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I have just joined this site and kinda new to Drag Racing. I`ve been around my Dad who is all about D/Racing and he has helped me get to where im at now and I don't want to bother him cause I want to prove to him I can figure problems out on my own. I have a 3200 lb. 70 nova and it has a 383 with 220 cc heads, victor jr intake (ported to match heads) with a holly HP 750 carb. 302/296 adv. 270/263 @ .050 .600/.588 solid roller, 13.65-to 1 comp. with 1 3/4 headers, 5000 stall in a th350, 5.43 gear. now for the problem it has run a best et of 6.80 @ 100 mph. the car is busting out on the top end in all three gears. I keep putting larger jets but it still dose the same thing. I have 98`s in the front and 92`s in the rear. I run a holly blue pump with 7 psi @ the bowles. I have tried all I no to do and im in need of help. I know my dad could fix it if I ask him but I am wanting to do this on my own. thanks for any advice.

David
 

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Discussion Starter #2
sorry guys correction on the lift numbers. guess I got stuck in stupid. the lift is .700 in .688 ex on 106 centers
 

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TwistedTerror
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That is way to much jet for a 750, unless it is an alcohol carb? Also usually you jet the carb square or the rear higher. Very uncommon to jet the front higher. I had my old race gas dominator jetted 8 up in the back over the front. Well I put them on backwards one day on accident. It ran like shi* then I figured out what we did wrong.

My 383 has 200cc Pro1's on it, had .653/.608 lift after lash. And I ran 6.73 @ 102....that motor ran quicker with a 1050 dominator.

IN MY OPINION, you need a bigger carb. That 750 isn't cutting it, I don't think. Your base plate and venturi size of that 750 is only so large. You can't keep throwing jet at it...eventually it needs more cfm. If you could try a larger carb, leave it at factory jet size in the front. Block the rear, jet it up about 8 in the back. And go back to the track....
 

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I wouldve thought a "small" carb on a decent engine should be more sensitive to jet changes because its pulling harder on the venturi, yeah id probably put more carb on it but i dont think thats why its unresponsive to jet at the moment.
 

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I have just joined this site and kinda new to Drag Racing. I`ve been around my Dad who is all about D/Racing and he has helped me get to where im at now and I don't want to bother him cause I want to prove to him I can figure problems out on my own. I have a 3200 lb. 70 nova and it has a 383 with 220 cc heads, victor jr intake (ported to match heads) with a holly HP 750 carb. 302/296 adv. 270/263 @ .050 .600/.588 solid roller, 13.65-to 1 comp. with 1 3/4 headers, 5000 stall in a th350, 5.43 gear. now for the problem it has run a best et of 6.80 @ 100 mph. the car is busting out on the top end in all three gears. I keep putting larger jets but it still dose the same thing. I have 98`s in the front and 92`s in the rear. I run a holly blue pump with 7 psi @ the bowles. I have tried all I no to do and im in need of help. I know my dad could fix it if I ask him but I am wanting to do this on my own. thanks for any advice.

David
Plese explain "busting out on the top end in all 3 gears".
5.43's and a Turbo 350, wheelstands? What are the 60's? Is there a PV in this carb, HP's have them frt. and rear? Sounds like odd and too much jet. Is the timing locked and what is it at? What fuel? How many RPM's is this engine turning? what shiftpoints?
 

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Discussion Starter #10
again guys, stuck in stupid 92 ft. 98 rear. sorry for that. I run 110 vp fuel and I have a crank trigger on it (msd) and it is set at 30 degrees right now. it got quicker et`s with each jet change. it started out with 76`s in ft. and 82`s in the back. What I mean by busting out is it seems to be cutting out like it is running lean (something like a skip in all cyl. on top end) it deffinetly gets better with good air (colder). I was thinking a larger carb but dosent that allow more air (cfm) and that would make it worse. I barrowed (swiped and put back) one of my dads old carbs it was a barry grant gold claw carb, the one u can change the venturi size on and it seem to make it worse. I no it had the 750 venturi`s in it cause that's what my dad put in it when he had it on one of his sm blocks. It starts busting out around 4500 all the way up to shift point @ 7000 and I have a 7500 chip in it now.

thanks again guys
David
 

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If there is a bad plug wire it will make the rev limiter come early and erratically. Take care and try it without the chip.
 

