Originally Posted by hotboy454
Yes both carbs were running.rich. it ran smooth.but not as.smooth as.it should.be. I change to carb to summit brand still the same thing. Exhaust black and gas through exhaust. My wife hates when I start that thing up it get all in the house and the smell on my clothes. We tried idel mixture screws.didn't change. Thing. I almost thought that it qW the carb spaced drawing to much fuel. Tried 3 sets of plugs all are dark within days. The motor was broke in many months ago. It just sat untill I took the motor out and put it in my truck. Now its being driven under a full load. Oh by the way that's Joe gibbs break-in oil not Hubbard. My phone tries to think ahead of me.
OK, I see. In any event, I usually try to sort the timing out first, THEN set about fine tuning the carb. But in this case it sounds like something is amiss, like the fuel pressure way too high, that sort of thing. I say that because you've had two different carbs perform basically the same way. Odds are against that happening, but just the same, unless they are known by you to be jetted stock or at least within reason, I would want to baseline them (or it) back to stock to eliminate that from being the problem.
Someone mentioned power valves earlier. If it's blown or the wrong number it could be adding fuel when it's not needed. If there's any doubt replace it w/a PV more to the middle ground like a 65.
Getting back to timing, you saying the idle screws do nothing tells me the throttle blades are probably open too far in order to get it to idle w/the initial timing set where it is. Having the primaries open too far is enough to cause it to run partially on the transition circuit. Fixing the timing by adding to the initial (which will increase the idle speed) while keeping the mechanical from adding TOO much will allow the throttle blades to be closed back down enough that it will be idling primarily on the idle circuit- and then the idle screws will become responsive again.
For testing purposes you can basically ignore the mechanical advance just for now
. Add the initial timing, lower the curb idle screw setting, and see if that lets you get control w/the idle mixture screws and see if that improves the idle situation. You can even drive it that way as long as you are gentle on the throttle and don't romp on it. Keep the revs down and keep it from pinging by being gentle on it.
You can make a temporary timing tape
if you don't already have a timing tape on the damper or a dial back timing light. That'll let you see the advance beyond what the timing tab can show you.