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Old 06-09-2009, 04:11 AM   #1
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jet size

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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Old 06-09-2009, 08:09 AM   #2
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Re: jet size

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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Old 06-09-2009, 05:27 PM   #3
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Re: jet size

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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.
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 ***) 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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Old 06-09-2009, 07:50 PM   #4
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Re: jet size

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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Old 06-19-2009, 07:11 PM   #5
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Re: jet size

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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Old 06-21-2009, 03:19 PM   #6
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Re: jet size

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.
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Old 06-22-2009, 02:11 AM   #7
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Re: jet size

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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Old 09-04-2009, 06:56 AM   #8
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Re: jet size

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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Old 09-04-2009, 08:29 AM   #9
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Re: jet size

good deal
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