Engine difficult to start following basic service

[mbell]

I agree that 55f8 is likely on the rich side. One easy check to get an idea is how many turns you have on the idle screws. If you only have less than two turns that MIGHT signal the jet is too big.

On progression holes, I'd be checking the position of the throttle plate relative to the first progression hole for your idle setting (remove progression cover and shine a light down the barrel throat). They should be positioned so that the progression hole is exposed to engine side just as you come off idle but not at idle.

If that isn't the case you need to investigate why, too much air going through the bypass so more closed throttle?

Or maybe webber miss placed the progression holes on some carbs. I don't have this issue on my 151s.

[alanr]

Thanks for that Eric,
Yes I will let you know if I decide to 'have go'.
Currently I run with the floats at 29mm and Spark Plugs BPR 5ES's to stop fouling, however 45F8 idle jets are hopeless for me in my Weber 31's. I have been running for a while now with 50F14 idle jets which seem ok'ish but are not perfect and as always I am on that constant quest for improvement..

Thanks,

Alan.

[h20hamelan]

https://www.webstore.com/item/Progressi ... /116562782

Keith has them for sale, I would guess you UK friends could share one as postage from the good old US of A will be $50 / £50

[Donels]

Just before you do any tweaking I would go back to the air filter. You scrunched it down to get it to fit so you've probably partially blocked its flow capacity, so the air to fuel ratio will be rich. No amount of tweaking will sort that out so have a look first.

[StressCraxx]

Reading through from the original posts, lots of good thoughtful responses. Two things come to mind.

My own experience with webers on the two Twincams I own - One stock, one full race.

Cold start with fuel present in carbs:
3 or 4 quick pumps, crack the throttle barely off idle, crank the starter and it fires almost immediately. Let it smooth out and then go.

Hot start:
No pumps. Crack the throttle barely off idle, crank the starter and it fires almost immediately.

One issue that will make for difficult starts is worn ignition points that are almost closed. Check the points to make sure the gap is within spec.
Second issue is a dying condenser. Starts fine when cold, gets hot and doesn't want to "condense" any more.
YMMV

[h20hamelan]

Good point on the condenser

If you have resistor ignition system, this will be less of an issue.

Full 12+V kills condensers, so if one accidentally leaves ignition on…