Here's what I have, it's a 383 with a holley 750. It has stock GM heads, don't know what cam but it has a pretty decent lope to it when it's idling. The ignition is a street fire hei.

Here's the problem, when I drive it it accelerates pretty well. But when I try to hold it at a constant speed it runs poorly. I am not really sure how to describe it, it runs rough and sounds bad. I have messed with the timing and the idle mixture screws on the carb and can't do anything but make it run worse. I am not an engine guy, but I am trying. Anyway I would appreciate some opinions. Another thing I have a question about is spark plugs, how hot and what gap.

I know this combination will run because I had it running pretty well a couple of weeks ago. My brother (who is my engine guy) and I tried to make it run better and made it worse. Then he went home, bastard.... Problem is he doesn't really remember where everything was at when he started messing with it.

I tell you what, I had this and only by dumb luck did I figure out what happend.
Same issues, went through a couple of carbs, timing and everything I could think of.

It was the FUEL FILTER... It had gotten twisted and bunched up on itself and caused the same problem. I was so pissed that something so small created such a large problem... It would pull hard off the line and through 2nd gear but would hesitate in top gear.

Not sure this could even be a chance in hell, but worth the thought....

Is this a second hand built by someone carb or a new carb? What is your total ting when does it come in and whats your initial timing?

The quickest way to check if it's a timing issue is to disconnect and plug the vac advance can and take it for a test drive. What you've described is usually to much timing or a lean carb condition.

Initial timing 11 to 13 and total is 23.

I am pretty sure it isn't a lean carb issue. If I dissconnect the vac advance and take it for a ride how will I know if it is a timing issue or carb? You'll have to excuse me if that's a dumb question but I'm just learning here.

23 seems a little low to me, but I am no engine guy. I'm sure someone else will speak up shortly.

Initial timing 11 to 13 and total is 23.

I am pretty sure it isn't a lean carb issue. If I dissconnect the vac advance and take it for a ride how will I know if it is a timing issue or carb? You'll have to excuse me if that's a dumb question but I'm just learning here.

If you have only 23* total timing - there is your problem. You should have around 34 - 36 total. How are you determining total timing?

Disconnecting the vac advance will let you know if you have too much timing which causes the engine to surge at light load / cruising speed. That doesn't seem to be your issue at this point.

Check the carb jets on the front side, they should be somewhere near a .072 which should be in the ball park and not cause surging. If someone has put smaller ones in, change them out.

Post back up with progress and we'll see if we can work this out.

Can you explain how to set the timing at 34 degrees? Maybe I am doing something wrong there.

I am wondering also, could there be a problem with the vac advance on my distributer causing this? That distributer has had a close call with a fire on that side.

You need to set total first before anything else then tune the carb,
Dissconnect the vac advance and with an ADVANCE DIAL timing light set the dial on 36-38 since you have stock GM heads then rev the motor until you reach maximum advance it may be at 2,500 or 4,500 or anywhere inbetween. find that rpm then advance the distributor until the timing mark is on "0" with the dial on 36-38 on the gun.

How do I know when the motor is at maximum advance?

How do I know when the motor is at maximum advance?


You keep reving until it stopps advancing looking at the timing mark with the light

Alright, I'll see what I can do with it with the knowledge you guys have given me. I'll post back after I see where it gets me, probably won't be till Sunday that I can work on it. Thanks to all for the advice so far!

Have you checked you fuel level on the carb. If all of the other stuff you do doesnt work. You have a holley carb the level should be just where you can see it in the glass. to lower will also cause this. Adjust your timing, then adjust the fuel level then adjust the mixture.

Well, still no luck! Had it running really good Sunday, took it a couple miles, filled it up with gas, left the gas station, still running good, then a couple miles later it died. After I got it started again it started running poorly again, especially trying to hold it at a steady speed like before. So yesterday I took it to my brothers (he is an college automotive instructor) and he played around with it a little bit and had similar results, once it got warm it didn't want to run. So he and the other guys at the school are looking at it now. So far all I have gotten was bad news, low compression on #2.