Diaphram maybe

[Andrew S]

Quick question. Trying to sort a friend’s problem of when you pull away, it stutters or holds back although the engine revs freely and smoothly when idling. Put a strobe on and timing is spot on, tried revving it and although the timing advances, it’s not off the scale. It has new electronic ignition on but it has not cured it, new coil, new leads, plugs etc. We have had the carbs apart and level checked, new valves fitted etc.

Anyway, today we had a run out and I suspected it could be the vacuum diaphragm on the distributor, so pulled the vacuum pipe off, it is fine and really goes and we did 50miles with not one hiccup.

Does my diagnosis sound right, being that the diaphragm has failed?

Cheers
Andrew

[philv8]

wheres all the technos

[StagnJag]

Last time I had symptoms like that it was when there was no oil in the carb dampers. That's all that springs to mind, so you might not be far off thinking that its the diaphragms.

Rgds

Dave

[PaterB]

I'd check the dizzy too - ignition advance should go off the scale under heavy revving from idle. Check if vaccum advance works - if you suck on the pipe the electronic pickup should slide and return freely on the baseplate in the dizzy.

[GDPR]

That's a symptom of a rotor flashing through under load - swap it out with a good one...

Caps can fail in the same way too.

Ignition advance will only go off the scale at high rpm and high vacuum together. You can't imitate that with the car stationary.

Having just re read the original post, it could be the rotor location lug worn that means the spark can't make the gap on full advance, again rotor renewal is the answer. Worth checking the internal distributor wiring isn't going open or short circuit when the baseplate moves under vac advance - you'll need a mityvac or similar to operate the vacuum capsule. It would explain the symptoms going when the vac is off

[Andrew S]

Thanks a lot guys, wil check more then before ordering parts

Cheers
Andrew