Havent found a garage that knows what this is yet, can anyone help? (Weber Carb)

Hi everyone, newb here so all advice appreciated.

I have a mk2 Jetta 1.6 fitted with a 32/34 weber
The problem really is having low power and the car not wanting to rev over 4k rmp. I'm trying to work out whether this is a problem with the carb or with the engine or what.

Whenever i put my foot right down and open the second throttle valve on the carb, the car drops revs and loses power, which is the opposite of what's meant to happen! Then when i keep my foot above that level, just opening the first throttle valve the peak power feels at about 2,500 rmp. nothing above that.

I took it down a 'classic vw specialist' and we had a look at it and found out by revving it that when the second throttle valve is opened, fuel and air is actually blown out the top of the carburettor.

I was thinking that whatever is causing this would be the root of all the other problems!!

I would really like this fixed as the car is returning about 20mpg at the moment with no power to show for it.

I have also changed the carb flange to be sure it isn't sucking in air under the carb.
Compression test was all ok as well.

Thanks for reading, any help would be appreciated!
I can't seem to find anyone else ever having this problem.

Lawrence.

 

Try Barry Symons in Maidenhead : http://barrysymons-garageservices.co.uk/
He stripped and rebuilt the carb on my mums mk1 and replaced the carb on my mates mk2 driver.
If you need replacement carb parts then try the carburettor hospital : http://www.carburettorspecialists.com/
Have you changed the big thick base gasket?

 

Thanks for the reply.

Yes, I have replaced the carb flange between the manifold and the carb.
I have been recommended to strip the carb before, but i bought it new, it's only done about 2000 miles. Surely it wouldn't need doing? It did sit for a few months, but i have cleaned out all the jets, could leaving it to sit cause this problem?

 

Does the accelerator pump jet work correctly?
This is the 'r' shaped piece that points down the barrel of one of the venturis. It should squirt a mist of fuel once (into the carb - not out of the top) when the accelerator is pressed hard. It operates via a pump diaphragm on the front of the carb which is connected to the vacuum system of the car. Its job is to provide extra fuel for when teh change over from one butterfly to two occurs and prevent bogging down.

 

It sounds like its running very lean. Has anyone done a CO check via a pipe up the exhaust? My bet is it's only reading very low, that's why higher in the revs with the second flap open it's down on power as there isn't enough fuel to mix with the increase in air. Do you know what size jets are fitted?

 

Thanks for the advice, I will go out and check that now, would that still cause it to be low on power without the second throttle valve is opened.

Thanks Dan, I did have it set up by my local garage during my MOT to 3.5 CO. But it was still running poor, so i took it to a 'classic vw specialist' who set it up by ear, without a CO meter. Could it running lean cause such bad MPG return though?
I'm not exactly sure on the jet sizes, but i bought the carb new from Fastroadcars to fit my size engine, so they should be right? Thanks.

 

Are all the vacuum connections connected properly and the pipes not damaged? Look here:- http://www.clubgti.com/showthread.p...old-air-flap&p=1339810&viewfull=1#post1339810

Does the vacuum advance on the distributor work as it should? Test by sucking on the pipe and putting it on your tongue (it should stick with the vacuum that you sucked in).

Fastroadcars are helpful, if you bought new I'd consider having a word with them.

 

I have just checked, and it appears to be working, when the car isn't running a mist of fuel is released when i open the second stage throttle. Thanks for the suggestion.

Yes, all the pipes are connected correctly. I have used some 4mm fuel line as it's what i had around, but it seems to do the job fine for now.
I have just done the vacuum advance test and yes, it does work. Any other suggestions?

I did speak to the guy there before, but he wasn't too sure and just suggested a garage to go to. Hoping someone on here may have had the same problem, can't really afford the garage time to find the fault. Thanks.

 

Has the weber just been fitted? If so was it running ok before? Has the timing been checked?

 

It was fitted this time last year, it wasn't driven with it on. I then refitted it when i brought the car back on the road in January with a new carb flange.

I have set up the timing with a light to the mark on the flywheel and it advances accordingly as the engine revs. Thanks for the suggestions.

 

sounds to me like cam timing is out if its blowing fuel and air out the top of carb, compression coming out, check timing marks and do a compression check would be my 1st call mate

 

infact my 1st mk2 1.6 driver had these exact symptoms and the timing had jumped.

 

Thanks for the suggestion. Do you mean that the timing on the camshaft could be out by a tooth on the belt? Was that your issue?

 

exactly

 

Brilliant! Thanks so much for the advice! I'll try this tomorrow, and I owe you a case of beers if you're right, I've had loads of different suggestions, but most of them involve spending hundreds at the garage, or rebuilding the head of carb. I'll let you know. Thanks.

 

I just wanted to ask, before I pull off my timing belt, when you had the same problem, did the car run? The car does actually run at the moment and idles fine, just low on power and fires back through the carb at high revs, surely the symptoms would be much worse than that if i was a tooth out? I just wanted to ask before I mess about with my timing. Thanks.

 

I wouldn't pull the belt off just yet, just get the engine to TDC and make sure the timing lines up as the pic above.

 

Thanks, yes. That was the problem. It is now resolved. It's been running like that for weeks! I think my mistake was when i changed the head gasket, I got it a tooth off by using the mark to line up the camshaft to the front of the head. I aligned it with the mark on the plastic back plate this time. And it's now so much better! It actually pulls. Now i just need a gti camshaft in it.

Thanks everyone for your help.

 

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