any ideas?
 

ok people.... pulled the carb apart today....lmk if this sounds right?. its a holley 750 dbl pump carb with 71H jets in the front w/PV installed and in the rear it has 73 jets w/extenders and with PV block off installed. now the motor is a mild 383 sbc w/alum heads and around 475hp that runs mid to high 10.70's in the heat and low 10.60's in the colder air with out making any changes to the car. now the car has a PG tranny w/5000 stall with 4.56 gears in a ford 9" and weights 2700 pounds with me in it :wink: my 60' time i feel should be in the upper 1.40s but cant get below 1.52 and not consistent :?

i got the 406 ready to go in the car but i want to find out why this motor isnt running lower in the 60's times first.... cause i know it should be.... :shock:

I assume you've played with the starting line chip to try hitting the converter harder, some where around 4200/4400 on the brake. I think you're right it should go in the 1.40's. Do you have a set of 4.86 gears? also you can back the cam down to 100/102 installed for more torque on the bottom end. My friend Jimmy Smith does this with his 3100 lb Camero with 358" engine and runs 1.47/1.49 60' times, but he also has a 5500 stall converter.

Just a guess

Zip.

i tried hitting the converter harder from 3500 up to 5k. it doesnt go below 1.52. 60' footers

my jets dont seem to be over sized but then again... they are just a set of stock aluminum chevy heads off an 85 corvette...? i wonder if it is to much fuel and needs to clear out and thats why it seems to make it up on the big end of the track and in cold weather?

i really want to figure this out before i switch to my new motor.... this lil ass vega should be running in the mid to upper 1.40's sixty foot times. if its not motor related and if its something else... i can change it all while i have the motor out :wink:

it ran 1.58 to 1.59's before i put all the fiberglass and replaced all the glass with lexan... plus switched 4000 to a 5000 converter! now i lost almost 400 pounds and went up 1k on stall and only drop down from 1.58's to 1.52's..... something isnt right :shock:

What size tire? How much tire pressure? Have you video recorded the rear tires as it leaves at the starting line?

31x14x15 @ i tried 8 up to 10 pounds. it doesnt seem like its spinning at all

Go up on the jetting, that looks a bit lean for a 750. Go up until the MPH drops off, then back to where the MPH was best. It should end up close to around 72-74 in front with the PV and 79-81 in back.

you really think it could be lean.....hmmm?

Yes.

http://i287.photobucket.com/albums/l...arbTrophy2.jpg

should i go up one set at a time or jump up to like 73 frt/78 rear and see what happens :wink:

What compression are you running :?: Camshaft lift and duration :?:

You can try it a jet size at a time if you like, your MPH will tell you how much power you are making and where it wants to be for jetting.

ok.... jegs had a full jet kit(69-99) on sale for $40.... and it just got here. :) im gonna go up two jet sizes in the front and three sizes in the rear and get the carb back together and bolted back on. im gonna start there and see what happens... i got all my time slips to compare it too :)

another question.... if it is running lean... could that be why the car runs a little hot and the temp rises really quickly from a cold motor?

Put those jets in a cup with clean gas and shake them around.I've seen sum pretty dirty new jets.Bill.

thanks bro :wink:

you hit the nail on the head :wink: im at 74f and 78r now and 60'footers dropped to 1.51 with a 1 and my et dropped from 7.0's to 6.90 and my mph went from 93/94 to 99.80's.

then my motor blew up... but you can only spin a stock bottom end motor to 7k for so long... 3yrs was it.... but got more then my monies worth out of that lil budget build 383 motor ... now on to the 406 to finish the season :)

here's a stupid question for the owner of the carb at hand
 

if your running a plugged pv in front with a heaver jet setting and a pv in back with a leaner setting,( i'm a fan of ) because fuel runs down hill persay! Did you rework your air bleeds to compensate for the fuel curve change in the holley 750 dbl pump just courious????? joeg 8)

didnt touch the air bleeds. im running a pv in the front only.... never tried one in just the rear..... ?

what is you vac reading in gear ? for proper pv settings also if you have adj air bleeds you should be able to run pv's in both blocks at that point you can square the carb to achive a realy good tune and fuel curve by squaring the carb that way your idle gets richer to get your idle a little leaner just change the idle air bleeds to a larger bleed dia. good luck joeg 8)

I would not use a power valve in the rear for a drag carb.Hard accelaration may let the power valve ports suck air making the jet extensions just about useless.Bill.

