950 holley ultra hp carb jetting

[fryedaddy]

i bought a 850 double pumper new in 1985.i have run it on 3 fe engines over the years.it gave out on me last year,just wore out.i bought a 950 ultra hp off a guy.no choke,no pcv hookup.he had blocked the power valve off in the front and the back has jet extensions.he had 74 jets in the front with no power valve and 78s in the back no power valve with jet ex.i tried it and it sounded good at idle but when i took it for a ride it fell on its face.i put a power valve in it and tried jetting it up a few times.when i got it running good i had 88s in the front with a power valve and 96s in the back with jet extensions and no power valve.does this sound like overkill. i have a decent motor. its not stock but its not a monster.

[KMcCullah]

I like to run power valves on the street because they save a little gas if they're sized right. My race junk I don't use power valves on. Without a working power valve on the secondary side, I don't think your too out of line with the jetting. Did you size your power valve at about half of your vacuum at idle? That's a good place to start with.   Also.... with the stumble your describing, it sounds like you might be running out of accelerator shot before your venturi's start to work. Have you played with shooters and cams yet?

[fryedaddy]

i didnt stumble till wot,it ran ok just driving at half.yes i played with the squirters and tried diff.power valves.im just thinking i may have too big of jets.it runs and starts good

[fekbmax]

The 74's and 78's with 'no power valves'  sounded way under jetted to me, it was as if he left stock jet in and just blocked the power valves. I don't know anything about your combination but the 88's in the front with a power valve sounds pretty fat to me. Sounds like your in the ball park with the 96's and no power valve on the secondary side, maybe just a little fat there to.
So man things come into play though,  . mybe try just old school power tuning it .

[turbohunter]

fryedaddy I'm wondering about a couple things.
First, "wore out", why not rebuild the 850.
Second, off idle stumble would lead me to check transfer slot, accelerator pump, the pump linkage and squirters.
Third, "not stock but not a monster", would make me think the carbs to big ( maybe not, though I know nothing about your engine).
Just passing on thoughts.

[fryedaddy]

fryedaddy I'm wondering about a couple things.
First, "wore out", why not rebuild the 850.
Second, off idle stumble would lead me to check transfer slot, accelerator pump, the pump linkage and squirters.
Third, "not stock but not a monster", would make me think the carbs to big ( maybe not, though I know nothing about your engine).
Just passing on thoughts.

the 850 has been rebuilt a few times, im done with it.the stumble was at wide open,say riding along at 55 and kick it in it seemed like it was out of gas at wot. but it dont do it any more now that i jetted it up. i looked up the 950 carb it came with 92s square.that guy had it jetted down bad..engine is a 433fe,11to1,comp cam,msd,etc.

[turbohunter]

Ah ok misunderstood.

[manofmerc]

Last year I built myself a 950 .I had an extra quick fuel 950 main body and purchased whatever else I needed .For jetting I went by pro forms specs for the 950s they sell .I have 84 front 93 rear .No power valve in the back and a 4.5 in the front .I pulled the spark plugs and they look good .My engine is a 452 427 with 428 crank edelbrock heads 237@.050 cam this is a stret car only .I would run a power valve in the front and keep the rear blocked .If your engine isn't really big (390-428) maybe try 80-90 jets I have been jetting my 460 powered drag car recently it has a 1050 quickfuel 4150 series so far it has run the best with 88 93s 10.89 at 120 I really want to put the 950 on the drag car and see what that will do time will tell .Another thing look at your needle and seats if it has 110 stamped on it try a 120 you will have more fuel available for the bowls .The 950 seemed to be running out of gas until I put in a 120 needle and seat .When I went from a 750 to the 950 it was like waking the dead .Doug

[fryedaddy]

same here ,i had a 950 main body.i put quick fuel blocks on it and the larger bowls that hold 25% more fuel.my engine is a 433,my cam is 245 at .050,11 to 1,alot of head and intake work and porting.i dont know all the details.my uncle had the machine work done for me.he was showing me the reciept from the machine shop,pointing out some of the things they had done to my motor.i tried looking at the bottom line that showed the total cost and he wadded it up before i could see the cost and he said we wont worry about that.he passed away a few months later and i never got to see what all work went into my motor.its pretty stout for what it is. my uncle and cousin raced fe engines on round track for many years. maybe those 88s and 96s are pretty close after all?

[manofmerc]

Really the only way to tell if your jets are right is to go to the drag strip.This weekend I took my 460 comet to the track .88 front 93 in the back .I went from 93 to 91 it slowed from 10.86 to a 10.92 and from a 93 to 95 et was the same but mph picked up one 118-119 .Probably you are close on your jet sizes .I would like to take my 950 and test it back to back against the 1050 I have on my comet at the track .Somehow I think they would run really similar times .Good luck to you with yours!Doug