Hello, I have a 3246 carb on a 66 427- 425 hp that runs rich at idle. I've adjusted the idle mixture to no avail, can any one tell me what the correct jet's on the primary side are suppose to be. I can't find the answer in any of the manuals I have, the car runs great except at idle . Symtoms : Real rich fuel fumes at idle, plugs are not burning clean. Thanks Jerry Murphy ( 3179)
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Re: HOLLEY CARB JETTING
The primary jets are not part of the idle circuit, and shouldn't really affect idle quality. What results do you notice when you fiddle with the idle mixture screws?
If adjusting the idle mixture screws does not seem to correct a rich idle, the problem usually seems to be one of three things:
1) A metering block gasket is leaking. I've not usually had this problem with Holley gaskets. I've always had this problem with the re-usable neoprene metering block gaskets that are available out there. The neoprene fuel bowl gaskets are good, but I've never had any luck with the neoprene metering block gaskets.
2) A power valve is leaking.
3) A power valve inappropriate for your engine is installed. This should only cause a rich condition if your engine is generating a vacuum signal below the kick-in point of your power valve.
Bill Baird -
Re: HOLLEY CARB JETTING
The primary jets are not part of the idle circuit, and shouldn't really affect idle quality. What results do you notice when you fiddle with the idle mixture screws?
If adjusting the idle mixture screws does not seem to correct a rich idle, the problem usually seems to be one of three things:
1) A metering block gasket is leaking. I've not usually had this problem with Holley gaskets. I've always had this problem with the re-usable neoprene metering block gaskets that are available out there. The neoprene fuel bowl gaskets are good, but I've never had any luck with the neoprene metering block gaskets.
2) A power valve is leaking.
3) A power valve inappropriate for your engine is installed. This should only cause a rich condition if your engine is generating a vacuum signal below the kick-in point of your power valve.
Bill BairdComment
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Re: HOLLEY CARB JETTING
THANKS BILL: When I adjust the mixture they seem to adjust ok ie' the eng dies when they are all the in and they seem to be doing there job. I changed the power valve, installed a new holley one for that carb and replaced both gaskets. the jets that are in now are #73's on both sides. I will readjust the mixture again and try that.Comment
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Re: HOLLEY CARB JETTING
THANKS BILL: When I adjust the mixture they seem to adjust ok ie' the eng dies when they are all the in and they seem to be doing there job. I changed the power valve, installed a new holley one for that carb and replaced both gaskets. the jets that are in now are #73's on both sides. I will readjust the mixture again and try that.Comment
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Re: HOLLEY CARB JETTING
Jerry----
I don't have my Holley references at hand at the moment, so I can't comment on proper jet size. However, from the sounds of it, I'm not sure that your problem is jet size-related. I'd try replacing your power valve first. I'll try to post later on jet size if no one else is able to help in the interim.In Appreciation of John HinckleyComment
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Re: HOLLEY CARB JETTING
Jerry----
I don't have my Holley references at hand at the moment, so I can't comment on proper jet size. However, from the sounds of it, I'm not sure that your problem is jet size-related. I'd try replacing your power valve first. I'll try to post later on jet size if no one else is able to help in the interim.In Appreciation of John HinckleyComment
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Re: HOLLEY CARB JETTING
How stock is your motor? More importantly, what kind of vacuum are you pulling at idle? When you replaced the power valve, what was its vacuum rating? It seems to be generally best to run a power valve that is rated at 2-3 inches (depending who you ask) below the vacuum reading at idle.
Bill BairdComment
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Re: HOLLEY CARB JETTING
How stock is your motor? More importantly, what kind of vacuum are you pulling at idle? When you replaced the power valve, what was its vacuum rating? It seems to be generally best to run a power valve that is rated at 2-3 inches (depending who you ask) below the vacuum reading at idle.
Bill BairdComment
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Re: HOLLEY CARB JETTING
Bill Thanks: My vacum at idle is about 15 to 16 '' , my motor is stock. I ran it today and it seems to be better. as for the inches of vacum on the power valve it was giving to me by a friend, new in the package by Holley , but it was unmarked. Thanks for the info.Comment
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Re: HOLLEY CARB JETTING
Bill Thanks: My vacum at idle is about 15 to 16 '' , my motor is stock. I ran it today and it seems to be better. as for the inches of vacum on the power valve it was giving to me by a friend, new in the package by Holley , but it was unmarked. Thanks for the info.Comment
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Re: HOLLEY CARB JETTING
Jerry, the 3246 carb is listed in the Chevrolet service manual for'66 as carrying a #73 jet in the primary side with a .076 jet in the secondary. This is a pass car version of the 3247 carb used on the corvette, which is jetted with a LEANER #70 jet in the primary. Note that holly says theat the numbers on it's jets are flow rated, not sizes, but I've always found the diameter to be within >001 of the stamped number. I think the other guys are right on re-the gaskets and the power valve, but I thought it was intresting that the Corvette carb is jetted leaner in the primary.Comment
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Re: HOLLEY CARB JETTING
Jerry, the 3246 carb is listed in the Chevrolet service manual for'66 as carrying a #73 jet in the primary side with a .076 jet in the secondary. This is a pass car version of the 3247 carb used on the corvette, which is jetted with a LEANER #70 jet in the primary. Note that holly says theat the numbers on it's jets are flow rated, not sizes, but I've always found the diameter to be within >001 of the stamped number. I think the other guys are right on re-the gaskets and the power valve, but I thought it was intresting that the Corvette carb is jetted leaner in the primary.Comment
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Re: HOLLEY CARB JETTING
Thanks to both Bill's and Joe for all the good information. Thats what's nice about the board, someone out there almost always knows the answers.
THANKS JERRYComment
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Re: HOLLEY CARB JETTING
Thanks to both Bill's and Joe for all the good information. Thats what's nice about the board, someone out there almost always knows the answers.
THANKS JERRYComment
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