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Discussion Starter #13
The ignition sys was my first thought but plugs, wires, cap, rotor, and another 6 al box and same thing. I even swaped the coil (thanks to dad and his spare parts). the pump is the blue holly with two earls filters in line all looked brand new. The pump has less than 10 passes on it. I cant remember the 60' times. The car is fairly new to me and I cant recall what it run. I will get an time slip and find out. It only had a pv in the ft. but not the rear. its a 4.5 pv since it idles with 6" of vac
 

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What plug gap?

Do you have a fuel pressure gauge so you can see the pressure at WOT?

That’s crazy big jetting unless you have a 4” stack of carb spacers. Do you have secondary jet extensions? If you really need that large a jet, which I doubt, screw-in jet extensions are so long they will reduce the flow of jets in the mid to high 90’s.

Some Holley Blue pumps made several years ago, (10-20) had brushes that needed a long running-in time to reach full contact and conform to the armature. They were made with the radius of the contact surface on the end 90° out of turn to fitting the commutator and so only made contact with the two narrow edges, limiting the amperage the motor could pull. They could maintain fuel pressure until they had to flow near full capacity. They can’t just be rotated to fit because the brush wires have to fit in a slot in the brush holder.

The solution is to use garnet paper (ask a starter rebuilder for some, a hardware store may have it) over something with the same diameter as the commutator and sand the brushes to fit correctly. Garnet paper is necessary because regular abrasives will impregnate the carbon brush and gouge the soft copper commuter segments.
 

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The ignition sys was my first thought but plugs, wires, cap, rotor, and another 6 al box and same thing. I even swaped the coil (thanks to dad and his spare parts). the pump is the blue holly with two earls filters in line all looked brand new. The pump has less than 10 passes on it. I cant remember the 60' times. The car is fairly new to me and I cant recall what it run. I will get an time slip and find out. It only had a pv in the ft. but not the rear. its a 4.5 pv since it idles with 6" of vac
just because its new dosent mean it works properly!!!!!!!!!! FLOW TEST AT CARB ENTRY!
 

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again guys, stuck in stupid 92 ft. 98 rear. sorry for that. I run 110 vp fuel and I have a crank trigger on it (msd) and it is set at 30 degrees right now. it got quicker et`s with each jet change. it started out with 76`s in ft. and 82`s in the back. What I mean by busting out is it seems to be cutting out like it is running lean (something like a skip in all cyl. on top end) it deffinetly gets better with good air (colder). I was thinking a larger carb but dosent that allow more air (cfm) and that would make it worse. I barrowed (swiped and put back) one of my dads old carbs it was a barry grant gold claw carb, the one u can change the venturi size on and it seem to make it worse. I no it had the 750 venturi`s in it cause that's what my dad put in it when he had it on one of his sm blocks. It starts busting out around 4500 all the way up to shift point @ 7000 and I have a 7500 chip in it now.

thanks again guys
David
30* sounds a little low on timing. Idle vac doesn't mean anything to PV's as no vac gets to the PV until the blades open. Either way remove the PV for tuning, if you want it later put it back in. If you're jetting you gauge by MPH, not et's. Need to check float levels and monitor down track fuel pressure.
 

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Discussion Starter #17
ok. Thanks for the input guys. I will check both fuel pump and flow. but how much should the free flow be? The back jets do have extentions on them. I have autolite 3924 plugs with a gap of .045 I will have to get a hose to see my pressure at WOT. guage is mounted on the regulator by the carb.

thank again
David
 

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Bracket racer
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Lean it up and put some timing in it....
 

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Bracket racer
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Also, check the rotor phasing....which means make sure the rotor button is pointed at the #1 plug terminal on the distributor cap at the point your timing is set.
 

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CHANGE! the pump it's not enough volume to support the fuel demand at higher rpm levels,I have run this combo for yrs i had a 388 stroker 14.1 compression with dart 210 runner heads with a 645 in 675 ex 110 lobe sep and 108 ic i had a blue holley pump on it and ran lean upstairs with a 950 hp carb from holley all the time.I found this after i burnt the chamber out of the heads i fixed the head and put it back togther with a aerospace components ultra flow 250 fuel pump with up graded an 10 lines from the tank to the pump and to the reg witch was the aero space reg to match with two single lines of an 8 to the carb after doing this the car ran it's best et of a 9.99 at 131 mph from a 10.30 at 124 mph in a all steal 68 camaro turbo 400 and 12 bolt with 488 gears please do yourself a favor and change the pump good luck killer 70 nova
 
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