weber tuning
 

OK, so I got hold of a unisyn and I was trying to balance the carbs. I got numbers 4 and 5 fairly close but number 6 is alot lower. No matter what way I turn the air correction screw I can not bring it up to match the other cylinders. Anybody have any ideas on this or a procedure I should follow. Is it very important to have the timing set with a light before touching the carbs. It seems to be fairly close and I'd like to leave it another while so that the engine is well broke in before I bring it up to 6000 RPM.
thanks for any advice
Martin

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Martin
'70 911T

I don't know if you know this or not, but it is important to have the throttle linkage rods DISCONNECTED from both carbs when checking/adjusting the idle flow.

Any cylinders showing remarkably lower readings MAY have manifold-gasket leaks (because the 'leak' is below the throttle butterfly, it does not suck as much air through the 'horn' where you are measuring the flow with the Uni-Syn) ... spray carb cleaner -- using the long 'tube' usually taped to each -- can be used to check for leaks at the gasket/carb/manifold junction. Any 'rise' in idle speed when spraying the carb. cleaner is indicative of a manifold leak at that manifold! You may need to loosen, then retorque the nuts holding the carbs to the manifold ... if that doesn't work a new gasket is called for.

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Warren Hall
1973 911S Targa

[This message has been edited by Early_S_Man (edited 06-30-2000).]

After trying the above, you might want to do a compression test and see if the #6 cylinder is weak. This could be due to valves out adjustment or some other thing that is making a cylinder weak.

Martin,

I had a similar problem with 3 cylinders running a much higher reading on the Unisyn. Warren had recommended the same likely culprits which checked out ok.

The true culprit was "user error" . When I rebuilt the Webers I did not take enough care in making sure the butterflys were replaced EXACTLY as they should have been. As a result the slight error in replacing the butterflys resulted in the throttle staying slighly open at idle. This made for skewed Unisyn readings. After it was corrected the car ran beautifully. Just a thought.
I'd also be sure the linkage is adjusted side to side and that it is disconnected during adjustment. Good luck with it.

Rich