The car was running good for about a week or so after getting back on the road after some wiring issues. I was cruising to work on the highway at about 50mph running good when I heard a slight pop/backfire and that was it. It started running like crap. Wouldn't idle and was backfiring a bit. This very same thing happened before after revving the engine way up passing someone and downshifting. I thought I floated a valve back then. I had a valve adjustment done and everything gone through (carb rebuilt and cleaned, ignition checked out etc). Was great after that.

Now, I'm back to troubles. So, I pulled the carb apart and cleaned it all out, replaced the powervalve and gaskets and bolted it back together. I also cleaned all of the plugs as well as the terminals inside the dizzie cap. I still couldn't get it to run right. It seemed like the carb wasn't choking right.

I checked the lead on the electric choke and sure enough, no voltage. THe fuse blew. I replaced the fuse and viola. However...

now the idle is FLYING and I can't get it down. The idle screw is out. I've tried to turn the idle mixture screws in and while it does slow the idle a bit, it starts to give me a lean "pop".

It almost seems like the dizzie is way advanced, but if I turn it either way too much to drop the idle, it backfires and sputters badly on throttle.

Question 1: turning the dizzie which way advances the spark, clock or counter clockwise?

Question 2: what would keep the idle SO fast and prevent it from being reduced? nothning is impeding the linkage and I've not found a vac leak anywhere.

Question 3: i had a Holley 650 double pumper that was tuned and flowed to about 690cfm on it originally but the plugs always seemed rich. It was suggested that I drop to a vac secondary 650 so I did but the car never seemed to have as much umph. How do I know if the secondaries are engaging? I'm thinking about going back to the bigger carb. Thoughts?

Question 4: with the 650 vac secondary carb, what would you recommend for main jet and squirter size? It has 79's for jets and the stock squirter.

This is an 11-11.5:1 roller destroked 350 with a 327 crank...if that helps

Thanks tons guys!!

#1 - turning the distributor counter clockwise advances the timing.

#2 - there is something blocking the throttle blades from returning to normal position - either in the bore (gasket blocking the blade) or with the choke cam. Normally, you would step on the gas to release the choke cam, but it may be stuck.

#3. It's fouling plugs because it's too rich at idle. ANY size carb can do that, it just needs to be tuned. 650 is probably a good size carb for your setup. Get a secondary spring kit for the carb, swap the spring and see what happens. You've really gotta make a change and then drive it (one change at a time) to see the impact.

I got the idle down. I don't know what it was, but I fiddled more with it and i was able to get the idle down to where it needs to be.

I thought that counterclockwise advanced it..thanks

It was suggested to me once by a guy that had lots of cars from drag cars to hotrods that black smoke or fouled plugs does NOT always mean too rich. He suggested that it can be caused by a lean misfire. Too little gas in the cylinder keeping the ignition from firing completely gives you a partial burn leaving residue. Anyone hear of this? Sound plausible? When I had the other carb and wsa spewing lots of black smoke (early in the build), i of course said "whoa, we need to drop the jets." He said the opposite and upped them...no more black smoke.

Not sure of that jetting theory. At idle, your jets should have no effect - only the idle circuit should be working on a properly tuned carb. See www.holley.com for some good info on the way the carbs are supposed to work.

If you completely close the idle screws, I think the car should die. If not, it's pulling gas from somewhere. Maybe the throttle blades are not set properly, etc.

Could be a leak in the carb somewhere, etc. Double check all the screws (underside and topside) for tightness. Then I would start by returning the carb to stock specifications, then start the modifications from there.

Did you put a new power valve in since it backfired? Not all of the carbs have the newer backfire protection.

I'm pretty versed in Holley's since I've had to tear them apart so many times! Yes, theoretically, if the idle screws are bottomed out, the idle circuit should be starved and the car die.

I replaced the powervalve after the backfire. I unfortunately failed to take a vaccuum reading before installing the powervalve and have the wrong one in there now. I'm getting about 18in of vac at idle which means I should be using a PV rated about 8.5. All I had was a 6.5 to install. That can yield a lean spot on throttle since the PV isn't opening soon enough.