I was running a 650 edelbrock on my engine and my car ran 12.6 in the 1/4 mile but I bogged off the line and couldn't spin the tires. I Put a Holley 750 DP with a Proform main body on it that should flow well over 800cfm, now the problem is that I spin the tires off the start and don't bog but now I have no high RPM power and the car only runs 13.1 with the Holley. This really boggles my mind because I thought the larger carb would give me the exact opposite results. My first runs with the 750 were with 72/82 jets and I ran 13.5, then I put in 76/86 jets and it ran 13.1. All my 60' times suck and are in the 2.0-2.1 range. Should I try even bigger jets? It feels like I lost all the high end power when I switched carbs. Also my mph dropped from 112 mph with the 650 to 108 with the 750.
Please give me some advice on what I should try.
Thanks.

 

#1: Float levels (basic, but it needs to be right).

#2: Fuel pressure - monitor for the entire run and make sure it stays at least above 4 psi.

 

What is the rest of you combo?

I can't comment without knowing, but have alot of experience with holleys and would like to help.


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Maybe your timing is advanced too much and that made you lose some top end. Just a thought.

 

Fuel pressure doesn't drop below 4 psi, timing is 38 degrees total. engine is a 350 with trickflow heads, performer rpm intake, LT's, 9.6:1 comp, extreme energy 236/242 roller cam, roller rockers, etc. I just rebuilt the Holley DP and found nothing wrong with it, I am going to try smaller jetting and drop the timing to 36 total and see how it runs. Right now it just runs horrible above 2500 rpm but there isn't any bog when I gun it, this is what confuses me the most.

 

Typically bigger carbs take bigger jets. Tune by your mph not ET, keep going up in jet sizes until mph falls back off, then go back 2 sizes.

I had a problem and lost .3 when I had to install a small fuel pump to get me by, it was down to 3psi at WOT. Try to set pressure so it stays at least 7psi to 8.5 psi while going down the track-especially at the big end where inadequate flow will show it's ugly teeth.

Get your jetting close, then start messing with timing and once your where you need to be with the timing go back and fine tune jetting for the last time and call it a day.

 

I rebuilt the carb, set it back to stock accelerator pumps, stock size air bleeds, 73/81 jets and it still doesn't run right or as powerful as it did with the edelbrock. I will look into my timing curve but my engine usually liked 39 degrees total timing with the curve kicking in full timing at 2500 rpm. I'm kinda stumped with this Holley.

 

I am stumped too.

It sounds like it is running too rich.

The reason that I believe this is it is ok out the hole but will not pull and does not stumble.

Could a power valve be blown or is something else not allowing the proper misture needed at higher RPMs

Are all the passage ways clean?

Dont know what else to suggest.