Specs for my motor in my sig. Ive heard people telling me that a 600 double pumper is too small for a 383, but Im not too concerned about that right now. My main concern is the fact that after idleing in my garage for 1-2 minutes (door open of course), it burns your eyes just to stand in there. Obviously ots running waaaay too rich, but is this a sign of a bad power valve? When we first cranked the motor over trying to get the timing right, it did slightly backfire through the carb.

This might also possibly be related. It seems that I have an intermintent miss (again, mainly at idle). Could this be from a bad power valve?

I took a vaccum reading from the back of the carb where the PCV hooks up. its reading about 15-16", which supprised the heck out of me with this cam. I figured it would be a little lower than that. But with it being a double pumper, and a manual trans car, does it matter if the motor is warm or not? I read on here that for VS carbs it needs to be warm.

about a 7.5" power valve should do the trick ya think?

 

The power valve only affects the main metering circuit. If it is rich at idle, it ain't the power valve; unless, of course, the main idle speed screw is holding the throttle blades open so far that the main circuit is drawing fuel.

Newer carbs have a check valve in the PV vacuum sense port to prevent blow-out in the case of backfire. They can fail, of course, like any other component. But, if the carb is at all close to being adjusted properly at idle, that shouldn't make any difference.

One effect of having too small a carb on an engine is upset of the air bleed ratios. Most likely, your idle air bleeds are being overwhelmed, leading to the rich condition. However, an intermittent miss leads one to suspect you have ignition issues that should be considered before monkeying with the carb.

 

well, I replaced the PV with a 6.5" one. And now it runs worse than before. Backfires through the exhaust, stumbles, doesnt want to idle below 1000rpms. I guess its in the carb tuning somewhere. I pulled all my spark plugs out so I can clean em tomorrow. All were pretty much black with the exception of 2. the #2 plug was almost brown, so Im thinkin thats where my skip is comin from. Theres almost no black, all brown and slightly white. And I believe on the #7 theres some black gunk, Possibly valve seal, I dont care at this point. Im just hopin with cleanin the plugs itll help it run better.

But what gets me is that the night before, with the same settings and with a bad power valve, it was runnin decent. RICH as hell, but it was ok. Pulled the PV out, and it was blown. Replaced it, and now it runs like crap.

 

check for vacuum leaks as well, sounds like you put the carb back together wrong if it's running worse with a new powervalve. although i'm a newbie at carbs too, so take it with a grain of salt.

 

#2 is probably the only one that's firing close to correctly.

Replace the plugs, and check the wires & cap for issues that could keep proper juice from getting to the plugs.