Carby troubles

[doridori]

Hi, if anyone could help....

4age 16v with cams and twin Weber carbs...

I have a flat spot in the rev range at around 2300-2500rpm, the engine stutters and struggles... Why?

Really temperamental problem. As in it comes and goes seemingly whenever it feels like it. I can't really see a relation to cold changes in outside temperature either.

Had a look at the spark plugs and the back set of Weber's are running much richer than the front set and have much more residual petrol sitting around the top of the set (checked that all the jetting is the same). Why is this and how can I fix?

Is this a timing problem, jetting, fuel pump... ? I don't know...

Any thoughts would be great...

[Jonny Rochester]

The front and rear carby both have to be in sync in a few different ways.

Bur first, the carbys have to be sealed to the manifold with no air leaks. And the linkages in good order with no movement or slop.

The throttles have to be balanced, so both sets work together perfectly. One way to check is to let the engine idle, and play around with throttle adjustment, have a think/listen about what your doing, and make it so both sets have the throttle cracked open the same amount. The other way, is to hold then engine at medium revs, and check the air flow, with a air flow meter over each intake. Another way is to have the engine at medium revs, and check vacuum pressure in each runner. This will work if you have a vacuum port in each runner, and the balance tubes are blocked off. Make adjustments with the throttle linkages.

Also, you have to check the fuel level is the same in either carby, and adjust this. If you take a main jet holder out, you will be able to see how high the fuel level is. The carby running rich probably has a higher fuel level, which could be due to adjustment, or a faulty needle and seat.

[doridori]

Thanks for that mate... I'll try and see what happens...

[doridori]

So they are both in sync, (not *nsync) yet still the prob.

Could this be a busted float pin?

[blair]

Just to clarify, your not fully opening the throttles at those revs?

just normal driving below 20km/hr?

[doridori]

Thats correct. Not fully open.

There is a little bit of fuel coming out of the venturi's and quite a bit sitting on the top of the rear set too.
I can now hear the fuel pump going a bit harder. which leads me to believe that the float pin has broken and the bowl is constantly filling when it doesnt need to, causing excess fuel coming out of the venturis and general richness ....??

Thoughts?

[fatke]

wat size cams r u running? if they r pretty big cams u can not drive the car half throttle it needs to be constantly up in revs

[doridori]

Cams aren't huge, very drivable in the past , so this is a new problem that has slowly come on in the past 2 weeks

Economy has gone to shit too... (obviously)

[Jonny Rochester]

Undo the wing nut and take the round jet cover off both carbies. They are not needed to run the car just testing it. Unscrew one of the top air jets, and unscrew the whole jet holder (long tube) and take it out. The car shoud still idle like this, but you can look down the hole and see where the fuel level is. Do the same with the other carby and compare levels. I would expect the fuel level to be about 20mm below where the air jet should be. Some carbys have an external fuel level adjustment, with others you have to pull the whole top of the carby off, and bend a metal tag or something.

With Webbers, they have brass floats, which are known to sometimes puncture and fill up with fuel.

[fatke]

yeh they fill up they dont cost much 50 bucks