Engine running problems

[sbu]

Dont know if anybody can help.I have a 912 with a fuel/running problem.The engine has been rebuilt, is standard with the exception of having Webers instead of solex carbs.The car starts ok when having been stood, however when i travel approx 3 to 5 miles, it starts to miss and backfire and run very rough, it then cuts out.It will not start.Looking at the engine i have a small fuel filter fitted on the fuel line just a short distance from the fuel pump, when it wont start the filter is almost empty of fuel and doesn't seem to fill with fuel.It can then be left for say 15mins and then eventually it will start but again running rough.
When this happened the first time i eventually made it home after a few stops.To date i have removed the fuel tank and emptied it of fuel as the car had been stood for some time with the same fuel.We then flushed the fuel pipe from the engine to the tank, some debris did come out, we flushed it with fuel at least 12 times to clean it all through, i fitted a new fuel filter and cleaned the fuel pump filter, we also checked the filter at the bottom of the tank, then put fresh fuel in.As a result it did start better, but still seemed to miss and backfire at high revs.It also still does the same thing after 3 to 5 miles, cuts out etc.It did again restart after 15 mins or so.
I am not sure if it may be the petrol tank vent pipe, on my car there seems to be a wideish pipe from the top of the tank, which then reduces down in size and then the breather pipe goes down behind the tank to the chassis.The pipework does seem to be a bit of a mish mash arrangement, and there seems to be a lot of pipe eventually working its way to the chassis.My next step is to possibly change this pipework to see if the tank is breathing ok and creating a vacuum for the fuel.The other possibility is the fuel pump.
The carbs seem to be running rich hence the backfire etc, but they had been set up when the engine was fitted.
I appreciate it may be a matter of elimination but has anybody any ideas, in addition any idea of the correct route of the breather pipe from the tank, and where i might get the correct pipework.
Any help would be greatly appreciated.

[Alan @ CanfordClassics]

Hi, where are you based. If near us (Dorset) you are welcome to bring it here. We are building 2 912 motors at the moment and would be happy to help. Or call me tomorrow in case we can help? Just a few ideas are, fuel pump, could also be electrical (coil failing), the tank also does need to breath correctly. What year car is it?

Hope you get it sorted

Alan

[sbu]

Alan,
Many thanks, located in North of England so some distance, car is a late 1965 built.

[Alan @ CanfordClassics]

Hi, I have a November 65 912 in the workshop and will grab so e pics of the vent system for you.

Alan

[sbu]

Thanks

[100702mark]

I'd be tempted to take a look at coil and leads as they often breakdown over time and problem only manifests itself when hot.

Regards

Mark

[nickT]

Hi, could be a restriction of fuel in the pipes from the tank to pump, I'd replace all flexible fuel hose and blow the hard lines through.
Nick.

[912uk]

that sounds like Fuel issues.

Check float levels, when running.

have you replaced the pipe from the tank to the start of the steel pipe?

Change all rubber pipes

Also have you cleaned the finger filter ( brass ) in the fuel tank? it normaly has a glaze on it over time and you lose so much surface area.

Also have you got some sort of non orginal fuel pump running in line? ( remove it )

Check the condition of the steel pipe that it is not damamged ( kinked ) in anyway that would restrict the fuel.


After all that is done and your happy with the right carbs for your 616 motor as this has happened before wrong carbs for the car.


then on to

Are the correct jets in the carbs?

are they damaged in anyway?

Set up of the carbs.


But does 100% sound like delivery of fuel issues on demand. Not tick over.

also check that the new carbs you have are infact suitable for the 616 motor.

[911-356 dave]

Hi, I am in the North of England if you want to come and see my breather pipe system you are welcome.
Thanks Dave

[Dingbat]

Hi
could be fuel supply but you have had a look there and done the obvious stuff, I may go with the other chap and suggest ignition stuff, such as a coil failing when hot, or condenser, that can result in a lot of crackling and popping or indeed the leads, Bill.

[100702mark]

The general rule of thumb I was always taught was if it happens above a certain rpm then look to fuel then ignition. I suppose this makes sense as the higher you rev the more fuel is needed.

However, if the problem happens after a certain period of time it tends to be heat related so look to the things that break down with heat which tend to be ignition related.

Perhaps just think back to original symptoms and think are you recalling them correctly, if you are then they sound heat related.

Not sure where you are up North but happy for you to come round to view breather set up if anywhere near to Colne, Lancs.

Regards

Mark

[DustyM]

Check the routing of your fuel pipes ( especially if they have been replaced with copper, which absorbs heat more readily than the original steel pipe ) sounds to me like the fuel is vapourising the pump then gets a vapour lock and can't suck up the fuel. Once the lines cool the fuel returns to liquid and everything works again.

Jon

[912uk]

I still think it's fuel starvation when the car is up to temp and speed.

you must at least check your float bowls when it's doing this I recon they are empty..

but what I do know

[johnM]

Alan,
Many thanks, located in North of England so some distance, car is a late 1965 built.

Any where near Kendal?

Go and see Mike Bainbridge, he will sort it out.

http://www.mbporsche-engineering.co.uk/

You wont be dissapointed.

Kind Regards

[womble912]

Hi,

Did you resolve this as, I am having the identical problem!?

Womble.