Misfire at idle

[nice2day]

Well done and mystery solved. What made the diagnosis difficult was that the effect only took place after the engine had been idling for a long time. With an air leak you would imagine the symptoms would be the same after the engine had idled for any amount of time but here is an extreme possibility: As the manifold studs were heated they expanded and became longer thus increasing any air gap....more likely is that the engine and carb warms up and the extra weak mixture just tips over the limit for the engine to run cleanly...

Les

[Blurredman]

It is an interesting theory.

It definately took a bit more persuasion and periodic 'flicking of the fuel enrichment lever' whilst getting my helmet on when this lean condition was apparent.

What I thought interesting was I presumed air leak = higher idle (which was true when you couldn't dial it in properly)- but also a low laboured idling too..

I used the brake/carb cleaner/wd40 technique in all areas of mating, but nothing changed the engine- so presumed there was no leak- and yet, obviously there was...

[Puffs]

If we're back to the carb heating up due to little flow @ idle, and a thermal connection with the barrel (the very first thing suggested): that doesn't really make sense, as the plastic flange is in place. So the construction is the same as in all other ETZ's, and they don't all have that idling behaviour.

The 'studs heating up & expanding' model could explain it, but why would those studs all of a sudden start to heat up when the idling begins? More likely is the opposite: the studs keeping the same temperature (as the barrel), hence same length, but the manifold warming up due to less flow, hence expands, so that the gap (if there is any) actually gets smaller.

Maybe a combination of a small gap + carb heating up? Grasping at straws...

Another enigma.