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Old 06-24-2011, 04:44 AM
67Mustang Al.'s Avatar
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Holley 650 DP

Just wondering if someone has some info/links on Holley jet bore sizes. I have what i think is a 67 main jet from the primary side of this new stock standard Holley. From some data i found on the web the inside or bore size of the 67 should be .068" but when i tried to check the size of the 67 using a .068 " gauge drill it was far too large to go through the jet . It may be around .064 or .065".
My question is are there different series of jets for cruisng and racing as the series i found on the net are 122-67, diameter .068" .from "Ken's Speed Machine"
The way this 347 starts from cold with choke needed for about 4to 5 minutes and the odd crackle/backfire looks like its on the lean side of normal with 12 degrees of initial timing.
Cheers from downunda
Al.
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Old 06-24-2011, 11:49 AM
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Old 06-24-2011, 05:58 PM
67Mustang Al.'s Avatar
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Thanks for the link. Yes the 650 i have is correctly jetted according to the mumbers stamped on the jet. I found some comment that Holley jets need pin sizing as they are all over the place from new. So that would explain why the 67 jet i have is not .068 in bore size. To make it standard i will pin drill it and try it again before i change for a richer jet.
Cheers
Al.
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Old 06-25-2011, 02:31 PM
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Quote:
Originally Posted by 67Mustang Al.
Thanks for the link. Yes the 650 i have is correctly jetted according to the mumbers stamped on the jet. I found some comment that Holley jets need pin sizing as they are all over the place from new. So that would explain why the 67 jet i have is not .068 in bore size. To make it standard i will pin drill it and try it again before i change for a richer jet.
Cheers
Al.
The number actually represents what the jet flows- not necessarily the diameter of the hole in the jet, although they can be close to one another.

You may even find that a jet could flow less after being drilled out- something to consider when you go to modifying jet sizes. The length of the orifice along w/the inlet and outlet chamfer angles and finish are very important to what a jet flows, as well.
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Old 06-25-2011, 06:10 PM
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Quote:
Originally Posted by cobalt327
The number actually represents what the jet flows- not necessarily the diameter of the hole in the jet, although they can be close to one another.

You may even find that a jet could flow less after being drilled out- something to consider when you go to modifying jet sizes. The length of the orifice along w/the inlet and outlet chamfer angles and finish are very important to what a jet flows, as well.
HI 327
Yes that makes sense as some jets are relieved or tapered into the final bore size i think for increasing flow rate for whatever application.
The 67 jet should have a diameter of .068" according to Holley and the ones i have which are new are around .064,.065" so i am going to drill them out to .068 and see what happens. I have bought a 1/4 32tpi die so i will use my small lathe and turn up some spares and play around with size and shape. I have an air'fuel ratio meter so some guess work will be eliminated.
Cheers from downunda
Al
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