Quote:
Originally Posted by jhirasak
Hyde,
Thanks for sending your latest jetting spreadsheet to me. Just as a point of interest, I would like to mention the jetting and other changes that I had to make to a set of brand new 48 IDA Webers (out of the box from Redline) to get them to run smoothly on my car. They are as follows:
1. Adjust each float needle height to 25 mm by sanding the needle seat gasket (found a difference of up to 1 mm between the four carbs)
2. Adjust each float height setting after normalizing needle seat height
3. Adjust each carb air flow with butterflys closed so they indicate within 1 unit of each other reading on the air flow syncro meter (the general recommendation is to twist the throttle shaft to get the two throats to read the same value. I chose to drill small holes in the butterflys to get the same reading on all of the carbs)
4. Decrease Idle Jet holder from 120 to 100 to cure off idle transition hesitation
5. Adjust idle mixture screws to 1 1/8 turns from closed (different taper on idle mixture screw than earlier Webers?)
6. Change Emulsion Tube from F7 to F11 to correct for main jet transition richness (found problem by use of wideband O2 meter)
7. Change throttle linkage from as-provided single cross link to a bell crank arrangement to correct for left bank to right bank throttle position error (with single cross link arrangement, if both bank flow the same amount at idle, they would flow significantly different at 1800 to 2000 rpms, linkage geometry problem)
8. Change accelerator pump exhaust valve from 00 (blank) to 50 to correct for fuel dripping into the cylinders after hot shutdown (problem made worse by recent addition of alcohol in pump gas)
For anyone planning to install Webers on their car, I would highly recommend that they perform the first three steps listed above [u]before[u] they ever install them on the car for the first time.
John
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John,
I beg to differ on point 8.
The exhaust valve with a STEEL inlet checkball is OPEN at rest so will not allow pump well pressure to overcome the pump nozzle outlet check ball, even after hot engine shutdown.
The nylon ball exhaust valve MIGHT have your mentioned phenomenon, but more than likely the carburettor is percolating. Solving the percolation issue is usually the best way.