Tickover

[pbottomley]

Well I kow have marvin running, but what is very strange is The engine will not run unless I have the choke out, and worse still is that the tickover (if you can call it that) is around 2000-3000 rpm and its slows down to 1000 or so rpm backfires then speeds up to 2000-3000 rpm slows backfires etc... seems almost to have a life of its own!!

Ideas welcome or bacon Sandwichs on offer for the right fix

[bulldog]

airleak?

[Stu]

Dirty Carb (throttle plate/air piston)?

[Kat]

airleak's a possibility... choke full on makes mixture richer, only way to get a mixture that'll burn if there's air getting in somewhere where it shouldn't.

A sneaky one that caught me out once...

...airleak from knackered brake servo. Disconnect the pipe from inlet manifold to servo and block the manifold 'ole up to check that one.

[lambaj]

Paul

Zenith dowdraft or Stromberg ?

Blocked Main jet on Zenith, choke gives fuel and raises revs.?
Still sounds like an airleak. As Kat said, check servo vacuum hose and anti return valve. Also check Crank case/rocketcover breather valve is not stuck open.

TTFn
Tony(HA21)

[pbottomley]

Tony:

Its a Stromberg 150CD, the car (HA) has a servo fitted, and at the minute I am running the car with no breather fitted nor air cleaner (so i can see whats going on)

I think I will just disconnect the servo, and refit the whole manifold etc (as i have a non servo manifold, which wioll test the air leak theroies) I will also change the rubber diapram in the carb and let you all know the outcome.

[lambaj]

Also check the vacuum signal hose from near the insulating carb plate to the vac advance unit on the Dissy. Also make sure the throttle linkage is not badly adjusted so as the engine rocks about, it opens and closes the throttle..... Broken return springs on the carb throttle spindle are not uncommon. I expect it is not the diaphram, blown diaphrams result in nothing more than a tickover as the dashpot does not lift.
Also check carb insulator has not been cracked by over tightening, and that both gaskets are fitted.

I've never heard of a non-servo manifold. All "90" powered cars had disc brakes from factory, so all had servos as well. You can always just block off the vacuum port.

Good luck
Tony (HA21)