Weber problems

[josh912]

Ok, I've just rebuilt my weber 40 IDFs on my 912 and what a difference. It idles and runs a lot better. However, I have a NEW dead spot at 4000-4500 rpm. It jerks severly and coughs until 4500 rpm and then it runs fine. My question, why is this and what should I do??? Thanks in advance.

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Joshua Harrison
1968 912 Coupe

[This message has been edited by josh912 (edited 04-22-2001).]

[iustasail]

My guess is that you corrected many problems by your rebuild; thus throwing the system out of balance! If everything is screw up on an engine it can be adjusted to run, just not well, and as you corect the work of the Turkeys the system goes out of ballance and the engine will run like crap! Check your jet sizes, they were probably picked to acomidate the problems you corected and are thus no longer corect; I would go with the standard set up and work from there.

[josh912]

Great news! The problem was a loose spark plug connector on the #1 cylinder. It came loose AFTER the carb rebuild, so don't laugh too hard.

I still have a flat, not dead, spot at 4000-4500 rpm but after that WHOA!!! This thing has A LOT of power! Then again it was built as a high performance engine.

Any ideas on the flat spot would be greatly appriciated.

Heres the low-down on the carbs
Weber 40 IDF 19
32mm venturi
4.5mm aux. venturi
50 idle jets
135 main jets
200 airs
50 pump jet
55 bleeds
F11 emulsions

Thanks for any help and suggestions and thanks to all who have responded already!


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Joshua Harrison
1968 912 Coupe

[iustasail]

What type of cam do you have?

If you are using a hot cam it should come on at around 4-4.5K so I would guess that you are having a transition problem! In my stock engine I was using 57.5 idle (actually they are transition jets as they do not greatly affect idle flow but greatly affect the transition to the main jets) so I think your 50's are small, especially for a hot motor. My 2.3L 911 engine in my 914 runs with 62 idle jets! It is ported and polished, 9.8-1 CR etc... So I can't help but think that your idle jets are causing your engine to go lean as it gets on the cam and then your 135 mains finally kick in bringing back full power. I would try 60's and see if the flat spot goes away.

[josh912]

Problem solved! The accelerator pump diaphragm wasn't sealing properly. The gas was leaking out and the floats couldn't keep up at high rpms causing fuel starvation on that carb. Now the car runs great, idles great, great throttle response, and has lots of power!

Special thanks to all who have helped me with this problem!! It was very much appriciated.

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Joshua Harrison
1968 912 Coupe