Carb/Tuning Issues....HELLLLPPPPP

OneLeggedRider · 09-24-2019, 05:43 PM

Carb adjustment basics and standards.

A VERY long time ago carb manufacturers realized there needed to be a standard adjustment/setting for the fuel mixture screw so your average mechanic could accurately tune various carburetors without much difficulty. And here it is, regardless if it's on a car, bike, lawnmower, etc..

The starting position is 1.5 turns out from lightly seated (don't crank it down), and then you turn the screw in or out until you achieve your highest/best idle rpm, and then you turn the screw back just far enough to detect the slightest rpm drop. If this setting is below 1 turn out from lightly seated you need a smaller pilot jet, if it's above 2 turns out you need a bigger pilot jet.

From there it's on to the main jet. Start with a medium jet size for the particular carb you're tuning (we'll say a 110 for the stock or clone carb) and see how it runs. If it bogs at WOT but runs better with a little less throttle you're probably too big on the jet size. If it runs better at WOT with half choke or sounds revvy and poppy, or if you notice your exhaust pipe is getting really hot, you need a bigger jet.

Once you think you're close then it's on to WOT "plug chop" runs (hate that terminology). Which involves bringing the bike up to operating temperature, putting a brand new plug in it, and winding out every gear at full throttle and then hitting the kill switch before you let off the gas and let it coast to a stop. If the plug looks white or an ashy gray then you need to go up a size. If the plug looks black and sooty you need to go down a size. What you're looking for is the porcelain around the center electrode to be a brown color and the outer part a dark color.

Now it's on to the needle (needle jet jet needle is the proper term). You would have already set this at the center C-clip/or stock position for the above tuning adjustments. If you feel a slight bog as you're twisting the throttle/coming off idle then you need to raise the needle/lower the C-clip. I personally raise the needle as far as I can go without getting dark smoke and losing acceleration characteristics, you're looking for a smooth transition.

And after all of that... you go back to the A/F mixture screw and fine tune it as previously described, and then do some overall plug readings to be sure all is well. You're bike should start well with minimal choking, not bog slightly at WOT, and shouldn't snap crackle and pop when you let off the throttle.

09-24-2019, 05:43 PM	#21
OneLeggedRider Join Date: Nov 2018 Location: Stockport, Oh. Posts: 1,442	Carb adjustment basics and standards. A VERY long time ago carb manufacturers realized there needed to be a standard adjustment/setting for the fuel mixture screw so your average mechanic could accurately tune various carburetors without much difficulty. And here it is, regardless if it's on a car, bike, lawnmower, etc.. The starting position is 1.5 turns out from lightly seated (don't crank it down), and then you turn the screw in or out until you achieve your highest/best idle rpm, and then you turn the screw back just far enough to detect the slightest rpm drop. If this setting is below 1 turn out from lightly seated you need a smaller pilot jet, if it's above 2 turns out you need a bigger pilot jet. From there it's on to the main jet. Start with a medium jet size for the particular carb you're tuning (we'll say a 110 for the stock or clone carb) and see how it runs. If it bogs at WOT but runs better with a little less throttle you're probably too big on the jet size. If it runs better at WOT with half choke or sounds revvy and poppy, or if you notice your exhaust pipe is getting really hot, you need a bigger jet. Once you think you're close then it's on to WOT "plug chop" runs (hate that terminology). Which involves bringing the bike up to operating temperature, putting a brand new plug in it, and winding out every gear at full throttle and then hitting the kill switch before you let off the gas and let it coast to a stop. If the plug looks white or an ashy gray then you need to go up a size. If the plug looks black and sooty you need to go down a size. What you're looking for is the porcelain around the center electrode to be a brown color and the outer part a dark color. Now it's on to the needle (needle jet jet needle is the proper term). You would have already set this at the center C-clip/or stock position for the above tuning adjustments. If you feel a slight bog as you're twisting the throttle/coming off idle then you need to raise the needle/lower the C-clip. I personally raise the needle as far as I can go without getting dark smoke and losing acceleration characteristics, you're looking for a smooth transition. And after all of that... you go back to the A/F mixture screw and fine tune it as previously described, and then do some overall plug readings to be sure all is well. You're bike should start well with minimal choking, not bog slightly at WOT, and shouldn't snap crackle and pop when you let off the throttle.
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