motorpsycho
Active Member
Just a wild guess, but the screw that runs straight into the side/center of the carb is probably the idle adjustment screw. The easy way to find out is to remove the top cap of the carb, and pull the slide out. You should be able to look down into the carb from the top to see which one is the idle adjustment screw. The idle adjustment screw will be visible because it is tapered, makes contact with the slide, and it moves the slide up & down depending on which way you turn it.
I'm guessing that the other screw is an air/fuel mixture screw and it will affect the idle even tho it is not an idle adjustment screw. When you lean out the mixture (more air than fuel) the idle will go up without touching the idle adjustment screw. When you richen the mixture (more gas than air) the idle will go down without touching the idle adjustment screw.
When you turn the screw out (loosen it) this should make the mixture leaner.
When you turn the screw in (tighten it) this should make the mixture richer.
The trick is to find a happy medium with the air/fuel mixture screw so that the engine will sit there and idle without having to mess with the throttle or anything else, AND so that the engine runs strong and does not 4 stroke or bog under acceleration and at w.o.t.
It can be tricky to get it set right.
You want your spark plug to be a nice tan /carmel color, and you want your engine to idle good and run good with no bogging or 2 stroking.
If you have to keep messing with it you may have an air leak, because normally once you get the air/fuel mixture scew set where it needs to be, and the idle screw set to where it needs to be, you shouldn't have to mess with them any more. Maybe later on down the road you may have to tweak them a little due to wear, gas/oil ratio changes, or outside air temps. Generally, once you find the sweet spot of the 2 screws, any tweaks that need to be made to them should be very minor.
I have a cns knock-off carb called a wabro (no, not walbro), and it is very similar to the high performance carb with the air/fuel mixture scew, vent tubes and all that. mine works good, but it's jetted a tad too lean. I have been trying to find jets for it and the delorto jets that sick bike parts sells will not fit it.
So, i know that tuning these carbs can be a nightmare, but it can be done.
I'm guessing that the other screw is an air/fuel mixture screw and it will affect the idle even tho it is not an idle adjustment screw. When you lean out the mixture (more air than fuel) the idle will go up without touching the idle adjustment screw. When you richen the mixture (more gas than air) the idle will go down without touching the idle adjustment screw.
When you turn the screw out (loosen it) this should make the mixture leaner.
When you turn the screw in (tighten it) this should make the mixture richer.
The trick is to find a happy medium with the air/fuel mixture screw so that the engine will sit there and idle without having to mess with the throttle or anything else, AND so that the engine runs strong and does not 4 stroke or bog under acceleration and at w.o.t.
It can be tricky to get it set right.
You want your spark plug to be a nice tan /carmel color, and you want your engine to idle good and run good with no bogging or 2 stroking.
If you have to keep messing with it you may have an air leak, because normally once you get the air/fuel mixture scew set where it needs to be, and the idle screw set to where it needs to be, you shouldn't have to mess with them any more. Maybe later on down the road you may have to tweak them a little due to wear, gas/oil ratio changes, or outside air temps. Generally, once you find the sweet spot of the 2 screws, any tweaks that need to be made to them should be very minor.
I have a cns knock-off carb called a wabro (no, not walbro), and it is very similar to the high performance carb with the air/fuel mixture scew, vent tubes and all that. mine works good, but it's jetted a tad too lean. I have been trying to find jets for it and the delorto jets that sick bike parts sells will not fit it.
So, i know that tuning these carbs can be a nightmare, but it can be done.
Last edited:
