Holley carburetor - mixture screw

[Cisco82]

Hi there,

it looks like i need to lightly adjust the carburetor , the mixture is a bit lean. I have a Holley carburetor , i just need a confirmation : if i turn the mixture screw counterclockwise i make the mixture richer , correct?

I suppose the screw is acting on the fuel line so if i turn the screw counterclockwise i increase the fuel flow and , considering the same air flow, i make the mixture richer.

Thankyou

[rickf]

That is correct. But to set it correctly you would turn the screw in until the engine just starts to stumble and then turn it out counting the number of turns again until the engine starts to stumble and then go back in half the turns you backed it out. This is considered best idle mixture and then you can teak it from there.

Just a side note, on the Zenith 13660 series carbs you would set them the same way but them back the mixture screw out 1/4 turn at a time to eliminate the dreaded "flat spot". When the carb, and the rest of the tune-up is set correctly I have never, ever had to run with the choke on with any 151 I have worked on.

[Cisco82]

Thanks Rick, i wasn't aware about the rule of the middle point between the two opposite conditions for Holley carburetor

I don't need to run with choke but sometimes the engine floods when i try to start it when the engine is still warm after a trip. i ve checked the spark plugs after a long run and it looks like the mixture is too lean , however i ll follow your rule, lets see how it works!

[rickf]

Francesco, That rule is for any carburetor, not just this particular one.

[Cisco82]

It is interesting since i was following the TM-20 1960 and it simply suggests to turn counterclockwise the mixture screw up to the engine runs smoothly starting from the point where the engine begins to lag. For the result will be the same but with a different procedure.

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[rickf]

Remember, these manuals were written for guys that had little to no experience working on vehicles. Yes, that adjustment will get you the basic setting, but will it get you the best setting? They just give the basics on most everything in those manuals, they are not going to give full classes on teaching automotive mechanics. As a lifelong mechanic I tend to tell people how to get the best out of adjustments when I can.

[Cisco82]

Superb , it is exactly what im looking for!