Posted by Chris (216.172.142.47) on March 12, 2001 at 04:19:53:
In Reply to: carb problems posted by Maverick73 on March 11, 2001 at 19:26:09:
First, that carb is to small for your engine. It will work but be harder to tune. I would try a 750. This is not just because it flows more air either. The larger carbs are calibrated for more radical or larger engines. It's the internal metering calibrations that make the difference (not the jets or P.V.). I'm talking about the idle, power valve, and fuel delivery circuits. Whatever carb you use, try this:
1) Hook a vacuum guage to one of the full vacuum ports on the carb.
2) Warm the engine up and try to get as stable as an idle you can.
3) As a starting point, check the idle vacuum to make sure your power valve isn't open at idle. The P.V. rating should be about 2" below your idle vacuum. (ex: 6" of vac. at idle, use a 4.5 P.V.) Or if you have a P.V. plug, use it for now.
4) If you have driven the car enough, hopefully, the jetting is close to correct already. If not, try to get it as close as you can for now. Up to a point, the jetting will effect the idle mixture adjustment! The fuel supply for the idle circuit is behind the jets. The larger or smaller the jets, the more or less fuel flows into the metering block and through the rest of the carb.
5) Turn the idle speed screw up or down to get the idle down to around 1000-1200 RPM's. That's really a guess, every motor acts and idles differently.
6) Adjust the mixture screws until you get the highest amount of engine vacuum.
7) Then readjust the idle speed and recheck to make sure you have the correct power valve. If you used a plug, replace it with the correct P.V. now. You can also go back and check your timing too.
Also, if adusting the mixture screws has no effect, that's one of the signs you don't have the correct carb. With the smaller carb, it will also be harder to tune the secondaries. The top end is always going to lean out.