Weber setup

[Brenjacques]

Hi all

Getting through the work on the scirocco, I sorted the ignition timing a few days ago and that is all as it should be now so I'm turning my attention to the recently fitted weber 32/34 that has been fitted.

It's been pretty good and I've had it on the car for about a month, but adjusting the timing (which was quite far out) and the colder weather is springing up some problems. Last night I reset the idle speed and mixture and that is fine, once the engine is warm it goes as it should.

The problem I'm having now seems to be with the choke, when I cold start and pull the choke full out it revs at about 2000rpm and I adjust it to around 1500 pushing in more as I drive. There seems to be some kind of flat spot where the revs are dying down as the engine warms up whilst the choke is still being used. The only way to stop it from bogging down to much is to use the accelerator to hold the revs up when stationary and use a bit more choke. As the engine warms up more it starts to dissappear and when the engine is fully warm and choke is fully in it is fine.

From the smell I'm thinking that it is over-choking and not enough adjustment on the choke throttle screw. This lunch I started it up and adjusted it out of bogging down as it warmed up by applying more throttle and less choke. It seems to have done the job but it looks to me as though there may now be too much on the throttle and not enough of the choke flap closing.

I'll be readjusting it over the next few days to find the best point of choke flap to throttle adjustment but in the mean time does anyone have any further advice on what to look out for?

Forgot to add that if I pump on the brake pedal when it's dropping in revs, they rise back up... Possibly a symptom of it running too rich on choke?

[chopperoli]

Your last sentence makes me wonder if you have a vacuum leak? Since brake servo and choke pulldown are both vacuum operated. The pulldown backs off the choke flap by a set amount, maybe that is not working, leaking or incorrectly set, as well as your fast idle was?

I really recommend the Haynes manual for Weber downdraft carbs, ISBN 185010784X

[Brenjacques]

I'll have a look for any leaks but as far as I'm aware there aren't any. If I'm thinking correctly, if there was a fault with the pull down unit then surely that would cause problems on initial start up after the engine has been running for a minute or so as you'd need to have the choke out a fair amount for the valve to be able to shut fully.

If it is related to the pull down unit then maybe it is incorrectly set or faulty being as it is happening after 10 minutes of the engine running.

I'll have a look over the weekend and watch it start from cold and see how well the pull down unit is working and if this is affecting it. Probably also get some photos of how closed the choke valve is at different revs to be sure that it isn't too open.

[chopperoli]

If you do have a leak it would also be affecting vacuum advance on the distributor, which might better explain the idle dip etc. The diaphragms on all these things can fail over time, especially with modern petrol vapours attacking old rubber. A Mityvac is priceless if not essential for problem solving. Good luck!

[Brenjacques]

Thanks, I'll take a look at it as soon as I can. Had the same problem on the way home from work despite the adjustments I made earlier. It's just strange how it's during a particular time of the the warm up, almost when the temp gauge is between cold and half way. It's fine before then and once the engine is warm it performs with no problems.

Also, with pumping the pedal it only raises the revs when the choke is on and during this period of rev dropping. When the car is warmed up and choke is off then pumping the pedal makes no difference to the revs.

[james butler]

yup like choperoli said if pumping the brakes changes the idle you have an air leak or the vacuum check valve has failed.
the choke on the weber isn't very sophisticated and is heavily linked to your current mixture setup.
due to the nature of the weber being very fixed when you tune it the carb will be very sensitive to changes in the environment you drive it in.
essentially you need to tune it either in spring or autumn on an average day, you will find it will run a little worse in hotter summer days and colder winter days but best in spring and autumn.
it is normal.
one factor that can alleviate the issue is making sure the air intake hot and cold feed works properly.
one last thing i can't stress enough, make sure your rubber carb flange is mint. they split along the seams which is very hard to spot when they start going.
most people don't notice until the carb pretty much falls off.
these are great carbs and don't usually need much messing about with to get working great.

[Brenjacques]

Thanks for the advice, I'll have a look tomorrow and make sure that everything is fine. The carb flange isn't that old, I only fitted it last year but I'll give it a check and see if theres any damage.

Regarding the hot/cold air intake, is is possible for this to cause similar problems say if it is sticking or if the vacuum pipe has any air leaks, has a split or the rubber ends are worn? I only ask because it really does feel and smell like over fuelling. I almost got a bit of run on when turning off after parking it at work today.

Reading more online I wonder if this could be a sign of the carb icing up now the weather is getting colder, its been fine on this weber up until a couple of weeks ago really.

[Brenjacques]

Had more of a look on my lunch break, the cold/warm air flap is seized solid in the cold air position, so I need to sort that. If I remove the vacuum hose from the rear of the carb to the air box the idle rises, once refitted it drops back down. It also does the same when it starts running lumpy with low revs, if I remove it then it raises and smooths out. Does this still sound like a vacuum/air leak as introducing a vacuum leak on this pipe seems to sort the problem.

[GT_II]

The cold air intake can certainly cause carburettor icing during cold weather, which tends to make it run rough and stall when warming up. I remember this fault on a 3 year old 1986 Polo I bought 2nd hand many years ago. At that time I was a bit of a parts swapper, and changed several ignition parts without success. Luckily, I happened to speak to the parts manager at a different dealership, who suggested I check the vacuum operated intake flap. I had a look and found the operating lever for the flap was disconnected inside the intake tube, so always open. Reconnecting the lever fixed the problem.

[Brenjacques]

I think icing may be the problem, at least part of it anyway. After work I drove it home slowly and keeping the revs low and it was fine most of the way home, on the last few streets I floored it a bit more and by the time I was pulling up it was almost stalling. Also noticed the garage that fitted the weber haven't swapped over the carb heater, it's still on the 2e2 that was removed so this certainly won't help things.

I'll free the flap off tomorrow and fit the carb heater and see how that improves things. Can anyone tell me which is the correct plug for the carb heater as I wouldn't have an idea myself and there's obviously a few leads left over from the 2e2.

Cheers
Bren

[james butler]

check all your vacuum lines and the carb flange.
it may be that your carb hasn't been running properly before you got it and someone has increased the fuel mix to compensate.
before messing with the fuel mix however make sure the car is mechanically sound

[Brenjacques]

I'll give it all a check today, I'm in the middle of sorting the hot/cold flap and carb heater now. Is there any other adjustments for fuel or air other than the idle mixture screw? I ask because it runs so much better with the rear vacuum hose disconnected, I wonder whether someone set it up with that removed and then fitted it afterwards causing it to have this problem.

[Brenjacques]

Just an update, cold/warm air flap is now free and working and the carb heater has been fitted to the weber. Took it for a long drive in the cold and no problems at all now so I presume icing was the main problem.

I'm having a mobile carb servicing/tuner come and do a final tune up on the carb and hopefully that will have it going as it should.