Stag not Idling

[SwissSteve]

Stag carb replaced with Weber Carb. Ran perfectly for a week.

Then one day the car started but will no longer idle. It runs smoothly around 3K +RPM with
choke or foot on the gas pedal but will not idle, just stalls.

Have tried the weber carb on a second stag and it works perfectly so
the carb is not the issue. Have replaced the coil, distributer and fuel pump
without any success.

Any ideas what to check next?

[GDPR]

I’d get back to the carb supplier for his advice....

Who supplied the distributor?

[SwissSteve]

Yes, I suspectef carb issue so I contacted Webcon, who supplied that originally and suspected blockage, dirt in idle circuit. This was also their impression so I stripped the carb and cleaned it out with compressed air and it made no difference - I have a friend with the same carb on and we swapped it out and the carb ran perfectly - so rules out the carb....thx though for your input

[Kithmo]

I would guess, that there's an air leak somewhere on inlet manifold or vacuum connections to it or to crankcase breather system.

[GDPR]

So you need to dig deeper - ignition timing good? What have you done breather wise and if you have a PCV what about an air leak into the vacuum side of the PCV? Have you sprayed WD40 around the inlet manifold to see if you have any air leaks there, and clamped the brake servo vacuum pipe?

I am making the assumption that all 8 cylinders are firing of course... but the usual loss of low speed running is air leak, or on the Weber a blockage in the idle circuit - this can be roughly checked by placing your hand over the carb intake with the engine running, gradually, and see if the engine picks up..

[SwissSteve]

Thx Kryten - I shall put the carb back in tomorrow and arm myself with WD40 and check the timing. The PCV is currently unplugged being not connected to air intake and will recheck brake boaster pipe. Where would i check on the vacuum side of PCV? Thx

[SwissSteve]

Thx Kithmo for response and odd thing here is that this started from one day to the next in underground parking..

[SwissSteve]

Just so I don't give a wrong set up - I have a hose from the rocker cover connected to nothing at the moment and the car ran fine before in that state

[GDPR]

You say the PCV is unplugged from the air intake? Could you clarify? A pcv usually has a connection to the inlet manifold that runs at engine vacuum - this alters the routing of the crankcase breathing according to load/vacuum - I’m assuming the vacuum port to the manifold for the pcv is not connected and/or plugged?

[SwissSteve]

There is one hose from the intake manifold to the brake boaster and another hose from the rocker cover, which is the one currently disconnected. This was the routed into the Stromberg manifold replaced with the Weber carb.

[GDPR]

OK then - start by back to basics. Before checking ignition timing, just check the distributor baseplate with the module hasn’t slipped or busted the pin to the vacuum advance and the baseplate is flopping about, if ok, and the ignition timing is badly retarded, where it wasn’t before, then you have a failure in one of two usual places - the roll pin that attaches the distributor gear to the shaft can shear, but also, and come across this too many times, the dowel on the jackshaft shears and the gear moves slightly on the jackshaft retarding the timing - this is usually due to a momentary jamming of water pump/oil pump or distributor, usually on cold start. Because the jackshaft sprocket bolt is tabbed and keyed to the sprocket, the chain movement tends to tighten the bolt and continue to drive the shaft, albeit retarded.

If nothing else was different from the previous time it ran right, and the timing is well off now, reset it to check it runs ok, but then work backwards to see what went wrong..

[SwissSteve]

I will check this tomorrow and report back. Many thx for the advice/help here

[GDPR]

Do that - I may not be able to reply from being switched off, but I’ll still be able to read as a guest

[Kithmo]

As this happened overnight, I would check all the vacuum related hoses/pipes for splits. Another thing to check is the fuel filter for water ingress in the fuel.

[SwissSteve]

Ok great and thx again