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Holly Help


Well-known member
May 18, 2001
1977 Buckskin
Me Again. I running a Holly 4165 spread-bore on my 77. After my smog inspection this pass week, the tech indicated to me, that the carb was running too lean. This carb has revers idle jet needles. This means, when you turn the idle needles in, (clockwise) the mixture richens. He had to turn these needles all the way in and it is still too lean. I was hoping if anyone out there knows, how to richen the "MIXTURE" adjustment on this type of carb. On a standard carb you would reduce the air bleed size. I do not what to do what woud seems the logical thing and drill these out and later find out, that an non-destructive method would have been better. I know that float adjustment is very important and as soon as possible, I will be checking that.

I don't claim to know allot about them but, could you just go with bigger jets?:gap
I am not sure primary side jetting would effect the idle mixture. The mixture needles controls things until the throttle opens to a certain point. Then the jetting to run the engine takes over. (What you are referring to.)
I appreciate your in-put and if others can help, jump in. I may-be wrong and if changing the jet size would richen the mixture at idle let me know.
drill out the idle feed restrictions in the metering body about .001/.002. go slow on the drill size as a small change in diameter makes a big difference in richness.
If you turned the idle mixture screws full rich and the carb is still idling too lean, first thing I'd do is take the carb apart and make sure you've got no problem with fuel varnish, combustion sludge or other contamination that has plugged-up or restricted fuel flow through the idle circuit.

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