355 sbc missing under load only! Help!

[Floydcw08]

355 sbc missing under load only. Hei distributor, holley 750 carb, edelbrock mechanical fuel pump. Motor will rev to 7,000 rpm with no problem while in nuetral, but as soon as im on the track under a load it starts missing badly. Timing is 36 degrees . Changed plug wires and plugs. Also changed fuel filter . Help!!

[kraftkar7x]

Have you tried changing coil on cap had same issue changed everything you did even changed dist never thought about cap then I put new cap on and it ran perfect

[Floydcw08]

I will give it a shot thanks!

[jsf74]

Had the Same problem here and same fix.

[powerslide]

Float crushed?

[riddle28]

fuel pump pushrod?

[mod 44]

Did you check the pick up on the distributer make sure it has no rust build up it is what happen to mine I took it apart and cleaned it the it went away

[shadowj38]

what kinda carb are you running? i had the same problem running a proform carb and found the rear float was made of a plastic and had a pin hole in it. i called proform and said they had been having problems with it. they sent me a new float free of charge and it fixed my problem.

[Floydcw08]

Im running a holley 750 carb. We put a brand new msd billet distributor and box on it. Also the fuel pump is putting out good pressure. Still same problem

[Lizardracing]

Plug gap to wide or faulty plug wires. Also try disconnecting the tach in case it's grounding out and change or remove the MSD RPM chip.

[Floydcw08]

Changed plug wires and took the chip out. Same result. The fuel pressure does drop considerably on the throttle though. Going to try and change the pump and see what that does. What plug gap is everyone running.

[speedbuggy]

I vote for plug gap, either too wide or too narrow.

[Floydcw08]

Checked the plug gaps today and they are .050 Any reccomendation on the gap they should be? Im thinking the .035 to .040 range

[setup479point2]

Fuel pump should not drop pressure under throttle. 12v .035 gap , 16v .045 gap or less .

[Lizardracing]

Are you using the HEI type coil when you changed the dist to a MSD with a MSD box? You didn't specify what type of MSD Dizzy you used.

X2 on the .35 plug gap.

[Lizardracing]

You can isolate the problem further by disconnecting the secondary on the carb. That's going to rule out something on the secondary side like float, power valve, air bleeds and such.

[Floydcw08]

Figured it out today. The carb had way too big of jets in it. It was loading itself up. Dropped the jets to the size they should be and it runs great. Also changed the plug gap to .035 car runs great. Thanks for all the help.