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Old 12-28-2008, 11:17 PM   #1
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carb size

i have a 1980 mustang 302 auto with some motor work a high rise intake and a ratty cam and some other stuff it has a eb 850 4barel on it and it wont idel is that to big or what you think is wrong it runs mint from like 2500 up but just wont idel
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Old 12-29-2008, 11:21 AM   #2
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Re: carb size

THat carb is huge for that car.
Did it run before?
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Old 12-29-2008, 11:27 AM   #3
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Re: carb size

Based on Holley's carb selector formula, that 850 is monstrous for your needs. With their formula, assuming a 95% volumetric efficiency (ported heads, intake, etc), and a 7000 rpm redline, you are looking at a flow requirement of 581 cfm....so the "proper" size carb would be a 600-650.

I'm not up on my carb knowlege as I am just starting to learn about them with my 460 build...but I would think the carb isn't tuned properly is the reason you can not idle.
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Old 12-29-2008, 11:35 AM   #4
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Re: carb size

yes when it comes to carbs "bigger isn't better". keep in mind some big blocks came from the factory with two barrel carbs.
when you say it won't idle, what do you mean? it loads up, or it just dies as soon as it trys to idle?
as far as picking the right carb. you need to know what intake you have, what comp. ratio, what cam, and the specs. on the heads. Like valve sizes, intake runner cc, and combustion chamber cc.
you do want a vac. secondery carb. for the street. more then likely you just need to retune the carb. and my need to change jet sizes
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Old 12-29-2008, 08:09 PM   #5
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Re: carb size

ya he said it ran good 4 him other then it ideled at 1500rpms it wont idel at all i have to fether the gas to keep it running. the front vacum lines arnt hooked up eather there just pluged the to little ones.
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Old 12-29-2008, 08:22 PM   #6
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Re: carb size

it sounds like you have a vac. leak. With the car running spray the carb and the carb base down with WD-40 if the RPMs drop when you spray it you have a leak. Spray again till you find the spot where it is leaking. If that is not the case try adjusting the idle speed screw and the air/fuel bleed screws. also make sure the throttle cable/linkage to make sure it lets the carb. come to complete idle
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