know, cheers!