Hi guys ....... Just acquired a 1986 1 litre MK2 Breadvan with only 41,000 miles but am having carb problems. The engine seems to be running rich as the plugs are very black but the main problem is that after 15-20 miles the engine just cuts out completely. If I sit for a few minutes it will start again no problem and off I go again for another 5-10 miles and then it dies again. Obviously a professional carb set up should cure the rich running but what should I be looking out for in relation to the cutting out. Any suggestions very welcome from the Polo experts.

could the choke be sticking on

Could be carb flooding because of crud in the shut-off valve or worn valve tip

or valve seat

(sometimes called a needle valve although unlike SU carbs say it doesn't taper

on Solex or Pierburgs or Webers).

Fuel keeps running into the well even though the float has risen.

That would give very rich running then cut-out once mixture too rich.

Do you to have to crank it a lot to start it again?

Or rusty-sludge in the fuel pipes. The flow gets impeded and you can drive only

one carb's well amount of fuel at a time. Rest and the sludge drops back down

to the lowest position and you can start again... cranking refills the well at

low pressure. Drive a bit and the suction of the pump pulls the sludge to where

it blocks again.

How clean is the fuel filter?

I replaced the fuel filter and cut the old one open to have a look inside. TBH it wasn't too bad. The over fuelling sounds likely so I'll have the carb off and have a look. Many thanks for your input.

This happened to a mate of mine, he took it to a vw place here in cov and straight away they said it was the distributter cap. He sorted it and he ent had one prob since.

i'd check the dizzy but I'm no pro

Thanks for the input guys. I had replaced the dizzie cap, plug leads, plugs, air and fuel filters prior to the test run where the problem arose. This was after a three month re-build after buying the car. Strangely enough when I checked the oil level at that time I found it to be way above the maximum mark. I actually had to drain just over 2 litres out of the sump to bring it down to the max level mark. At the time I just thought someone had seriously over filled it and thought 'what a dick'. More about that later.

I wasn't too impressed with the amount of fuel flowing through the clear fuel filter so I swopped the fuel pump for one off off another car and that seems to have solved the problem (fingers crossed) Have now bought a new fuel pump from GSF (obsolete from VW) for £14 plus vat. so it's a cheap fix as long as it keeps going.

I have since spoken to a few mates and apparently the fuel pumps are prone to leak internally when they get old. The petrol which escapes then runs into the area under the cam cover and then down into the sump. (the fuel pump is bolted onto the back of the cylinder head as you all know). This would explain the extra 2 litres of fluid in the sump and come to think of it the oil which I drained out did seem pretty thin. The up side is that the engine internals should be squeaky clean. Obviously I have now changed the oil and filter too.

Comments welcome. Am I reading too much into it or has any-one had a similar experience.

Edited 7 July, 201016 yr by leon263

This sounds like a similar problem to what i used to get with the weber on my 1.0l. I eventually put it down to crap somewhere in the fuel system, since when i took the jets out of the carb, and blew through them, it would cure the problem for a while.

Throw some carb cleaner/wd40 down the carb first, and blow through all the jets once removed from the carbs. Simplest things first

Thanks for the input guys.

...snip...

I have since spoken to a few mates and apparently the fuel pumps are prone to leak internally when they get old. The petrol which escapes then runs into the area under the cam cover and then down into the sump. (the fuel pump is bolted onto the back of the cylinder head as you all know). This would explain the extra 2 litres of fluid in the sump and come to think of it the oil which I drained out did seem pretty thin.

Fascinating.

Basically carbs stop working because the mixture is too rich or too lean.

You describe rich symptoms (sooty plugs), but the fuel pump failing causes a lean problem ...

too little fuel.

Unless, perhaps, some small fragment of the perished pump rubber diaphragm travelled along the pipe to the carb, got past the carb's own inlet filter

and blocked the needle valve open. It's a long shot. Oh, wait it's a Pierburg not a Weber, in which case there is no filter after the pump, only before it.

Unless it's not soot on the plugs but burnt oil forced up past the piston rings... "squeaky clean". maybe. With that much oil an fuel I'd expect your oil breather pipe to perish real soon now too. I think it enters inside the air filter. There may be trouble ahead.

I've not had a fuel pump leak but I reckon it's definitely better for fuel to leak into the head than onto the inlet manifold, hot block, drip onto hot exhaust or spray out in a fine combustible mist.

One more reason to check oil level every week.

My Pierburg fuel pump has a small breather hole which I would expect fuel to leak out of. Depends on internal construction I suppose.

I imagine the pump piston mechanism is at oil pressure so there needs to be somewhere for air to go when the actuator for the pump diaphragm moves back and forth in its chamber.

I've done around 60 miles without mishap since the new pump although I still seem to have a slower flow through the fuel filter than on my other car so I reckon there may be a restriction (sludge, rust etc) at the tank outlet. In fairness, the other car had a new fuel tank. Something else to check. When I referred to oily plugs and smokey exhaust etc, this was before draining the excess oil which I reckon was being pumped up the crankcase breather into the air intake and straight into the carb if the state of the air filter I took out was anything to go by. Plugs are now as you would expect and the smoke has gone. After the cutting out episode the car would start instantly after a short rest so that is what pointed me towards the fuel starvation idea as opposed to flooding.

Many thanks for your interest and input, I bow to your superior knowledge and I'll keep you posted.