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Carburetors Carb discussion and questions. Upgrading your Third Gen's carburetor, swapping TBI to carburetor, or TPI to carburetor? Need LG4 or H.O. info? Post it here.

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Old 04-11-2007, 09:51 PM   #1
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750 cfm proform carb body

I just replaced my carb body with one from pro form. It seems as if it took away from my bottom end but added a little bit up top. And whats with the adjustable air bleeds?? I;ve never messed with them before so how exacly do you adjust them?? also the car doesnt seem to have as good throttle response as it had and if i really get on it it bogs right at first then slams you back in the seat.....any holley tuning tips will help tons And another thing i noticed is when i had the carb apart all 4 jets were size 80, should the primary's be a few sizes smaller??......thanks
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Old 04-11-2007, 10:18 PM   #2
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Re: 750 cfm proform carb body

the main body doesn't hold the jets, the metering blocks do. You jet the car to what the car needs based on what the plugs look like. If there is a power valve in the front then the front would be 6-8 smaller than the rears, assuming the rear had it blocked off. Also, did you check to make sure you installed it properly? Any vacuum leaks? A bog is usually from not enough fuel, so the pump cams would have to be checked to be adjusted properly or the cam changed, and/or the squirter sizes changed.
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Old 04-11-2007, 10:50 PM   #3
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Re: 750 cfm proform carb body

Yeah there was a power valve in the front but all the jets were the same size. After i installed the body i did notice a slight whistling but when i placed my hand slightly over the carb it stopped. And how exactly can you install them wrong? I changed my plugs and they were all black which is obviously rich. I didnt mess with any of the pump cams or adjust them at all. Also with the 4 screws that stick out of the metering block, I was told to turn them all the way in, then turn them out 1 1/2 turns and adjust them from there. Is that at all correct? And what would the rear have blocked off? sorry for all the questions, this is my first time messing with a holley
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Old 04-11-2007, 11:12 PM   #4
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Re: 750 cfm proform carb body

you have a PV on the back as well?? how about some motor specs

usually when you increase airflow, you will lose a bit on the bottom and gain on the top.. but not sure if its as much as you say..
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Old 04-11-2007, 11:18 PM   #5
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Re: 750 cfm proform carb body

you obviously need to rejet the carb, i believe my proform 750 is running 76/84 jets right now, but each motor is different.
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Old 04-11-2007, 11:35 PM   #6
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Re: 750 cfm proform carb body

No there's just a power valve on the front. I bought the car with the carb tuned the way it was with the jets the way they were. Motor is a 383, afr heads with 2.080 1.600 valves, victor jr intake accel distributor.Not 100 % on the cam didnt get the specs from the guy i bought it from. And he told me it was a 383 so thats all i have to go by, I figure it is with that big of an intake valve. What about these adjustable air bleeds? How do I know to adjust them? When I have the air cleaner off and give it gas by hand, i can see more fuel being shot in from the primary squirter then the secondary squirter.
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Old 04-11-2007, 11:39 PM   #7
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Re: 750 cfm proform carb body

Air bleeds should be fine initially they can be switched for a better idle, but typically aren't swapped out. You set the mixture screws with a vacuum guage in gear with a hot engine, I'm sure you can find a post for that if you don't know what's going on. Was the bog present before? Did you adjust the acc pump linkage when you switched main bodies?
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Old 04-11-2007, 11:54 PM   #8
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Re: 750 cfm proform carb body

No the bog wasnt there before and i didnt adjust anything. Should try to adjust the acc pump linkage at all? Yeah i'll have to try and look up a previous post about that. What should i search for? And doesnt the color of the springs on the pumps have somthing to do with it like their stiffness or anything. I belive i have a red spring up front and a gold one on the back.
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Old 04-12-2007, 12:36 AM   #9
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Re: 750 cfm proform carb body

To adjust the acc. pump linkage, you are looking to take up only the slack between the arm and the head of the adjustment screw with the spring on it. Holley reccomends turning carb (empty of fuel) upside down and rotate the throttle to full open position. Using a feeler gague, slide it between the arm and adjuster with a .015" feeler gap. If it slides freely without squeezing the override spring, it is correct. If it still has movement over the full open on the throttle, you need to adjust it to tighter. After confirming the .015" gap, close the throttle and check for any free play. When you have fuel in the bowls, it will emmit some fuel lightly from the squirters with a light tap on the accel pump arm. Any free play will cause hesitation. Most likely you only have a PV on the primary MBlock. If so, you would need to have that jet smaller. You mention springs. On the rear this is possible if its a vac. secondary, but if its a regular Holley it should have a pump cam on the front. What model is it?
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Old 04-12-2007, 01:09 AM   #10
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Re: 750 cfm proform carb body

pump cams are plastic pieces on the side, not the springs that help the throttle snap closed. Perhaps looking on the summit racing website you'll see the part I'm describing. Does your stall and rear gearing match your cam? If not there will be a bog regardless if the stall is too small. Otherwise pump cam swaps and squirters are next on the list.
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Old 04-13-2007, 05:17 PM   #11
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Re: 750 cfm proform carb body

