Vacuum advance misfire

[Vic Butler]

Please everyone disregard my comment about the centrifugal advance moving the base plate. Of course it doesn't. I'm a complete idiot. I must have had a brain fade.
The rotor arm shaft is actually in 2 pieces. If you hold the drive gear you can twist the rotor arm separately and that is how the ignition is advanced. The base plate is activated by the vacuum advance so I will now return to my original diagnosis that there's a break in the wiring or the earth wire if fitted.
Apologies for the stupid error. I'll put it down to age (any excuse).

[Ian F]

Thanks again Vic, I clearly need to have a closer look at a distributor at some point! Apologies for the misleading question......

Ian F

[Mudguardandy]

Charles,
I’ll check the plug gaps just to be sure.. 035
From memory. But as I’ve said she’s fine with the vacuum off, and with or without vacuum,
no misfire at tick-over.

[Ian F]

It would be interesting to know whether the misfire at higher revs is only when the engine is under load, or whether it misfires under all conditions at higher revs? (ie when stationary and revved).
I think it is commonly encountered that when under load any weakness in the ignition is likely to show up as a lack of spark in one or more cylinders.
A new set of plugs correctly gapped would be a good starting point, but there would still be the vacuum advance puzzle to sort out.

Ian F

[Vic Butler]

On tickover the vacuum advance on a chrome bumper B isn't operative. Gradually increase the revs and see what happens.

[Mudguardandy]

I’ve replaced plugs with new v recently with ( NGKs ) ready for summer so very few miles on them.
The misfire happens without load in the workshop. Nothing at idle, but gradually kicks in
More as revs are increased. Holding the revs
At 3000 the misfires seem to increase.

[Ian F]

Well I guess that should make it easier to sort out! A fault which only manifests itself on the road at high speed would be much more difficult.

Ian F

[Vic Butler]

That proves that the movement of the base plate causes the fault. It must be a fault in one of the wires, probably under the insulation or in the grommet in the distributor body.

[Ian F]

Well that sounds very straightforward!!

Ian F

[Mudguardandy]

I agree, everything saying baseplate movement
Is the problem. But vacuum removed, the baseplate still moves with the weights. So why wouldn’t it misfire then ?