hesitation during light throttle acceleration.....750 holley

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wyrmrider
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Re: hesitation during light throttle acceleration.....750 ho

Post by wyrmrider »

it should not be running on the primary jet
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Re: hesitation during light throttle acceleration.....750 ho

Post by Truckedup »

My guess based on some experience, poor fuel vaporization at low speeds causes a momentary lean out...In the "old' days this was common with unheated intake manifolds.....
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Re: hesitation during light throttle acceleration.....750 ho

Post by mbrooks »

As a test raise the floats a little see if that has any effect.
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Re: hesitation during light throttle acceleration.....750 ho

Post by F-BIRD'88 »

Be sure there are no manifold vacuum leaks before you blame the carb.
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Re: hesitation during light throttle acceleration.....750 ho

Post by Rick1999 »

GARY C wrote:
rewguy wrote:It has a single plane....No spacer, and as far as timing....The LS1 style engine seems to like from 28-32 degrees for the most part. It has currently 30 degrees from basically idle to redline. It also has currently 1 1/4 turns out on the idle mixture screws. It is a basically stock jetted/ stock air bleed/ holley 750 HP.
My guess is it's to lean for that ci and cam, if you have access to an 850 you can borrow my guess is the problem will go away...If you have the ability to richen the idle and transfer circuit then that should solve your problem, if not then send it to someone who can.

increasing the primary jet may confirm if it's lean...but that is really not the primary.
Putting a larger carb should not have any effect except for the idle may be set up slightly richer, The cfm of a carb doesn't really have anything to do with it, if the carb is larger it will draw less fuel through the same size metering orifice. It could help but just as easily make it worse, the problem is getting his carb properly calibrated for the engine it's on. HP style carbs come with removable air bleeds, go down .003" or so and see how it responds would be the first thing I would try, you'll have to readjust your mixture screws when you do this, 1 1/2 turns out is generally accepted as normal but I seem to have better luck when they end up between 3/4 to 1 turn out. Beyond that you have pump cams and squirter size to play with, those come with pink cams I like the orange or blue with an open plenum. You should not even be on the main circuit where you are having your problem so I wouldn't expect much from a jet change and if it does fine when you stab it hard the jetting is probably very close and finally never change just the primary jet that will give you more problems in every other area of the rpm range.
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Re: hesitation during light throttle acceleration.....750 ho

Post by GARY C »

Putting a larger carb should not have any effect except for the idle may be set up slightly richer,
Thats why I suggested it! If it fixes the problem then he knows where to start with his current carb.
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Re: hesitation during light throttle acceleration.....750 ho

Post by Rick1999 »

GARY C wrote:
Putting a larger carb should not have any effect except for the idle may be set up slightly richer,
Thats why I suggested it! If it fixes the problem then he knows where to start with his current carb.
I understand what you are saying but just because it's an 850 doesn't necessarily mean the idle is set up richer. Bone stock, yes it would be but you never know if it's been messed with by somebody else. His carb is an HP so it has removable air bleeds, easier to change than the whole carb (neither is very hard) but I think it would be better for him to figure it out with the carb he's going to be running rather than try and duplicate a carb that's not the same as what he has. There are many ways to do this stuff.
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Re: hesitation during light throttle acceleration.....750 ho

Post by GARY C »

Rick1999 wrote:
GARY C wrote:
Putting a larger carb should not have any effect except for the idle may be set up slightly richer,
Thats why I suggested it! If it fixes the problem then he knows where to start with his current carb.
I understand what you are saying but just because it's an 850 doesn't necessarily mean the idle is set up richer. Bone stock, yes it would be but you never know if it's been messed with by somebody else. His carb is an HP so it has removable air bleeds, easier to change than the whole carb (neither is very hard) but I think it would be better for him to figure it out with the carb he's going to be running rather than try and duplicate a carb that's not the same as what he has. There are many ways to do this stuff.
Yeah it would probably be best to measure the idle fuel jet first, I just find it easier to change carbs or for that matter the primary metering block to see if it addresses the problem as oppose to mortifying my entire carb before I even know whats wrong with it.
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Re: hesitation during light throttle acceleration.....750 ho

Post by JoePorting »

Could just be a clogged or restricted air bleed or emulsion hole problem. Quick fix is to take a can of carb cleaner with the tube installed, and hold the tube against all eight air bleed holes and give it a good three second blast of carb cleaner in each hole. If the emulsion holes are really clogged up, you'll actually be able to hear it open up as you are blasting away.
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Re: hesitation during light throttle acceleration.....750 ho

Post by F-BIRD'88 »

compressed air blast in the air bleeds works too. Keep your face back, during.. It will spray back.
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Re: hesitation during light throttle acceleration.....750 ho

Post by Rick1999 »

I wouldn't recommend blasting carb cleaner or compressed air into the air bleeds of an assembled carb. I've done it at the track when there was no other choice, but if an air bleed is clogged that trash has to go somewhere, usually into another orifice in the metering block. Take the bowls and blocks off the carb first.
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Re: hesitation during light throttle acceleration.....750 ho

Post by GARY C »

F-BIRD'88 wrote:compressed air blast in the air bleeds works too. Keep your face back, during.. It will spray back.
Thats how I test my carb cleaner, the one that burns your eyes and skin the most also cleans the best...Barryman B12 still holds the record!
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Re: hesitation during light throttle acceleration.....750 ho

Post by My427stang »

I haven't done one in a while, but I had a run of those HPs that the only way I got rid of that annoying hesitation was by replacing the metering block with one that had a low IFR

The low IFR, vice top of the block, isn't the cause, I think it's the main well emulsion design, but it's the easy way to spot a good earlier block. In each case, I just matched the jet, IFR and PVCR sizes and drove away amazed. Never had a HP750 come through but did it on a 1000 HP, a 950 and a couple of 670 Street Avengers.

Try everyone's advice, but if you just can't get there, find some moldy old 1850 work the block, and my guess it'll run great
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Re: hesitation during light throttle acceleration.....750 ho

Post by jmarkaudio »

Lowered idle feed will improve idle and off idle transition. Link to the mod below. With a 750 start at .033 restriction and a .070 idle bleed, adjust the bleed to suit.

http://racingfuelsystems.myfunforum.org ... ?f=25&t=18
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Re: hesitation during light throttle acceleration.....750 ho

Post by mbrooks »

I'm playing with a Ultra hp750 right now, similar engine but ford. I've found an iab of .073 works with a little spike prior to the mains coming on, .076 smoothed it out, anything smaller just exaggerated the spike. .076 is right on the edge of off idle too big, so either one should work. IFR of .031 made the cruise right around 13.5-14. This is with vacuum advance and single plane btw. I have a sheet from prosystems for a carb that spec'd .076 on the primaries and .073 on the secondaries, that will prob work. They spec'd .035 on the ifr but that is going to be a little fat in my case, I'm gonna go down from the .031 on the primaries and see what that does for cruise. Lowered idle feed btw.
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