Thread: Elementary Question

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Hey guys/gals.

How do you know its time to change your jets in your carb instead of tuning your mixture? I assume you tune first then if that dosn't work then you change jets?

I still havn't graduated to real men carbs yet lol.

Thanks!
-CJP

I'm going to guess that by "tuning you mixture" your talking about the mixture screws on the front of the carb. These will only adjust the Idle mixture.

Changes for anything off idle will have to be accomplished by jet and or step rod changes depending on the carb type. Also the rate that the enrichment circuits open can be tuned by power valve/step rod spring changes.

The first step should be to determine if the carb is functioning properly, that there are no vacume leaks and no flooding over. This should be followed by insuring the iginition is also operating properly, (no fouled plugs or bad plug wires.

Unless you have access to dyno and exhaust gas analyser the next best way to determine if the carb neds changes are reading the plugs. Check the net and you should be able to find some good references as to what lean/rich plugs look like.



First you have to determine which RPM range

Originally Posted by dhemi1

Hey guys/gals.

How do you know its time to change your jets in your carb instead of tuning your mixture? I assume you tune first then if that dosn't work then you change jets?

I still havn't graduated to real men carbs yet lol.

Thanks!
-CJP

With today's gas it is very hard to "read plugs".
What still works a little is make a hard pass for at least an 1/8 mile.
Kill the engine and coast to the side and pull the plugs.
Yes,you will burn the $hit out of your hands.
You are trying to shoot for a carmel to tan color.
If they are white than you have gone to far.
I would try 4 sizes at a time to even see any color change.
One word of caution DON'T LOCK YOUR STEERING WHEEL WHEN YOU KILL THE ENGINE!!
Just turn it one click back.

Oh okay. I see. I thought you had main metering adjustment screws aswell, like RC engines but those carbs don't have removable jets (molded into carb body), I see the point now. I really need to get a carburetor tuning book and Holley's tuning DVD

Thanks alot guys,
Appreciate it,

-CJP