Weber carbs out of control or....?

[porschepalle]

Hi.
The engine with Weber carbs and idle are OK the first 20 min. when I take a drive on the highway. However, hereafter the (warm) engine goes up to 3000 rpm without touching the accelerator pedal. When I stop and then immediately restart the engine it goes up 2500-3000 rpm again. In cold condition the engine behaves normally (idle at 1100 rpm). I cannot solve this problem - what about you my friends - can you help me (again) ?

Regards

[Peter Graham]

Try setting your idle speed between 850-900 rpm with the motor warm; this may not support cold idle (which can be fixed by richening idle mixture). I believe the problem may be that your ignition timing is advancing when the motor is warm. While Webers will work on a 912 out of the box , they require work to get properly set-up including changing venturis (come with 28's; need 30-32mm), emulsion tubes (come with F11's; need F7) and jets. There are extended discussions about Webers/Solexes on the 912 BBS: use the 'Search' function.

Peter

[porschepalle]

Thanks a lot Peter - I'll work on it as suggested by you.
Palle

[JT912]

Could be related to the advance on your distributor too. Sticky weights?

[porschepalle]

OK/thanks John - I'll check this.
Palle

[NICE 69 S]

When the idle gets to 3,000, look at each carb and see if the throttle stop is sitting on the idle adjusting screw. If not, grab the throttle arms on each carb and see if you can return them to the stop. I don't know of anything in the carb that could cause the idle to go up when they get hot. Seems to me that it is either a distributor problem, as mentioned above, or sticking linkage keeping the carbs from returning to the closed position.
Bob B

[porschepalle]

OK/thanks Bob - I'll check this.
Palle

[ganun]

IDFs .......Check that the choke is not stuck on, they must have a choke.
but the links below are a good start


http://civilianjeep.info/Strenk/Carbs/WeberIdleTransfer.gif


IDF Adjustment Controls

[porschepalle]

OK/thanks George - I'll check this, too.
Palle

[porschepalle]

Hello again ....

By setting the idle speed between 850-900 rpm with the motor warm solved the problem re very high idle rpm (>3000). Thanks

However, when the motor runs warm it sounds and feels as if one cylinder drops out: less power and more vibrations. When the motor is started in cold condition later on, it runs relatively well, i.e. the car accelerates swiftly to 70 mph. - and then the problem starts over again. It may happen that the motor suddenly gets its power back and then again lose it - an on-off symptom.

I am aware of the fact that one symptom may have different causes. Does the weber deliver too little fuel to the engine after running a while, or...? What do you suggest?

Regards Palle