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

[fonzooorooo]

There shouldn't be petrol in the vac hoses(!)

Try whipping the air box off altogether,(you could cable tie the filter in place) and blank the small diameter vac pipes at the 1 way valve.

Check the breather pipe from the cam box is clear/not collapsed/full of grot/whatever.

That could help eliminate some stuff.

Do you know the ACTUAL fuel pressure at the carb? If not, could you find out?

[Eurobox]

I wouldn't know the fuel pressure at the carb, but if I take the hose off and crank it over it's got really good flow because I changed the pump and there is no swirl pot, it's just a hose straight from the pump to the carb.

All of the cars idling issues are gone now apart from the revs dropping under braking so I'm starting to think the one way valve from the brake servo might be leaking?

I wanted to remove the airbox and fit a K&N bolt on filter but I couldn't find one that would fit the weber and fit under the raintray. I bought one a while back on eBay decribed as fits all weber and pierberg carbs but it wouldn't go on because it was too high.

I've thought of using cable ties to secure the stock filter in place so I'll just do that for now until I can find a nice shiney new K&N that'll fit.

[bengould]

Just to throw a spanner in the works.

I have the vac advance coming from the one way valve to the brake servo

And the airbox feed coming off the Front of the Weber.

The one at the back has a little cap on it but can't get my beast of a camera in to take a shot of that one.

And I think by the sound of it it could be related to the one way valve. Take it out and try and blow through it, you should only be able to blow one way.

[bengould]

Although....

After actually reading the Weber fitting instructions

The Air filter feed SHOULD go on the back of the carb.


But the Vac advance bit was right.

[Eurobox]

Hmm yeah right so you're saying the vacuum hose from the back of the carb to the air box and the vac advance to the one way valve? I'll do that then.

Up to now I've pumped the fuel lines through, changed the fuel pump and filters, stripped and cleaned the already clean weber and replaced the entire ignition system and the problem still exists - idle sometimes 1200 rpm, sometimes 1000 rpm and sometimes under 1000 hunting eventually dying unless I blip the throttle a bit, also braking has an adverse effect. It sounds every bit like a leak at the base of the carb but I havn't been able to detect a leak with the wiggle test and I've blasted all round the base with wd40 and both tests didn't effect the idle so I discounted the rubber mount.

Sooo I'm going to replace the one way valve on the servo assist pipe and if that has no effect I'm just going to change the rubber mount just to eliminate that for sure.

Then if the problem still exists after that I'm chucking in the towel and taking it to a specialist tuner.

Question... Whats the optimal setting for the mixture on the weber?

Can someone confirm I've got this about right please... I turned it fully clockwise until it stopped then turned it back counter clockwise 2 full turns.

Does that sound about right or am I way off? It's just that when I changed the plugs they were sooty and stunk of fuel so it's making me think the problem might be down to too rich a mixture?

[Eurobox]

Ok so today I refitted the vac advance to the one way valve and the rear nipple to the airbox assembly. Then (with engine idling) when I dropped the bonnet it sounded like the revs dropped momentarily as it slammed shut and I immediately noted that it does this everytime I drop the bonnet with the engine running and never really thought anymore about it, but today it dawned on me that it might be because the airbox is touching the bonnet and it's making the carb jolt a bit... and you can see where this is going!

So, I really pushed the carb to the left as far as it would go and I could see a split in the rubber mount and started to die as it was drawing in air, then when I pulled it back over to the right as far as it would go it idled normally, better than normal actually so there it is, I've overhauled the entire fuel and ignition system and it was all down to the rubber mount leaking. So I'm going to order one up tomorrow and until then I've cable tied the airbox to that handily placed bracked that would have held the vacuum ball for the old Pierberg and this is keeping the split closed for now.

I'd previously wiggled the carb before but not really gave it a good hard rock left to right so if I'd done that in the first place I could have saved myself hours of head scratching, but at least I've gotten to the bottom of it eventually.

So if you've searched this and have similar problems and have discounted the rubber carb mount from your investigation because it seemed ok, then for god sakes change it anyway!

Thanks for all your advice and suggestions chaps, it's been educational.

