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Tune carburetor for rs250

How to set needle for lean or rich.

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If adjuster screw is towards the front half of the carb, clockwise = lean, anti-clockwise = rich. If screw is towards back half of carb, clockwise = rich, anti-clockwise = lean. Make small adjustments. If you can't get good results then change pilot jet.

Posted on Nov 26, 2013


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First make sure metering is set at the correct height. Depending on carburetor seat the mixture screws then turn 1-1/2 CCW as initial mixture setting. Once your engine is running and warmed up tune the idle mixture first half between too lean and too rich then do the same with the high speed at full throttle. Warning if the top speed exceeds the design top speed enrich to slow down. To set the max top speed it is best to a tach designed for small engines.

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How many miles?? The needle jet/jet needle (brass kit) may need replacing ...they wear out due to vibration and cause the spark plugs to turn black, get poor milage, and then "carbon foul".
Try running it without the air filter for a few miles.. see if that makes it run better. If so, I would replace the air filter and put a new brass kit in the carburetor.
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Fine tune your motorcycle before rejetting your carburetor. If it's still running too lean, you can replace the pilot jet as a first step

Remove the bowl at the base of the carburetor by unscrewing the screws holding it in place. Unscrew the pilot jet inside, but be careful not to strip it. The jet size will be on top.

5 Year/ unlimited mile warranty No up front core charge

Use a screwdriver to remove the main jet from the brass jet needle holder, which is also called the emulsion tube.

Put in a pilot jet that is one size larger. Replacing it with a jet two sizes larger will make your mixture too rich.

Tune the slow/idle settings before replacing the main jet. Replace the main jet with one size larger. The sizes are in increments of 5.

Put the bowl back on, and align the accelerator pump shaft and rubber boot.

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Before I can tell you how to lean your carburetor out, I need to know what kind of carb you have. But, there are other possible causes for your problem. The factory usually jets the original Keihin CV carb too lean to meet EPA emission requirements. The most probable cause is running the enricher too long while warming the engine up. The enricher on any carburetor provides an extremely rich mixture. So rich that it will foul plugs if allowed to run for too long. You should only use the enricher long enough to warm the engine to the point to where you can keep the engine running with the throttle grip. Once the engine will run with the throttle grip, simply idle the engine up and use the throttle grip lock to hold the throttle at this setting and push the enricher knob in. Other causes could be that the needle is not seating properly and allowing the carb to load up with fuel. If this is the case, you should have noticed that the engine is idling extremely rich and poorly. In this case, you'll have to at least drop the float bowl off and replace the needle and check the float setting with the new needle. The Kiehin CV must be positioned on an angle to set the float properly. If you still have reason to think that you need to change your carb's jetting, re-post telling me exactly what carb is on your engine.

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