You should buy a bigger fuel pump! That can handle the demand of a high horse power application because it's about volume not pressure ! ( In saying that!) under a hard accleration with a good fuel pump that fills the demands of the bowls trying to empty out, that should never happen due to the fact that the bowls are at negitive pressure under acceleration the in coming fuel should fill bowls faster with the right fuel volume and pressure with a good high flow regulator with a properly set float adjustment and high flow needle and seats! There for the pv holes and and jet extensions should stay completely covered all the time good luck joe g 8)

Look at a metering block with a power valve.The power valve will be the first thing to get air when the fuel is forced to the rear.If thats not the case everyone could quit wasting money on notched floats&extensions.Just my opinion.Bill.

in the 60's before jet extension and notched floats what did the holley carb guru's do then ? holley does make proformance carbs don't they when you get it out of the box, do they come with jet extension and notched floats? I think the reserch and devolpment that they do weigh's heavy on what they sell the public, (maybe) just my thought on this situation joe g :)

Holley's ultra carbs come with a notched float instaled in the rear and extensions in the box.The power valve feeds to the main well are lowered to help keep them in the fuel.So just maybe even the big names can learn from us racers.For drag use remove the rear power valve,install the extensions and go up 6 to 8 jet sizes.The aluminum ultra is one of the best race carbs you will find and very adjustable.Bill.

Y'kno, for years, Holley's line of double Pumpers and then the Dominator series were the "Go To" when racing with just about any engine . . And, over that period of time, many racers learned to "Tune" Holley's by hook and by crook . .

Thus . . The only thing worse than a used Holley, is two used Holleys . .

Last year, I was introduced to a "New" Carb. The Pro Systems SV-1 . . We bolted one on a 496 BBC and ran it . . no dicking with it, nada, outa the box. 96 pills "square". It was "Slightly rich" but no blubber or smoggy plugs, beautiful tan insulators, one ring of heat on the plug thread . . Great, and a "Happy Motor" . . .

Had a problem with H2O in the oil, put in a 468 BBC with Dart 355 heads, never touced the carb, just bolted it on and went . .

Back to the 496 with the Dart heads on it, again, just bolt it on and run it . . Plugs look great, 1125° EGT, and now, we're running a 582, same heads, and still haven't done anything to the carb but adjust the idle air screws. same jets, same everything, just like it came out of the box . .

9.38's at 149-150 in 8500' corrected air, 2800# Iron 67 Camaro . . not to mention we've raced at 4800', 5000' and 6000' MSL and, again, never touched it . . And the motor's still "Happy" . .

It's a good piece of hardware that literally "self compensates" by working to the amount of air going through it . . .

Roadkill,I looked at that carb when I first heard of them.Looked trick but scared me.You are the only one I've heard give first hand info about one.Sounds like it did a good job for you on several motors.Bill.

Do not ever run a PV in the rear of a drag carb, there is absolutely no reason to run one there and plenty not to. A faster car can uncover the PVCR's and lean the mixture. On a trans brake equipped engine I don't run one in the front either, if the idle and transition metering are correct you really don't need it there either.

And then there are pretty carbs...

http://i287.photobucket.com/albums/l...2300LRCFX2.jpg

http://i287.photobucket.com/albums/l...Hybrid1050.jpg

http://i287.photobucket.com/albums/l...LRC145x175.jpg

http://i287.photobucket.com/albums/l...arbTrophy2.jpg