Rough running under load

[Red Rocco]

Hi, I have a ‘91 GT2 fitted with a Weber carb, the carb was fitted around 3 years ago when I bought the car. When I’m driving and reach a speed of around 50-60 the car starts coughing and spluttering almost kangarooing! it seems worse going up hill. If I back off the throttle and slow down the problem seems to go away. I fitted a new fuel pump, hoses, fuel filter and filler neck last year and all has been fine since. The dizzy cap and rotor arm are good and so are the leads. I’m thinking this is a fuel problem rather than electrical, but could be wrong! Could it be a problem with the ‘carb flange’?
Help as this is my daily driver!
Thanks
Rob

[G-Dub]

Inside the fuel tank you have a lift pump. On the end of the pick up pipe you have a filter/strainer and these can block and limit flow at higher speeds. Could be worth checking out.

[Red Rocco]

Hi, thanks for reply
I did look for a lift pump, the only thing in the top of the fuel tank is the fuel gauge sender, I think only injection models had a lift pump fitted in the tank. Are there any other strainers or filters I should be looking for though?

[C 20 CCO]

I had a similar experience last year;
http://forum.sciroccoregister.co.uk/vie ... 06#p150496

I literally changed the fuel system bar the filler neck and tank. I have the 2E2 original carb still going strong....

My original carb flange of 26 years looked in great condition, but changed it as a matter of precaution. Eventually after 2 months of problems I had vapours / smoke rising from under the carb/ exhaust area, I changed the inlet manifold gasket and water seal and it’s been fine ever since.

As I say check or change fuel filter, unfasten the filter and blow back down the pipe to the tank. Just to check for blockages or restrictions. Keep us posted. We’ve all had issues.... some more than others . But still won’t part with it

[Red Rocco]

Thanks for the link. Been out in it again today, it’s fine if you’re just tootling along but as soon as you give it the beans and the speed increases it starts to cough and splutter. I think I’ll change the carb flange and manifold gasket as a matter of course, I did notice some greasy staining on the inlet manifold just under the carb so maybe this is where the leak is? Most of the fuel system bar the swirl pot and fuel tank was replaced last summer, although never rule out new parts!

[C 20 CCO]

If you've never done the inlet manifold gasket before..... it’s tricky but not impossible. Use the long Allen keys with a ball on one end, mirror, lamp and tongue out to one side of the mouth helps.
I got my parts from vw heritage.... I had more than stains to show there was a leak, looked like something was burning. Have you done a vacuum test on the fuel line? I started from the tank and worked towards the carb. Had there been a problem other than with the inlet gasket, a vacuum test would find it. Just a thought!

[Red Rocco]

Hi,
How would you perform a fuel line vacuum test? Would it be a case of removing the pump from the engine block with the hoses still attached and pumping the fuel tank hrough manually? I noticed the problem seems worse when the engine is warmed up, could this point to a dodgy ignition coil? I may aswell change the exhaust manifold when I do the inlet manifold gasket as there has always been a slight blow, so I can sort two problems at once!

[C 20 CCO]

Hi,
How would you perform a fuel line vacuum test? Would it be a case of removing the pump from the engine block with the hoses still attached and pumping the fuel tank hrough manually? I noticed the problem seems worse when the engine is warmed up, could this point to a dodgy ignition coil? I may aswell change the exhaust manifold when I do the inlet manifold gasket as there has always been a slight blow, so I can sort two problems at once!

Hi, For £12 I bought a sealey 80mm Vacuum and Fuel Pump Line Pressure Tester for Carburettor Fuel delivery systems. Tests Pressure Up To 10 PSI in fuel lines. Desperation was setting in and I was looking at all sorts of scenarios. I thought I had a leak somewhere in the pipeline from tank to carb. My inline fuel filter had hardly any fuel in it. Oh sure it filled up when the engine stopped as the fuel flowed back into it. So I started testing from the flexi pipe at the tank, working my way forward writing down the results on piece of paper against a diagram. The pump should be pulling around 0.2-0.25 bar or 2.9- 3.6lbf/in2. I was getting a low reading all the way so ruled out a leak in a particular section. I used brake pipe clamps to seal the pipe to get a reading.

