Hi mt pit bike is spluttering under acceleration i have tryed to adjust air screw with slight difference but it is still not smooth under power. bike is fk1 125 dont know if valve clearence would be the issue???

Depressing the throttle slightly we listen to the engine. If the engine hesitates to accelerate, the LO screw should be opened 1/8 of a turn. If we open the screw too much, the engine will not accelerate smoothly and start shaking (too rich of a mixture). In this case we should close the LO screw slightly. We repeat this procedure until the engine reacts smoothly when adding power. Meanwhile, a readjustment of the idle speed may be needed.

After the LO mixture has been adjusted, we proceed with the HI screw adjustment. After securing the paramotor, we open the throttle to full power. We turn the HI screw to the left or right until the maximum RPM is reached. From this position just a slight turn to the right should cause a significant RPM drop. This means the lean side of the mixture has been achieved. Immediately we OPEN the screw to the left to prevent the engine from overheating!


Let us repeat once again this critical step:


At full power we tune for maximum RPM, then we close the HI screw more, until a drop in RPMs is noticed. When the drop in RPMs occurs we open the HI screw again until we reach maximum RPMs once again, and then we open the screw more until we have a drop of 20 to 60 RPMs. In this position the carburetor will be perfectly tuned slightly on the rich (safe) side.


Next, we should close the throttle and recheck the idle and the LO screw adjustment. If the carburetor was tuned properly, the idle will return to the normal setting described above.

To put it in a nutshell, if the engine idles and accelerates smoothly, does not smoke heavily and achieves 20- 60 RPM below maximum RPM, the carburetor is tuned correctly.

Depressing the throttle slightly we listen to the engine. If the engine hesitates to accelerate, the LO screw should be opened 1/8 of a turn. If we open the screw too much, the engine will not accelerate smoothly and start shaking (too rich of a mixture). In this case we should close the LO screw slightly. We repeat this procedure until the engine reacts smoothly when adding power. Meanwhile, a readjustment of the idle speed may be needed.

After the LO mixture has been adjusted, we proceed with the HI screw adjustment. After securing the paramotor, we open the throttle to full power. We turn the HI screw to the left or right until the maximum RPM is reached. From this position just a slight turn to the right should cause a significant RPM drop. This means the lean side of the mixture has been achieved. Immediately we OPEN the screw to the left to prevent the engine from overheating!


Let us repeat once again this critical step:


At full power we tune for maximum RPM, then we close the HI screw more, until a drop in RPMs is noticed. When the drop in RPMs occurs we open the HI screw again until we reach maximum RPMs once again, and then we open the screw more until we have a drop of 20 to 60 RPMs. In this position the carburetor will be perfectly tuned slightly on the rich (safe) side.


Next, we should close the throttle and recheck the idle and the LO screw adjustment. If the carburetor was tuned properly, the idle will return to the normal setting described above.

To put it in a nutshell, if the engine idles and accelerates smoothly, does not smoke heavily and achieves 20- 60 RPM below maximum RPM, the carburetor is tuned correctly.

Could be some dirt or moisture in the carberattor try loosening the drain screw on the bottom of the bowl. If this doesn't work the carb needs a good clean.

Check there are no air leaks around where the air intake rubbers are at your carburetor. It sounds like your bike is running too lean or weak which means your air/fuel mixture is running on too much air and not enough fuel. This would explain it running smoothly when you put the choke on as the choke "chokes" the majority of the air from the carburetor and allows more fuel to flow through the carburetor creating a richer mixture. There will be a mixture screw somewhere on the carburetor which will allow you to either richen (more fuel and less air) or weaken (more air and less fuel) by turning the screw either in or out. Only adjust this by a small amount (about a quarter turn at most) at a time and try the bike to see how it rides each time. After adjusting the screw each time let the engine idle for about 30 seconds or so to let it settle to the new mixture setting before riding. There will be another screw on the carburetor which is your "idle" or "tick over"speed adjustment screw which adjusts how high your engine revs while the engine is "ticking over". Turn it in to increase idling speed and out to lower the idling speed. This will probably need adjusting as you change the fuel/air mixture. I hope this helps you and good luck :o)

hey mate could be a few things, dirt in the jet easy fix take petrol float off the carb clean jet with w..d. Or there are two screws on the carb one petrol and one air mix the one u want his the petrol one. this will be very close to the accelerator cable and will have a spring on it turn it clockwise. VERY SMALL MOVEMENTS u will hear the engine rev faster as u turn the screw. hope this helps ****

Take it to a different mechanic. Your carb needs tuning. Air/fuel mixture is not at proper setting. Look it up on youtube if you want to try to adjust it yourself. Pretty simple to do once you find the proper screw to adjust. Also, in your manual it might show or explain it.

First and formost make sure air filter is clean.Then start bike and warm up engine.with engine warm adjust idle screw(the big screw with spring around it)Turn clockwise to increase and counterclock wise to decrease.with bike idling properly the low speed air adjustment screw (small screw located just above fuel bowl on side of carb)Adjust in small increments 1/16 turns at a time till bike has smooth throttle responce.This screw contols air flow during idle and up to 1/4 throttle.From 1/4 throttle and up the needle setting on plunger inside of carb takes care of 1/4 and up.You usally dont have to mess with needle unless you do upgrades to get more power out of bike.But over time the low speed settings can change due to wear on idle needle and air needle.So thats why you have to make adjustments.If bike still dosent respond or idle correctly I would purchase carb rebuild kit and your problem will be solved.

Could be your cdi box or possibly coil. How strong is your spark?

my pit bike will not keep it revs for a long time so can some one help me it is my first pit bike