Problem identified - Stalling under heavy breaking... Why?

[Eurobox]

Yep as the title says, I have no fuel return pipe... 1990 1.8 GTII with Weber.


So heres the story so far, bought the car a couple of month back but it had a lumpy idle when I bought it but I did pick it up cheapish and had some idea of what the problem was, I've had a few rocco's over the years so took a chance on it, it drove alright and sometimes would cut out occasionally and after driving for a while if I took my foot off the gas it would hunt and sometimes cut out alltogether.

This made me think rust in the tank and blocking the pickup pipe, you know the usual. Sooo I opened the inspaction plate and lifted out the pickup and sender and had no blockages but there was particles of rust knocking about in the bottom of the tank (the previous owner had changed the filler neck). So I chucked in a couple of ample magnets close to where the pickup pipe is and enlarged the holes on the pickup, then removed the fuel line from the filter which by the way looked pretty clean and applied a hand pump to blow it through, and again in the pipe from the filter to the pump so it's definately all clear, I used a jug to catch whatever came out to check for particles of rust but there was nothing and was completely clear.

Then I removed the Weber and stripped that down and gave it a good clean out with carb cleaner but that looked clean as a whistle inside so I've discounted that from my investigation, oh and by the way I did check the rubber gasket at the base of the carb and that looks fine, infact before I removed it I had a spray about it with a tin of wd40 and had a bit of a wiggle but this revealed nothing so I'm pretty confident there were no leaks.

Now.. this was starting to confuse me because I was convinced these symptoms pointed towards fuel starvation and was sure I'd find a carb full of crap. When I tried to turn the car over to pull the fuel through nothing happened so I turned it 20 times and still no fuel in the filter so This made me think that the root cause of the running problem was the fuel pump, and this seemed to work with my fuel starvation theory. So I ordered a new pump and fitted it today and it started on the second turn and ran.

Then I set the fuel mixture fully in then 2 turns back then in a quarter and set idle to 850 and seemed to idle fine, so I took it out for a drive and I have exactly the same problem that I started with, drives well going easy but if I give it some, not only does it feel down on power but when I lift my boot off and dip clutch it starts to hunt around 250-400rpm and dies seconds later. Starts up again and idles fine but then when I drive it even easy it starts to hunt soon as I take the boot off.

Then I noticed that the fuel filter isn't full, it's just a trickle of fuel running through it, I remember it was like this before I changed the fuel pump too, now I've cleared the whole system and fitted a new fuel pump, so surely the filter should be full?

Then after digging about on here a bit more I keep finding posts mentioning fuel return and Y pieces and T pieces etc, so I went looking in my car and I have none of that, the fuel return pipe where it is secured to the bulkhead adjacent to the fuel feed pipe has been bunged with a bolt. Could this be my problem and would this explain why my fuel filter isn't full and cause my fuel starvation?

Also I don't understand why this would have been done at all?

I need help here folks...

[go-for-it1]

Has the fuel swirl pot fitted between the fuel pump and the carb been removed? The fuel return is a restricted flow of fuel back to the tank from the pot which just keeps the pot full, and when the carb is not taking much fuel e.g. at ldle the excess goes back to the tank. I wouldn't have thought the lack of a return would cause fuel starvation, in fact the opposite as there would be excess fuel. Pull the fuel pipe off the carb and turn the engine over whilst allowing the flow of fuel to flow into a jam jar or something, if there is a good flow then that is not the problem. Check the vacuum advance is working correctly by sucking on the pipe which goes to the vac unit on the side of the distributor, and with the dizzy cap off you should see the plate rotate if correct. Also check the other end of the pipe is connected to the pipe coming from the manifold. Problems with internally collapsed fuel rubber hoses have been highlighted previously so poor fuel flow could be related to this so change the hoses if in doubt. Loss of power could also be the coil breaking down under load, replacement is the only fix. Also fit a new inline fuel filter as I have had brand new ones which would not pass fuel through properly! Hope this helps a bit.
Rob

[Risocco]

Yo, back when I was running a single weber carb I had all these symptoms, and worse, that you describe. Mine would cut out and not fire again for a good 5 mins and repeat every few miles regardless of speed, engine temp, driving style ect...

It would only do this when the return was connected so I sent the fuel line direct to the carb and bypassed the swirl pot/return pipe. Was hunky dory after that. So you can run these engines without a fuel return fine.

[Eurobox]

No I don't have the swirl pot either now that you mention it lol. So it's just fuel feed straight to pump and from there direct to the carb. Thing is I can't understand why the fuel filter isn't full?

[Risocco]

Yeah, that's the set up I ran, with the return connected to the swirl pot, and the short hose that would go to the carb looped over the two remaining swirl pot inputs.

The filters are never that full of fuel are they? To be fair its been a while since I seen a single carb/mechanical pump set up.

[MacColl]

Have a read of this..
http://www.vwgolfmk1.org.uk/modules.php ... uel+return

and this..
http://sciroccoregisterforum.co.uk/carf ... 12&t=12885

When I fitted the Weber I kept the swirl pot and have now pressed a small cm length of vac plastic tube (around 1.8 mm inner core) into the plastic clear return pipe. This restricted the flow back and I think has increased the pressure. The kind of bogging I get at high revs/second butterfly has reduced and when starting from cold it isn't as intermittent when I drive off. I actually think more restriction might be necessary going by that Mk1 Golf forum thread.

I am also going to buy a fuel pump soon. If you don't mind me asking where did you purchase yours?

[Eurobox]

I got it from a local motor parts shop.

