Twin Stromberg CD150 synchronisation

[daver clasper]

Hi. I have read that air/throttle butterfly valve balance is not so pertinent at higher RPM, which seems logical and therefore I assume is more of an issue a idle/low RPM, which also would make sense.

Also I have read that if the balance is not correct the carbs are fighting each other, what would be the symptoms of this please?

Car is running well, though showing big difference in plug colour on individual cylinders  from the same carb recently (more so after idling/slow moving in traffic for a while, no1 white, no 2 very sooty). Thought I would ask if any imbalance could affect mixture?, though not sure how?, to maybe look at after investigating other, maybe more likely possible reasons, have some ideas, though any advice great. 

Thanks, Dave 

Edited September 1, 2023 by daver clasper

[glang]

My take on it Dave is that with severe carb inbalance (think youre right that it has less effect at higher throttle openings) 3 cylinders are doing less work that the other 3 even though all have correctly set mixtures. I cant see this would cause much plug colour difference between the two banks of cylinders which is more likely to be down to the carb mixture adjustments being different.

If however you have random plugs with different colours this could be air leaks, valve adjustment/damage or misfiring 

[daver clasper]

Thanks Glang. I have changed plugs and HT leads around in case of weak sparking, no difference.

Fitted new manifold gasket a few years ago (one piece, for Mk1 Vittese, though some folk advise using two as thinner than orginal?) and nipped up the nuts recently, though not sprayed brake cleaner around yet to check for inlet leaks. Thought I would also do do a compression test, as assume if lower compression on a cylinder then would run rich?, and will check also valve clearance.

After that, then out of ideas. Probably wont worry too much as only a few K mileage a year, though aware, not ideal to be running massively rich for possible bore wash/carbon build up, or weak for valve/piston damage. Who knows?

Cheers

[glang]

which cylinder(s) is it? I have read that the manifold doesnt deliver equal flows to each cylinder especially if the casting is poor around the internal dividing points. To solve this some owners modify them but of course this is quite a specialised job which really needs a flow rig.

As you say, low compression would give poor combustion...