Ok 90% chance this isn't a carb problem but I figure I'd get the best responces here... I fired up my new motor and brought it up to 2500RPM for the break-in and everythings perfect and sounds healthy. After the break-in I shut it down and checked all the plugs they're in the "lil' too rich" color but definately not fouled or anything. Now I fire the motor back up and try to bring the idle down so I can check the timing with a light ...heres where the problems start... When you try to bring the idle down (trans in park) to like 1100RPM it starts idling really crappy. It sounds like a half-dead boat motor and will barely idle. Also if you put it in gear (with it idling at any RPM, not just low RPMs) the car stalls out.

My first guess is that the timing is too retarded? I have an MSD Pro-Billet and the way its setup now I should be getting full advance by 2500RPM. I hit it with the light while it was idling at about 2100RPM and had like 20* of timing. I cant give ya any lower RPM times cause the car barely runs... Another thing is my vacuum advance canister is like half an inch away from smacking into the intake? Maybe its in wrong?

Any other suggestions on what to look for? I have a Holley 4150 750 and its *really* old but I've rebuilt it and it looks solid inside. Cam is 238/246 @ 050, .480/.495 lift, 112lsa, and ignition is MSD Pro-Billet with 6AL box

In short form: motor sounds/runs great above 2000RPM, runs/sounds like a dead boat motor below that and dies when put in gear at any RPM.

Any ideas on what to look for tomorrow would be great.
Thanks,
Chris

 

go around the carb and make sure you got all the vacuum lines hooked up, there is one under the front bowl of the carb by the accelerator pump body that is very easy to miss. you may have to pull the dist and move it back one or two teeth just so you can turn it some more to set the timming. try advancing the timming manually while slowing the motor down at the same time, this should allow you to get the idle right and then set the timming.

 

After you do what redbird said I would set your timing at about 38 degrees, your motor should really like that cause I know mine does.

 

Well, I messed around with it today and think it is a carb problem. I fired it up without changing anything and let it run for like a minute. It was so rich my eyes were watering. So I turn it off and turn the idle mixture screws all the way in then fire it back up and the car will still start/run. I also noticed a very slight amount of fuel leaking out of one of the mixture screws.

So there must be some sort of fuel leakage inside the carb? The car should NOT run with the mixture screws all the way in, correct? I'm gonna replace the powervalve and go over everything inside the carb again.... I hope its something stupid and this carb isn't just junk.

 

Pull the distributor and put it back in with the rotor turned one gear tooth clockwise (the oil pump shaft won't line up anymore, but just bump the starter to get the distributor to drop - AFTER you've done the one-tooth thing). This will allow the distributor housing to also rotate clockwise so you can turn it counter clockwise to get the proper timing advance. When you set the timing for total mechanical advance, the vacuum advance must be disconnected (also make sure it's all in by reving the engine beyond 2500).

Next is float level. You didn't say anything about that, so I'll say it for completeness sake - Make sure the floats are adjusted properly.

What type of carb is this exactly, double-pumper, or vacuum secondary? Probably doesn't make any difference, but the secondary throttle blade stop may not be set right, either.

 

the powervalve may be the key to that one. if you have low vacuum at idle because of the cam then you have to get a powervalve that stays closed with the vacuum that you have at idle. you have to find a balance between that and when you want power enrichment when you step on it, all in the good fun of tuning a carb, it took me a week and three powervalves to get it the last time I used a holley on something.

 

The carb is a very old 4150 Holley 750cfm double pumper that I rebuilt. I've rebuilt a few carbs before so I'm pretty fimilar with the inner-workings and everything looked good inside... My floats are fine they're just below the sight plugs and I've got 7psi of fuel pressure. As for the PV its a 6.5". I had a vacuum guage hooked up and has like 14-16" of vacuum at like 1800RPM (the lowest RPM I can get it to idle on its own)

If you let the motor run at like 2500+RPM the plugs stay clean but once you drop it down they go black.

 

I changed the powervalve and took the mixture screws out and ran carb cleaner through them. Still the same

 

An idea popped into my head that my carb is just completely bypassing the idle circuit (thus why it runs with the mixture screws all the way in) because my primary throttle blades are open too far and to fix this problem you can open up the secondary blades or drill a small hole in the primary ones? This is the first mechanical secondary carb I've run so I'm not completely fimilar with it. How do you set the "secondardy throttle blade stop" and how far are you supposed to open them?

Although I still havent been able to get a timing light on it, I turned the distributor until it hit the intake just to see how it would run.... Tried starting it and it would barely turn over. I have a high torque mini-starter so I'm guessing timing is not my problem.

Thanks,
Chris

 

Get the ignition right before you try to "fix" carb problems - 1st rule of carb tuning. Get a timing light on it and verify.

 

Well, I cant get it to idle below 2000RPM so I cant see what the timing is at down in "idle territory"..... Its like 19-22* @ 2000RPM this was before I stepped the timing up even farther so I'm pretty sure its getting enough timing at idle RPMs.... yet it still doesn't. If I advance it any farther I can't even start it.

 

I'm curious, whatever happened with this? It is exactly the problem I am having now. How did you fix it?:hail:

 

Timing mark was off so what I thought was the intial timing was actually like 10* more retarded... That explained the crappy idle After I got the timing sorted out I still had the problem where it would stall in gear... That was because the idle mixture was too lean.