Bike won't start: First make sure you have spark and you have compression. Try to insure you have no air leaks, either in the manifold/carburetor area, or with two-strokes, the crank seals. Problems can also arise from a head that is not torqued properly. With other things eliminated, move onto the carburetor. Make sure there is a good seal between the carburetor and the manifold. Also, make sure you have fuel flowing into the carburetor bowl. We use Tygon fuel line and a Visu filter so we can see that fuel is flowing and that it has stopped flowing once the bowl is full. If fuel is coming out of the bottom overflow tube, the float needle may not be seating properly. Fixing this will mean removing the float bowl with the float needle and cleaning the needle and seat with a "Q" tip or something similar.
Since the starting procedure requires the choke to be on, make sure it is pulled up until it clicks into place (full choke). If it doesn't click into place it will close when released. With the choke up and using no throttle, kick the starter (or push the button). When an engine is cold it may take a few kicks to get enriched fuel into the cylinder, especially on two-strokes. However, if it hasn't started after a half a dozen tries, carburetion in the pilot circuit is most likely off.
Start by removing the spark plug to see if you have fuel getting into the cylinder. If the plug insulator is dry you'll want to richen the idle. First try turning the air screw in about half a turn and retry starting. If it still won't start, try switching to a larger pilot jet. If the insulator is wet, try turning the air screw out half a turn or so and try restarting. Still too rich? Try a smaller pilot jet. If none of this gets the bike started, you can call me with your symptoms and I'll try to help.
Please note: Neither the needle circuit nor main jet come into play when trying to start your engine. You just want to deal with the choke and idle circuit which is the pilot jet and the air screw.
Bike starts but won't idle: The good news is that it started, making it much easier to diagnose whether it is rich or lean. First, raise the slide with the idle screw to where it will idle. Now turn the air screw in and/or out. If it gets better being turned out, continue until you reach the the highest idle, turning the idle screw out to bring rpms down. With the air screw in the position of highest idle start turning it in to richen the mixture. If rpms decrease immediately, turn the air screw out until rpms go up again. You are looking for the sweet spot which is just before the rpms start to drop when turning in the air screw. Once found, use the idle screw to adjust the idle speed. If this sweet spot is with the air screw set between one and two turns out, you have the correct pilot jet. If the air screw is more than two turns out, switch to a smaller pilot jet and turn the air screw in about half a turn, and start air screw adjustment again. Conversely, if the air screw is less than one turn out, replace the pilot jet with a larger one and repeat air screw adjustment. Set properly, the engine will idle without instance. Blip the throttle slightly. The engine should accelerate smoothly and return to idle quickly. If the engine 4-strokes (for 2-strokes), turn the air screw out a little until it does not 4-stroke. If your 4-stroke stumbles, turn the air screw out, again unti it does not. If the engine is slow to return to idle, turn the air screw in a little to fix that. You will want to check the idle again and make small adjustments if needed once the engine is warm.
Engine bogs when given throttle or is ridden about half throttle: With the idle dialed in at operating temperature, you can check the other circuits, the needle and the main jet. Needle position can be changed to dial in mid-range, from 1/4 to 3/4 throttle. Symptoms of richness are 4-stroking for a 2-stroke and accelerating slowly, and/or some mis-firing. You lower the needle to lean out mid-range by moving the needle clip to a higher notch. Symptoms of leanness are back-firing, low power and/or slow return to idle. With these symptoms you want to richen the mixture by lowering the needle clip, thereby raising the needle. Once mid-range accelerates cleanly and returns to idle quickly, you have it dialed in.
Issues at full throttle: Beyond 3/4 throttle, the main jet determines the mixture. If the engine will not rev out or misses at or near full throttle, you will need to switch to a smaller main jet. If the engine lacks power or spits back, switch to a larger main jet.
The key to proper tuning and fixing issues is to deal with one carburetor circuit at a time and to make minor changes. If a change improves things, you are at least heading in the right direction. If things get worse, you'll know to go in the other direction. I've watched many people continuously blip the throttle, trying to determine what is off. This only confuses things as you keep changing circuits. Hold the throttle steady at different openings to determine which circuit is off and then deal with just that circuit. We are here to help with any and all carburetor issues. If you are struggling with tuning or any other problem, give us a call and we'll help as best we can. Carburetors can always be sent to us to check out if you believe something is wrong with them.
Under the 90 day warranty, you only have to pay to ship it to us. We'll fix or replace it and return it to you. If beyond 90 days, we'll charge you for any parts needed and shipping to return it to you, but there will be no labor charge.
