Popping back through the carb

matt h · 30 August 2007, 08:29

1935 Rolls V12 50hp popping back through carb and exhaust,Literally nil performance after 1000 rpm,(does idle very nicely and starts fine),
compressions all good, rebuilt carb,(made no difference)
new plugs, small crack in one of the dizzy caps but not tracking through or near it, new condenser and points fitted,
have run WD40 around manifold joins with engine running, all looks good and no increase in RPM,
it uses twin coils and dizzy caps, you can switch one off and use the other side, but its still the same,(pops and bangs) which now i guess is pointing to the carb and inlet side of the engine,
and there is huge cost to taking the next step of taking manifolds and heads of i thought id test someone's brains before charging ahead,
Help!!!

Nasher · 30 August 2007, 08:55

Is there any sort of advance/retard mechanism that could be sticking etc?
As it sounds like it could be timing to me, although there are of course other possibilities.

The carb could only be working on the idle jets if a separate circuit is fitted.

Nasher

Nos4r2 · 30 August 2007, 12:21

How is the charge to run it generated? Could be low voltage to the ignition system.
I assume it's a mechanical fuel pump? If it is could worn needles be overfuelling it when you rev it and the pump speeds up?

Out of interest, what's it in?

matt h · 30 August 2007, 14:33

new needle inside set for float 5/8 inch for top of carb, so perfect fuel height, new Heavy duty battery,

matt h · 30 August 2007, 14:35

there is new needle inside set for float 5/8 inch from top of carb, so perfect fuel height, new Heavy duty battery, it uses twin su pumps to a single outlet, (bit like an older jaguar)
the advance and retard are fully adjustable through the steering wheel quadrant through to 10 degrees either way, have also advanced it manually through 20 degrees, still pops and bangs,
im going to put on 2 new coils tonight ,elimination process i guess, will put a picture on later, keep ideas coming,

jwalker · 30 August 2007, 17:08

Weak mixture, ignition timing or sticking valves is my guess. If you can retard it manually to around TDC then you can eliminate the problem as ignition timing if the poping still occurs.

matt h · 30 August 2007, 20:30

Sorted!!!!

two new coils did the trick, i guess i was looking too in depth and not at the basics, thanks you all for your input,

fast fred · 01 September 2007, 11:18

Quote:

1935 Rolls V12 50hp

?, what's that look like , gots a pic of it.

codprawn · 01 September 2007, 19:14

Quote:

Originally Posted by fast fred

?, what's that look like , gots a pic of it.

Yes come on - I really want to see this - thought this thread was about some scabby old outboard so didn't look till now.....

Is it a Phantom III like Goldfinger's??? If so I will challenge you to a duel with bowler hats!!!