[1972BlueC20]

Ok so I've been having ongoing issues getting my truck running just right since I got a new engine installed. 350 / 330 HP Crate Part # 19210008.

The engine came with a Holley Street Avenger 670 CFM vacuum secondary, electric choke carb. The mechanic who did my engine install couldn't get it running right with the Holley so I got frustrated and had him put my old Edelbrock # 1406 on it so I could drive the truck.

Everything was ok with the Edelbrock at first, but shortly after getting the truck It developed a hesitation at cruise and from a dead stop. I had some ideas of things to try to remedy the problem but since I still had the brand new Holley sitting in my garage, I decided to give it a shot myself with the Holley before changing out the accelerator pump ect on the Edelbrock.

I'm having the following issues with the Holley :

Major hesitation when going from cruise to WOT (like a cut out almost chokes and dies)
Intermittent hesitation from dead stop
truck is dieseling sometimes

I've already done the following :

Verified proper float fuel levels. Front was correct, had to lower rear bowl a little as per Holley instructions.

Fuel Pressure is currently @ 5.5 PSI, I'm running a Holley fuel pressure regulator. Have tried numerous pressure settings within the exceptable range, none cure the hesitation.

Adjusted the accelerator pump, getting a good healthy squirt of fuel and there is no play in the accelerator pump arm, has proper .015 clearance.

Moved the stock accelerator pump camshaft to the # 2 position, no improvement...might of even got a little worse.

Choke is opening all the way once warm.

No vacuum leaks

Adjusted idle mixture screws while using a vacuum gauge, getting 20-21 reading on vacuum gauge in park, getting around 15 in drive.

Purchased the spring set for the vacuum secondary system. Tried all the springs from lightest to heaviest, none cure the problem.....just caused the secondaries to open at different times.

Pulled one plug on each side of engine to see if I had a obvious lean or rich condition. Below are pics, plug with a little brown was from drivers side, other plug is from passenger side.

Timing is 12 BTDC at idle, running with vac advance hooked up to timed / ported connection.


Here are my two suspicions of what could be going on, most likely one or the other probably not both :

1) carb is going too lean upon WOT and I need a bigger squirter
2) vac advance isn't working properly

Also I think the dieseling is being caused by my idle being too high. Only does it sometimes, had to increase my idle in drive because it was barely staying running at stop lights at first but then in park the idle seemed too high. Not sure of exact RPM because I don't have a tach.

If neither of these ideas fix the problem, then I'm going to pull all my hair out.
Haven't been able to get this damn truck running right since I got the new engine. It drives great when just cruising around normally, it even drives great when hauling butt except for when it hesitates during the transition from cruise to WOT. If I can just get the hesitation worked out I will be happy and quit bugging you guys for help LOL

I'm planning on getting an air / fuel mixture gauge and installing a wideband o2 eventually so I know exactly whats going on with my mixtures. However I can't do that for at least a few weeks or so.

Please let me know if you guys have any ideas or suggestions!