Intermittent & long-running fuel flow problem - G68 area

'H' '91 Clipper Cabrio 1.8 carb (Weber) 150K

First I want to rule out the obvious by saying what's been replaced/checked:

New tank / s/steel filler neck & new tank checked and cleaned again / replaced fuel lines / new pump / new filter

My garage (automotive engineers, who specialise in VW/Audi and rebuilding old cars … porsche etc ) are stumped as this has been on-going now for years (had the car for last 12 years). Tried adding in a swirl pot despite being told this was not req'd with a Weber in place, but couldn't get that to work.

I have suffered the intermittent apparent fuel starvation that causes loss of power, 'jumping', back-firing, and usually means stopping for a few minutes before setting off again. Usually does not occur until been driving for some time  but also seems to happen when going uphill, but this is not always predictable and can go for days without any problem or can happen more regularly.

Originally the car had no swirl pot fitted and the (botch) three-way plastic 'Y' tube that joined the fuel lines to/from pump, to tank, and to carb snapped and the garage then set up the following system:

1. fuel line from the tank has a filter and goes to the pump,
2. fuel line from pump goes to the carb and
3. fuel line return to tank is blocked off and redundant.

AS I WANT TO SELL … I need to get it sorted once and for all and can't help feeling it must be something really simple but so far escapes everyone who automatically suggest what I have already done/replaced (above).

WOULD REALLY APPRECIATE ANYONE NEAR GLASGOW/EDINBURGH WITH KNOWLEDGE WHO COULD HAVE A LOOK AND SEE IF THEY CAN SPOT WHAT MISSING. EVEN SEEING WHAT ANYONE ELSE HAS IN PLACE FOR THE SAME MODEL WOULD HELP !! I'M WILLING TO TRAVEL ALMOST ANYWHERE TO GET THIS DONE !!!   

Cheers,

Bill

Thanks

the swirl pot goes between the pump and the carb, 1 line from the pump, 1 line to the carb and last line is return to tank. you shouldn't need to remove this even if a webber is fitted, its there to smooth out fuel flow to the cabr and filter out any air bubbles.

is it definitely a fuel issue and not an ignition problem or carb icing, is it worse when the weather is wet? another thign it may be worth totally stripping the carb down to give it a damn good clean out inside, replace the gaskets and reset the float height etc. there are some extremely small holes in the jets which are easily blocked

Thanks for the feedback.

Pretty sure its a fuel issue, and not worse in wet/cold weather. Away from home at present so once I'm back will look to re-try connecting and running with swirl pot in the flow system. Failing that will look to get carb examined.

Cheers.

Bill

ive seen a fair few plumbed in without the swirl pot and running fine though, my thoughts are maybe you have a pinhole in a fuel line which is allowing air into the system? without a swirlpot to filter it out this is upsetting the carby.  cant really think of anything else as you have checked all the stuff i would normally suggest you look at!

Finally got the swirl pot linked up the right way round and gave it a go.

All seemed fine as it idled, with the long-since blocked-off return fuel line happily returning fuel to the tank whilst the fuel inlet line showed fuel coming into the fuel filter and heading for the pump. I tried a short drive but managed only 50 yds or so and it just died with no power - an apparent lack of fuel. After a short pause it eventually started after a few turns of the ignition appeared to bring in more fuel. This continued for another 3 attempts, again stopping after about the same 50 yds.

The concept of the swirl pot certainly seemed to be a logical solution to the original problem, but I am totally lost on what must happening now - any ideas ?

In respect of plan 'B' and working without a swirl pot was my garage right in blocking off the return line or, if not, how would the three-way fuel line mix come together in the absence of the pot which has three line connections ?

Bill

ive only ever seen it done with the return capped off, the cars ive seen liek that never had any running problems.

when it cuts out, can you pop the feed line off the pump and crank it over to see if fuel is coming out strong? if not then i wonder if the pump is weak.  is the drive pin part of the pump, or does that stay in the block? i'm wondering if the pin has worn, or maybe the drive lobe on the intermediate shaft…

oh and pop the filter off and look in the inlet side, see if there is any dirt or rust in it. the filter can look spotless from the outside but be full o cack when you look.

oh, and has the in-tank sender unit been checked? soem have a filter on the end which can get clogged. id also want to blow thru botht the feed and return pipes to ensure its flowing free. oh and the pickup pipe should be sat at the bottom of the tank, i maybe it has fallen off?

I think I can basically dismiss all of these.

New fuel lines in place and pump (Piersburg) is brand new. After I replaced the fuel lines at the engine end the Garage checked the tank end lines, pick up, etc and all in order.

Seems the car/carb doesn't like the swirl pot and will have to return flow back to previous system with return blocked off, cos at least the car would run like that, albeit with the original occasional & intermittent lss of power.

Got another garage recommended to me when at last weekend's classic show at Knockhill. It's up in the north of Scotland but the VW mechanic there has worked on Mk1's since they were new and probably one of very few still working on them, so worth a try and the journey up there.

Thanks as ever for all the help and suggestions.

Bill

the swirl pot may be showing up a pressure issue though, when you block off the return no fuel can go back to the tank whereas it can with it fitted. it shouldnt matter either way. webers own fitting guide tells you to keep the vapour seperator in place so it SHOULD work.

liek i say, i wonder if the pin on the pump or the lobe on the intermediate shaft is to blame, or maybe somethign random like the gasket between the pump and block is too thick?

THE PUMP GASKET STRIKES A CHORD !

IT IS PARTICULARLY THICK AND I BELIEVE A BIT WORN, BUT DOES NOT COME AS A REPLACEMENT WITH THE NEW PUMP. ARE THEY AVAILABLE TO ACQUIRE SEPARATELY ?

to ensure its deffo correct i would go to vw:
035 127 301 C - flange - 5.5+VAT

that comes with the flange->block seal, if you want the pump -> flange seal its:
049 127 311 A - o'ring - 1.68+VAT

its a bit of a long shot really! but as i say while its off have a good look at the lobe on the int shaft, and the pump pin too. ive never heard of them wearing but you never know!