The carb is not a vac secondary and there are two pump cams and they are both pink. Now when i adjust the mixture screws, what vacuum port do i hook the vacume gauge up to? and how exactly do i adjust them if someone could briefly explain the procedures to me that would be awesome. Also I would like to change the power valve. I was told that you need to measure your manifold vacuum and select your power valve that way. How do you know exactly what power valve you need?? Thanks
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Old 04-13-2007, 06:00 PM   #12
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Re: 750 cfm proform carb body

there are a lot of holley setup web pages that can be found online. For that matter, holley has the instructions online for your particular carb that would show how to setup mixture screws and pick PV.
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Old 04-20-2007, 11:42 AM   #13
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Re: 750 cfm proform carb body

I'm not sure if this is right or anything, but when you pull vacumn off the carb with an automatic transmission, you put it in gear right? I'm getting around 8 HG vacumn at idle in gear.
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Old 04-21-2007, 09:51 PM   #14
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Re: 750 cfm proform carb body

After multiple tuning sessions at the track, the proform carb body didn't improve my quarter mile times/trap speeds any.

It does look better though;-)
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Old 04-22-2007, 01:23 PM   #15
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Re: 750 cfm proform carb body

craig that only means that for your particular combo, your old main body was not a restriction point.
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Old 04-22-2007, 09:47 PM   #16
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Re: 750 cfm proform carb body

Quote:
Originally Posted by xpndbl3 View Post
craig that only means that for your particular combo, your old main body was not a restriction point.
Yes, I agree.
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Old 04-22-2007, 10:00 PM   #17
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Re: 750 cfm proform carb body

from the looks of things, i suspect you need more cam.. you have a good build but a rather tiny cam for a 355..
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Old 04-23-2007, 08:24 AM   #18
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Re: 750 cfm proform carb body

I'm open to suggestions on a new cam. I've punched several different ones in to dyno2000 and not noticing any big gains.

sorry on change of topic.
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Old 04-23-2007, 08:42 AM   #19
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Re: 750 cfm proform carb body

I've had some pretty good luck with the cam i'm running. It's the Comp XE292H. I just like the way the extreme energy's open and close the valves so quick. Its got 244 244 at .050 and .507 .510 lift with 1.5's
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Old 04-23-2007, 11:46 AM   #20
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Re: 750 cfm proform carb body

if you look in the instuctions it tells you how to initially set up the carb fo rthe swap. the deal is the 750 main body flows better than the stock unit. you jet the carb to the main body. not the engine. i had 83 in the front and 84 in the back. wich is what the instuctions told me to do. i was running 7.20's and that got me to a 6.99 @ 99mph. take the power valve out and go with those jet sizes and see what happens. it don't hurt to try. also i had 37 shooters on mine.
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Old 04-23-2007, 06:08 PM   #21
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Re: 750 cfm proform carb body

Well i bought this body from somebody and i didnt get the instructions. I'll have to try what you said. But it's ok to take that power valve out? I know i'll have to get one of those plugs to put in there then. How exactly does the power valve work??
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Old 04-23-2007, 09:44 PM   #22
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Re: 750 cfm proform carb body

if you drive it on the street at all, don't pull the power valve it is needed for a street vehicle unless it's off the trailer, make a pass, then back on the trailer type deal. I think I have 78/84 jetting in my carb, but it's been a while since I've checked it.
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Old 04-24-2007, 08:09 AM   #23
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Re: 750 cfm proform carb body

thats why you jet it up. i ran 83 in the front. when if i had a power valve i would have run 73's.
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Old 04-24-2007, 12:41 PM   #24
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Re: 750 cfm proform carb body

running jetting that high on the street will foul out plugs all the time, that's why the power valve is needed if you're street driving it.
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Old 04-24-2007, 03:49 PM   #25
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Re: 750 cfm proform carb body

do what??? foul out the plugs all the time. i've ran mine for two years on the street like that and the plugs look perfect. light tan and quite new looking actually. i've heard of people sitting at an idle and fouling out he plugs but the jets do nothing at an idle.
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Old 04-24-2007, 03:49 PM
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