my 350 rocket is stock except the cam msd system and carb and it runs fine until I give it full throttle from a stop or from around 30 mph I know my exhaust choke block off has a leak can that cause it I drove it at w.o.t on the interstate before the leak started now at w.o.t it back fires and tries to die
carb is a holley 4150 600 cfm d.p

 

Sticky valve?

 

[QUOTE=farmer52;963736]Sticky valve?[/QUOTEi

the carb is a bit to big and I had it set to lean I cured the rolling w.o.t I'm still trying to figure out the off idle stumble and backfire

 

All the stuff I have read about double pumpers said you need a high stall or manual transmission since the secondaries open immediately and the engine can't use the available air/fuel at low RPM.

 

its 'supposed' to be a vacuum 2nd according to summit racing
the stock worn out 500 cfm 2 barrel Rochester would boil the hides the 600 4 barrel wont it stumbles

 

You can look at the carb to find out what it is. If it has two accelerator pumps, it is a double pumper.

 

it got 1 so its just a dual feed I got most of the hesitation fixed carb was to lean itll chirp the tires now but it still gets smoked by the ols 2 barrel it still pops out the carb when I hit it to full throttle when cold but the exhaust choke block off is leaking air so I can get it tuned in

 

I was going by your first post where you said it was a double pumper:

 

my mistake its a dual feed vac secondary

 

Back in the 80s I had a Holley 600 and I had to install a secondary vacuum diaphragm spring kit to tailor the opening rate so it would launch properly.

 

If it ran good with the 2bbl and not so good with the 4bbl....why not put the 2bbl back on?

 

the 2barrel was dumping gas and the body was warped and the local parts store couldn't get a 2 barrel for 2 weeks and it was 50$ more then the 289 I spent on the 4 barrel I'm changine to a 4 barrel intake in January when I sprayed either at the carb base the only leak was the exhaust choke so its causing it to run lean

 

What manifold is on there now?

 

stock 2 barrel with a carb adaptor

 

That is not going to work well. I bet its flooding and that's contributing to your backfire.

 

Gettin' on er' and puttin' er' up to 6500 RPMs isn't going to help it much either haha!!
I'd think about gettin' on something else if you have that much energy, maybe somethin' in the back seat. Jus' sayin'
I've wipped springs out of back seats back in the day, pffft while flyin'
Put-er-ther
Eric

 

got it fixed timing was retarded to far back

 

haha just for the record I wasn't driving my girl was needless to say my tach is 600-750 high and its sticky

 

Careful turning a stock SBO that high. Thats ~5800 rpms. That's still high.

 

So you have a Holley 4bbl going into a carb adapter into a 2bbl manifold?

 

yea not the best way to go I know but the car was on the side of the road and it was 2 weeks before the parts store could get a 2 barrel I'm goin to a 4 barrel intake longtube headers and dual 2.5 in exhaust in december

 

That should wake your 350 up some. Your neighbours will really hear you after that.
Have you got the cam/chain sorted out?

 

I'm not sure its running ok though