350 sb problem

Please help with my 1923 roadster engine problem. NEW: 290hp.350 sb, th350 trans.,2100 B&M converter, Pertronix Flame Thrower dist. and coil. 3 Rochester 2g's completely rebuilt, plus fuel pump, balancer, etc. Eng. will start but the advance is about 30 degrees, will not run with any less. Have reinstalled dist. dozens of times with no change unless to make it worse. Pulls about 12" of vacuum @ idle @ 1000 rpms. In gear, idle drops to 500 rpm and barely runs. Have adjusted idle mixtures with vacuum gauge to the highest indicated vacuum. It just won't run @ 12 to 14 degrees advanced with vacuum plugged. Total advance is around 50 degrees-not good. Have driven car and she runs nicely at speed, runs on middle carb only until 3000 rpm when the other two kick in. Have checked for vacuum leaks-none found. Have MSD 6 box installed but thinking of bypassing it since the Pertronix doesn't require it to see if it makes a difference. This engine just is not running correctly especially since everything is new. Maybe that's part of the problem, she just needs to run more. Any help is most appreciated since I'm obviously missing something. Thanks.

 

Not what you want to here but I would be checking the timing chain, it may be out of time! Gary

 

Are you sure about your TDC?

 

You need to verify your marks with a piston stop test.nothing else will do or matter much until you do.

Your Trans needs more vacuum at the modulator.
Correct the timing first.

Toss the light on the bench and set it by ear and vac gauge.

 

Everything reads good, except for the MSD 6. Why are you running it? Recheck your timing. Try readjusting your idle mixtures. I like in gear at idle, around 650-700 RPM's.

 

If you eliminate the MSD box and still have the problem, next step is to subsitiute a different distributor.

You state that this is a new 350/290 GM Performance engine. Did you change the camshaft? Which balancer/timing pointer combination did you use, were these from a running engine or spare parts from the garage?

If none of these suggestions solve your issue, PM me. I am at a GM Performance dealership. Before you open the engine up to check anything I will give you a Tech Assistance phone number at GM. They are there to assist customers in the rare instance of trouble with a new crate engine.

This being said, I'm still leaning toward a issue with the Petronix. I had one fail last summer. Starting the car it would act as if the timing was extremely advanced at times, hot or cold (like two days not run cold). Finally it quit while hot on delceleration and would only restart when shut off for a minute or two. Replaced with a Mallory distributor set to the same timing specs and no more cranking issues.

 

Does it run good/normal at 50 degrees? If yes, my guess is the timing mark is in the wrong spot.

 

This has been discussed before. I am very familiar with this crate engine. Read here:

http://www.jalopyjournal.com/forum/showthread.php?t=649643

Run it with the timing advanced and it will run fine. The timing marks are correct and your light is fine. It is a low compression engine with a lot of camshaft overlap. I am sure it runs great at high rpm as well.

Set the total at about 45-50 degrees and don't use the vacuum advance. Let us know how it runs. I personally know of dozens of these particular crate engines running fine for years like this.

If you look at my posts in that thread I linked to above, I have a link to the exact engine you have.

 

LISTEN TO BAD BANANA!!!!!!! These engines like a lot of advance.

Bad Banana is the maestro of these engines.

 

I have worked on a few of these and yes the want a lot of advance,I do use the vacuum advance.Compression ratio on these is in the 7.9 range.