I left the fuel pump in place when starting the engine because the reservoir had fuel in and so did the carb chamber. You can always do another test by disconnecting the fuel pipe from the carb. Disconnect the ht lead from the dizzy. I placed the fuel pipe from the carb into a bottle and cranked the engine to check the flow. It was a bit weak on my test.

It’s a very simple fuel system but I had to do a bit of head scratching, so just checking fuel pipes for leaks (air or fuel) or replacing the pump can be a fix.
In my case it was even harder to suss out, but changing the inlet gasket helped me. You seemed to be having the same symptoms as I had, mines a 91 GTii also. So what’s that.... about 28 years old!
50-60 mph and the fuel starvation showed up. If I kept running even at a slower speed it eventually ran out of fuel. It got that way I was tickling the throttle up hills, it just got silly.

If a new carb diaphragm was fitted with your webber carb, I doubt this would be a cause. Feel free to check it though as nothing should be ruled out. But I would definitely think about changing the inlet manifold gasket and water seal. Especially as you’ve already changed the fuel pump a little while ago.
Tricky one this..... Go steady, soak any bolts or studs in releasing oil and leave to penetrate. If you feel a bolt getting tighter as you’re undoing it, give a few re-tightening turns and work it back and forth to avoid snapping anything. The inlet bolt heads proved quite easy to get off barring the one nearest the battery. I got new bolts from a supplier to VW. See how you go...


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[mark1gls]

If taking any bolts or nuts off the heads exhaust side it's best to replace with new, they don't cost alot and make removal much easier next time. A good coating of copper grease also helps.

[jupiter8]

I have had a similar problem to this in the past, loosing power/rough running around the 50 mph mark. It was fuel starvation caused buy the needle valve in the carburettor float chamber being loose dropping down and preventing the float chamber filling.

Solution was to locktight and press the valve back in place, normal running restored.

[C 20 CCO]

How are you getting on? Have you managed to order your parts ok.


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[Red Rocco]

Hi, sorry it’s been a while! I’ve replaced the carb to manifold mount and the carb gasket, but problem still persists! I’ll check the carb float chamber needle valve next as that’s nice and simple job. I’m putting off doing the inlet manifold gasket for now as I want to rule out all the easy jobs first! Going to have a tinker with it at the weekend and I’ll let you all know how I get on

[C 20 CCO]

After reading other posts for needle valves, I too thought “hey that sounds just like my fault. My needle valve was in great condition, considering how old it was.
I went down so many dead ends before changing the gasket for the manifold. After I exhausting most ideas for remedy, I turned to the Haynes manual. And sure enough in the fuel problem section, a leak at the inlet manifold would cause fuel starvation.

I don’t want to steer you away from a fix especially as I haven’t seen your car, but it would be good to provide useful information based on my experience
Anyway see how you go, you never know!


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[Red Rocco]

Hi,
Gave the fuel hoses another check today, found that one from the fuel filter to pump was starting to collapse on the inside so I’ve replaced that, then found on the fuel filter neck on the incoming side was partially blocked with what looked like bits of paint. So all fuel hoses and filter now replaced, had a run up the M54 in it this afternoon and it runs really sweet!

I couldn’t see the blockage in the filter neck as it was covered with the hose, I think the bits of paint had got there from the old filler neck that I replaced last year, when I removed it I noticed it had been painted on the inside and it was peeling off. Fingers crossed no more will come through now

Thanks for all your help, turned out to be something silly in the end. The carb has been cleaned up with a new mount and gaskets so is all nice and clean now, so not a total waste of time!

[mark1gls]

Might be worth to have a spare fuel filter in the boot just in case and replace the one fitted in a couple of months as they cheap to buy, just to make sure there is no more paint flakes getting through.
I guess who ever painted the old filler neck did not use the right paint as normal car paint comes off when sat in petrol, not sure why they painted inside the filler neck?