I think as above mentioned I'm going to take off the fuel line to the carb tomorrow and crank it over to see what flow I have, if it's ok (which I'm doubting looking at the filter) then It might just be a case of messing about with both the mixture and idle screws until I get it right, but I am just expecting to see a trickle really.

I've had thoughts of fitting an electric fuel pump and bypassing the mech one, would this create too much fuel pressure for a carb or wouldn't it matter?

[Eurobox]

Ok I pulled the fuel line from the carb and stuck it in a jug to catch the fuel and it was flowing well, in fact more couldn't have came out and the fuel filter immediately filled up aswell weirdly, possibly because I'd 'primed' the system perhaps? So fuel starvation theory is now out the window!

Anyhoo I'd also replaced the fuel filter and it's still full after a half hour run out but it was idling at 1200 rpm so I got it back and set the idle speed to just under 1000 rpm and when I run it now it starts to hunt again, so started to mess about with the mixture to try to get it to run just so at the set idle speed but no joy.

When I drive it at say 70mph on motorway and dip clutch it settles to about 1000 rpm and holds, but... if I'm just knocking about round the doors at low rpm's it starts to hunt about 500rpm then dies, wtf?

Is this either a case of getting the mixture and idle speed just right or could it be coil - rotor arm & dizzy cap could do with a change?

[Eurobox]

Anyone?

[MacColl]

Leak at base of carb? maybe just needs all tightened up or maybe needs a new rubber base plate as the quality varies. I'd probably buy one from here when I need one..
http://www.vwspares.co.uk/product_info. ... cts_id=812

Is the adaptor plate all nicely sealed on there, I have put a bit of hylomar on mating surfaces but not where the actual carb attaches.

Has the Carb had a service?, floats set right?

Dirt effecting carb from the filler neck? tank? metal fuel lines? collapsed rubber fuel lines? little fuel mesh in carb inlet that is better removed.Have you cleaned the jets?

Use the search engine and you'll see various scenarios and fixes that people have had with the same set up. So many subtle things that can cause these problems.

Very nice looking car by the way, just seen it in the Mk2 section

[Eurobox]

Yeah got the car looking just as I wanted last week, now just got to get to the bottom of this running issue, I'm pretty sure I'm almost there, but you know how it is lol.

I've pretty much been over all that stuff that you've mentioned, I even removed the little gause element from the inlet even though it looked ok.

I've checked for leaks around the base with the car idling, I've physically wiggled the carb left to right and back and forth to see if I could get a change in engine tone and given it a good spray about the base with wd40 but nothing so I'm pretty certain there are no leaks at the base.

Full system cleared out, filter changed and when I stripped the carb I blasted carb cleaner throughout it even though there wasn't a spec in it, so now I'm just going to change the coil, dizzy cap and rotor arm as a matter of course, at least that will be illiminated from my investigation and you never know, it might just be the cause.

I'm pretty sure the fuelling is adequate, base idle set (around) 1000rpm and mixture I turned fully in clockwise then back two full turns so I reckon that'd be enough throughout the rev range?

If you think of anything else I might have missed though...

Cheers!

[Eurobox]

Had the dizzy cap off to have a looksy and this doesn't look right does it?



So I've gone ahead and just ordered up a new Coil, dizzy cap and rotor arm so I'll see what happens when I fit them. Even if they arn't the cause they're all looking old so it can't hurt to change them while I'm tinkering anyway.

Also I removed the air box while the car was running yesterday, and when I removed the vac hose that runs from the back of the weber to the air box assembly the idle speed immediately picked right up and if I plug it back in it struggles again, should it do that, and whats it for?

Could I have some kind of blockage in whatever the hose is connected to, it looks like a one way valve or something?

[fonzooorooo]

with a weber, run the vac line directly from the dizzy to the carb.

Take the feed to the airbox from the niples on the 1 way valve on the vac line to the brake servo.

oh, and no... that dizzy cap does NOT look right!

[Eurobox]

with a weber, run the vac line directly from the dizzy to the carb.

Take the feed to the airbox from the niples on the 1 way valve on the vac line to the brake servo.

oh, and no... that dizzy cap does NOT look right!

Ok thanks for that mate, the vac advance hose is currently going to the brake servo pipe, today I removed it and it seemed to run perfectly, so that needs to go to the nipple at the back of the weber and the airbox assembly hose to the servo pipe, finally some good advice!

I'll do that tomorrow, thanks!

[Eurobox]

Ok so quick update...

Refitted the vac advance to the nipple at the back of the carb and connected the air box nipple to the one way valve on the servo booster pipe.

Took it out for a run and still I was getting the hunting at around 500rpm sometimes. Then I noticed that if I drive at any speed and dip clutch the revs drop to around 1000rpm and hold (happy with that.), but if I brake and dip clutch it drops well below 1000rpm and struggles to stay running until I lift off the brake, so it only does it when I brake. Then I also noticed that the hard plastic pipe that connects the brake servo to the one way valve had a slight kink in it, so I opened it out with a pair of pliers and fitted a fuel line jubilee clip around it to support it and keep it from kinking again and this made it slightly better.

Now the questions....

Is it possible that the one way valve in the servo booster pipe might be knackered?

Also I fitted a transparent vac hose between the air box and the one way valve and I noticed that a liquid was coming through it (from the one way valve it's connected to) slowly so I pulled it off the air box nipple and it turned out to be petrol, should this happen and would this also point to a dodgy one way valve?

Or am I barking up the wrong tree alltogether and is this 'almost stalling caused by heavy braking' symptom caused by something else and how can I fix it?