Engine missfire at idle

[petebugsy]

I hope i have posted this in right section, and i hope someone here can help.

Just finished rebuild on 1641 engine.
New barrels and forged pistons
New VW mexico complete cylinder heads
Secondhand 34ict carbs
009 dizzy

Engine altogether and running strongly, however at idle cylinders 1&3 don't seem to be running (can pull plug leads with no noticable change)
I have changed everything i can including the carbs to another set of used i have, all of the ignition system including plugs, leads, dizzy and coil.
Carried out compression test all 4 around 145psi
carried out leak down test all show 90% sealling and what leakage there is seem to be past the rings (no suprise there)
Checked valve clearances.

Anyone got an idea please!
i've spent the last 2 days going round and round so any help gratefully recieved.

Cheers
Pete

[Lids]

have you checked you have spark on #1 and #3?

have you checked for air leak round base of carb manifold?

do you have fuel?

check valve clearances.

[petebugsy]

Yes have checked for spark

Have tried spraying brake cleaner around manifold bases and also put some sealant on gaskets to be 100% sure

Fuel seems okay engine revs smoothly and cleanly, also i figured if carb problem then fault would be on both cylinders of faultycarb supply not one cylinder on each carb.

Have checked and rechecked valve clearances, also cranked with covers off to check everything moving as it should.

[Fastbrit]

On opposing cylinders? Hmmm, the common item here is the cam. Can you accurately check valve lift? Could be cam has got wiped out on break-in. You did break the cam in, didn't you?

[petebugsy]

Cam is standard orginal item that was in engine before rebuild so did n't need to break it in

Lobes where lubed on assembly and followers and pushrods all refitted in orginal positions so should be ok

visually checked that valves are all opening and closing (not sticking) and compression test shows valves are fully closing

[ian c]

its a standard feature .
it opens up the other 2 cylinders when you put your foot down . 


(check your float hieghts , linkages , leaks , and fit a balancing tube . that should fix it )

[benssp]

Hi pete, didn't see you at dubfreeze this year, must've come to your senses and stayed in bed

answered this question many times at work, try fitting a balance pipe between the two manifolds, this will help;D

[Dougy Dee]

Dual carbs. Funky miss at idle... They all do that. Put a balance tube between the manifolds and the 'problem' goes away.