Engine Running Issues - ADVICE NEEDED

[carlos77]

Hi all, thanks for the thoughts.

So fuel tank issue was looked at but wasn't deemed to be the culprit as we ran a separate external fuel supply to the pump, and had the same issues.

Carbs are clean and idle screw behaves as expected. We also swapped another set of Webers on and again, the same result.

Running electronic ignition, this was the first thing I suspected, annoyingly bought a new one (at least I have a spare now anyway) but want't the issue. We swapped the dizzy out for another 050 which ran points and vacuum condenser, but alas didn't solve things!

Valves are all free and clearances checked.

No closer to a solution I'm afraid.

[SeanP]

Are you running the insulators between the carbs and manifolds?
Do you have adaptors from the solex manifolds to the Webber carbs?
Have you replaced all of the gaskets in the inlet system?
Have you checked for air leaks in the inlet when the problem occurs? Heat has a way of opening up cracks in the manifolds.
When started does it idle without showing the symptoms or do the revs drop and the engine start stumbling?

[SeanP]

Are you running the insulators between the carbs and manifolds?
Do you have adaptors from the solex manifolds to the Webber carbs?
Have you replaced all of the gaskets in the inlet system?
Have you checked for air leaks in the inlet when the problem occurs? Heat has a way of opening up cracks in the manifolds.
When started does it idle without showing the symptoms or do the revs drop and the engine start stumbling?

[neilbardsley]

Any progress?

[hickepa2]

Carl, new to this thread... I am pretty ignorant of 912’s; I had a similar issue in my 911SC which was traced to pulse wire between dizzy and CDI breaking down (rather than failed) causing intermittent stops that were difficult to trace.
This may not even exist in your car but just in case.....


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[hashman]

Hi Carl,
I had some symptoms like this on a 356, it would run fine then after a while it would die.
The car had a mechanical pump and a 6 volt electric pump and for a while i could not resolve the problem.
Then one day when I had broken down I called the AA and the AA man who liked his beetles said I know what this is....
He explained that the pivot pin in the mechanical fuel pump had worn so that once the engine was warm the pushrod from the distributor was unable to push the diaphram up and down enough to give a good fuel supply.
So the next day I swapped my mechanical fuel pump over with a spare I luckily had and hey presto drove to silvestone and back fault free.
Maybe?
Karl.

[mycar]

^ Sounds good, the type of failure you only recognise with a fair bit of experience.

My only fresh offering is from an article printed in last months Registry mag. Just goes to show the smallest component failure can have disruptive consequences.

A worn out wiggly green wire.



Other than that.... take the car to Fenn Lane.

[neilbardsley]

Hi Carl,
I had some symptoms like this on a 356, it would run fine then after a while it would die.
The car had a mechanical pump and a 6 volt electric pump and for a while i could not resolve the problem.
Then one day when I had broken down I called the AA and the AA man who liked his beetles said I know what this is....
He explained that the pivot pin in the mechanical fuel pump had worn so that once the engine was warm the pushrod from the distributor was unable to push the diaphram up and down enough to give a good fuel supply.
So the next day I swapped my mechanical fuel pump over with a spare I luckily had and hey presto drove to silvestone and back fault free.
Maybe?
Karl.

I think Carl is running a electric pump which by passes the mechanical pump.

[carlos77]

Hi again,

all good tips, car is in storage at the moment so I can't access to easily, but definitely worthy of checking the connectors on the wires.

I have a mechanical pump and we tried an electronic one and bypassed the mech on, didn't change anything so suggests it's not the pump.

Everytime I see some glimmer of hope in everyone's worthy advise, bu alas most things have been tried.

I'm sure (hopeful) it'll turn out to be something really small and simple, but it sure is frustrating!

[Rupsol]

have you checked your negative earth? that may sound stupid but I had a beetle years ago with a rusty earth and ran like a dog - sorted that and we got to the winter and then it suffered terribly from carb freezing as I had replaced the solex with twin webers and individual filters - no pre-heater into carb! It was sold shortly after

[Winston Teague]

At this point in your despair i would trailer it to a rolling road. Run it from cold until symptoms appear, the O2 sensor will display the fuelling and the oscilloscope will show heart rate (ignition trace). Your man will spot the changes long before you 'feel' them. W

[Jesse]

+ 1 on mycars advice from the registry mag!

[neilbardsley]

On that front have a look on Peter Burgress' site. He is offering a tuning session for £80!

[neilbardsley]

PS I recently bought a fuel/air meter. I would over with it to investigate if you want.