Hope someone here can help. I'm running a stock 850 Holley on my '68 & it runs great. I picked up a very slightly used stock 950hp to try. Here is the problem: I rejetted the 950 to #83 primary & 84 secondary with a #6 powervalve in front & rear ( this jetting is comparable to my 850) After firing it up at the track the 950 idled great, but when you give it throttle it has a terrible miss. (2000 rpm's & up) Sounded like a 2 step. Incidently, we checked power valves & they are operating correctly. Where do i look from here????o No: Randy
holley Hello Randy , DId you check the Front squirter size is it the same ? i would go alittle bigger in the back jetting just my opinon..also i would go with a 4.5 powervalve depending on vacuum at idle..Goodluck :TU:
phone holley Hi Randy,I would phone holley or check holley book for ALL THE SPEC's put it back to stock spec's and if you don't know the history maybe put a kit in it at the same time.Do you know how to choose the right size power valve?Check vacuum in gear at a idle and go down 1.5 to 2 power valve sizes. Do you have the carb # I might be able to give you some info.Chris
Randy, in my 950 HP, I'm running 84's up front and 90's out back. I have a 4.5 power valve. I have about 15 lbs. of vacuum at idle. You may want to check the high idle bleed screws on the top and make sure the aren't clogged.
950HP This 950 has less than 100 miles on it. Stock jetting was 78on all four corners with # 6 powervalve front & back & 32 squirters. I jetted it close to my 850 as a starting point. When i tried this carb I upped the squirters to 42, Float levels are correct as well. It looks the majority here may think the problem lie with sizing of the power valves. I will measure vacuum at idle to see where i'm at. Phil, are you running a pv. in the rear? also, i'll check the air bleeds to make sure they are clean. This miss happens when throttle is opened up with car in neutral. It was bad enough that i didn't drive it in the pits. Thanks guys for a starting point for troubleshooting!! I'll keep you posted. Any more suggestions, i'm open!! :beer Randy
I'm not sure about your setup, but when my holley started acting up it would put too much gas in... it would run great at WOT but at part throttle and idle it would miss bad. From all the extra gas. Have you pulled your plugs to see what they look like??:TU: I had a 850DP... took it off for a 750 Qjet till I can rebuild it.
Holley HP Mine picked up 32 horsepower when we square jetted it at 90, blocked off the front and rear power valves and put a 2 inch spacer under it. Just my .02.
spacer Hi Carl,you probably picked up most of that power from the spacer and the better carb? The reason for the bigger jet size is to compensate for blocking off the power valve. This is taken right out of the Holley book; POWER VALVE PLUGS- A Holley power-valve plug, part# 26-36, shuts off fuel flow through the enrichment circuit. Plugging the primary power valve circuit is rarely necessary,and often creates unsolvable mixture problems. Without enrichment fuel, it is necessary to increase main jetting from 5-10 Holley numbers to regain adequate full-throttle performance. The increased main-jet flow at light- and part- throttle produces an extremely rich mixture, plug fouling and terrible gas mileage. Road race and street driven vehicles (that need excellent part throttle response) can not be jetted correctly with the power valve removed. An engine set up for drag racing does not need out standing part throttle response, but fouled plugs can still be a serious problem when the power valve is eliminated. Model 4150 Holley carbs sometimes have a power valve installed in the secondary metering block. Installation of a power valve plug in the secondary metering block, along with appropriate secondary main jet enrichment, is an acceptable modification for racing applications and will not significantly affect part-throttle operation. This modification can simplify secondary jetting on a race car; it is questionable value on a street driven vehicle. ANOTHER QUOTE FROM HOLLEY BOOK: Selecting the correct power valve can only be accomplished with a quality nonedamped vacuum guage.( This is for race engines) POWER VALVE SELECTION FOR RACE ENGINES equiped with high over lap cams is a different process. These vehicles often idle at speeds high enough to draw fuel from main metering system and develope manifold vacuum levels of 10-inches of mercury or less. This low vacuum at idle can open the power valve, resulting in a rich mixture, carbon fouled plugs, and poor throttle response. Observe manifold vacuum at idle (in gear for automatics) and select a power valve that opens about 2-in(hg) below this minimal level. I hope this answers some of your questions Randy. Your 850 is a different carb than the 950 HP, what works on one won't necessarily work on the other. I've been using Holley carbs for 15 years on my engines and engines I have built for other people and have learned not to try and re-engineer the Holley carb. They have come a long ways with there HP series carbs. .Chris
Thanks Everyone! I will start with the basics as you guys suggested & i'll let you know what i come up with. Randy
Thanks, Chris, for all the information. Information is always very valuable and I have gotten a whole heap of it here. I was just relating what happened with my carb. My engine is a race only engine. That is why I didn't make any recommendations. Just what worked on my engine.
Hey all, One time i had a miss like that with my 4150 holley... turned out to be a piece of gasket got stuck in one of the primary jets..
another issue I removed my tranny for a converter swap, found out my tranny case is cracked 180 degrees. So, that's my biggest problem! will keep you posted! Randy
CRACKED TRANNY NOW Grant, the crack runs from the top of bell housing around past the cooler lines on the bottom. By the amount of of dirt in the crack i speculated that it has been there awhile. Rossler transmissions said the crack came from an improper pinion angle. Knowing that the pinion was off ,I put 35 passes on it last year before i corrected it. Live & learn. :Smarty: Randy (wow Jeff, mine doesn't look that!!!) How did that one happen?
What your not seeing is the other half of the trans, with all the mounting ears broken off and the tail housing that was smashed. Lets just say that I wasn't having a "Smart Moment" when we put in the trans crossmember. (455/400 in a 84 Cutlass) I leaned the hard way to double check things and Deninatly to NEVER take short cuts ou: :gt:
Madcat 455- Hey, a "Smart Moment"? I've had SEVERAL with my tranny(s) also!! #1 reason why I now have a JW bell housing! Oh well, It looks much cooler, and alot stronger! I just wish they'd remake the WHOLE CASE over as thick as the bell housing! OUTRAGEOUS- Got an extra case lying around, you can just swap over the internals?? Only takes about a hour for a tranny guy, just need to reshim for end-play in different case.o No: :beer
