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06-09-2009, 04:11 AM
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#1
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jet size
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roughly what size jets should I start with in a proform 650 race carb?
the engine is 30 over,has a crane cam with just over .500 lift,trick flow heads that are cnc ported, fms 1.73:1 roller rockers,rpm air gap intake( ported) 1-3/4 long tube headers,I picked up a 650 holley to try on it and i tried every adjustment possible but it would not idle. The carb was completely rebuilt at a performance shop known for its knowledge of holley carbs. after fighting with it for 4 days I decided to just buy new. The only thing we never tried was jetting it up(at that point i wanted to throw it in the trash lol)Any one have an idea of what size jet I should use as a starting point?
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06-09-2009, 08:09 AM
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#2
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Re: jet size
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Deranged
Join Date: Jan 2005
City: Largo
State: Florida
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proform is a knock off Holley products that has quality issues and false cfm ratings the jetting of the carb is relevant to the maximum air flow of the carb. . Wild camshafts will also reduce idle airflow and you may find that you have to do some tuning of the airbleeds to correct the carb. try going 1 size or get a Holley 4779 750 cfm has it's is more user friendly to tune.
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Mods-MAc CAI , True Dual Flowmaster 40,3.73 ,T-Lok, 25% UDP, 3/8 Phenolic Intake Spacer ,Steeda Tri-ax, SCT Chip/ Tune
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06-09-2009, 05:27 PM
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#3
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Re: jet size
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I have had 2 1050 proforms on my truck with 0 issues. where do you find the info on the quality issues(not trying to be an ass) just would like to see the info
I think I will start with a 72 or 74 main and 80-82 secondary |
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06-09-2009, 07:50 PM
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#4
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Re: jet size
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please come try to take my guns!!!!
Join Date: May 2007
City: Denham Springs
State: Louisiana
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that's what jet sizes I would start with. I have a 454ci BBC with a 750 CFM carb. I running 76 primary and 90 secondary. car runs 13.1 A/F cruising on the mains and 12.3 A/F at WOT. car is set up for the street and trying to get the best fuel mileage.
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06 GT custom mandral bent exhaust, borla mufflers, o/r x-pipe, SCT2, tuned by Wes@TPS, CAI, 4:10 gears, ZEX 150hp wet shot, 03chrome cobra wheels/ 11.76E/T at 115MPH & its my wife's car  1970
Chevelle SS 454 big block Old School 500hp 
Chevelle
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06-19-2009, 07:11 PM
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#5
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Re: jet size
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Registered User
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well after swapping out jets,squirters,power valves,and doing a couple old holley tricks like opening the idle circuits up in the metering blocks and drilling 1/8 holes in the primary plates it is no closer to running right then when it came out of the box. I am stumped.Only thing I haven't tried is stepping up to a 50cc accelerator pump.Even with all these changes it has a major stumble off idle and falls flat on its face, but if I put the 750 back on it will unhook in 3rd gear if you mat it,Any one have any ideas to try? |
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06-21-2009, 03:19 PM
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#6
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Re: jet size
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please come try to take my guns!!!!
Join Date: May 2007
City: Denham Springs
State: Louisiana
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leave the 750 on the car and throw the other one back in the guys face. The guy that built the carb may be a great carb builder, but the is still human and can mess up from time to time. Something is ovously wrong with that carb and it needs to be given back to the guy that built it.
__________________
06 GT custom mandral bent exhaust, borla mufflers, o/r x-pipe, SCT2, tuned by Wes@TPS, CAI, 4:10 gears, ZEX 150hp wet shot, 03chrome cobra wheels/ 11.76E/T at 115MPH & its my wife's car 1970
Chevelle SS 454 big block Old School 500hp
Chevelle
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06-22-2009, 02:11 AM
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#7
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Re: jet size
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Registered User
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haha oh its back at his shop, I'm done wasting my time with it I was just curious if any one else had ever run into something similar |
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09-04-2009, 06:56 AM
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#8
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Re: jet size
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Registered User
Join Date: May 2009
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update,I picked up a quick fuel 650 race carb, that has been matched as close as it can get to my engine combo. I love it the car even more now. |
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09-04-2009, 08:29 AM
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#9
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Re: jet size
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please come try to take my guns!!!!
Join Date: May 2007
City: Denham Springs
State: Louisiana
Posts: 3,472
Thanks: 16
Thanked 71 Times in 66 Posts
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__________________
06 GT custom mandral bent exhaust, borla mufflers, o/r x-pipe, SCT2, tuned by Wes@TPS, CAI, 4:10 gears, ZEX 150hp wet shot, 03chrome cobra wheels/ 11.76E/T at 115MPH & its my wife's car 1970
Chevelle SS 454 big block Old School 500hp
Chevelle
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