[go-for-it1]

But why is the carb touching the bonnet when it is shut? The engine rocks naturally by rotational torque hence you have rubber mounts to dampen it out but it still moves, the carb and airbox should move with it so if your airbox is touching the underside of the bonnet, the carb will be held in one place whilst the rest of the engine below it will still move. Simply, if you don't allow the carb/airbox to move freely with the engine then the new carb mount will fail like the existing one, so you need to find out why the airbox is touching the bonnet and cure that first.
Rob

[Eurobox]

Hmm I just put it down to the weber being taller than the Pierburg?

Oh and I found a rubber carb mount for the weber after a search on here and also found the Euro Car Parts part number: 344440040

So I've gone ahead and ordered that.

[Eurobox]

Ok so I've fitted the new rubber carb mount and the problem STILL exists.

Just to refresh on the problem..

The following are at peak running temperature with choke fully in...

If I drive the car and dip clutch the revs sometimes drop to either 1200rpm or 1000rpm, in either case the revs eventually settle to around the correct 850-900 rpm and holds.

If I drive the car and dip clutch whilst braking (as if to stop for a red light for example) revs drop right off to about 400/500 rpm and after a bit of hunting dies.

So this problem is I think linked directly with braking, so the next step is to replace the hose and one way valve that comes from the brake servo to the inlet manifold, there's got to be a leak somewhere here be it in the actual hose or the one way valve.

This is my last effort to get to the bottom of this problem, not because I'm sick of it (well I am) but because I've done everything else, there's nothing else it could be.

And if this doesn't fix it I'm either going to sell it or break it.

[MacColl]

Don't give up with this, I'm sure there will be an explanation. The one thing that my Weber consistently does once it's up to temp is idle really well but I think it still has issues at higher revs or simply needs tuning.

Off the top of my head floats maybe set at wrong height? or trapping? fuel starving or opposite? a spec of dirt or fluff that is moving back and forth into the jets when you brake?? I'm baffled to be honest, maybe what you describe a vac issues from the brake servo.

I would maybe have a good search round the likes of CGTI or the Mk1 Golf forum maybe someone else has had an issue, or post a question up on there.

Anyone you know that could put a fresh pair of eyes on the situation?

I remember having loads of issues with the weber on my last Scirocco and even though it was fixed I never really found out what it was?

Good luck

[Eurobox]

I called into my local VW main dealer for this assembly and it was discontinued in 2005.

So I'm either going to have to source a new vacuum hose the right size and a replacement one way valve that will also fit the joining hose to the inlet manifold or try to get one from a breaker.

I can't see obtaining a one way valve with an additional vac nipple on it for the vac advance being easy, so might have to chuck a T piece inline before the valve, I can't see why that wouldn't work the same?

Or... do I really need the vac advance? Can I still run without it?

[MacColl]

Sorry I wasn't grasping that you had found the possible issue with the vac hose last night half asleep

This is how it looks on my car..


I might have spares from my old Scirocco if you're stuck but won't be near my workshop till Friday.

[Eurobox]

Sorry I wasn't grasping that you had found the possible issue with the vac hose last night half asleep

This is how it looks on my car..


I might have spares from my old Scirocco if you're stuck but won't be near my workshop till Friday.

No I was suspecting that anyway, but...

Today I removed the brake servo assist hose and tested it and there were no leaks, so it's perfectly fine.

I can blow through (from servo to inlet mani) but can't the other way which tells me the valve is working properly.

So thats now eliminated from my investigation and now I've exhaused all possibilities to my knowledge so I'm totally baffled.

[go-for-it1]

Having looked at the pic of your carb with the airbox pipe coming off the front and then looked at the pic of G60MAT's recent carb purchases in "Pierburg (Zenith) Woes - it just won't start!" (the one with the manifold connected), your carb looks like it is the same as a golf mk2 1.6 which may be a possible cause of your running probs if the jets are not correct, and height issues where it is touching the bonnet. I have a weber fitted which I bought new and there is no pipe on the front of the carb where yours is and it does not touch the bonnet.
Rob

[Eurobox]

I havn't posted a picture of my carb, that was bengould's. I was wondering what that wire was for because mine doesn't have that.

I'm starting to look back at the carb now, it's now the only thing it can be, but what?

My new theory (as afore mentioned about the float height) is that when I'm braking the fuel in the chamber is going forwards resulting in the floats dropping and closing the jets causing it to ilde low and die? Does that sound a possibility?

How do you adjust the float height?

Or is it time to hand it over to a specialist tuner?