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Hi, Jamie it should be noted that your performance issues are not electrical ie. faulty charging system, battery condition, and connections etc. If your fuel system (gas tank, filters, fuel valve and carburetor) is contaminated with ethanol sludge, varnish, rust, dirt, water etc. or your bike has been sitting for months or years without running these components must be "PROPERLY" cleaned and reassembled "CORRECTLY" before any adjustments can be made. Tuning your carburetor is fairly simple once you understand the basic principals. You engine is a simple airbox sucking air in and blowing it out, it is finely tuned at the factory for maximum performance once you upset that delicate balance by changing air filters, camshafts or exhaust systems your performance may go down the and the engine may run poorly, you need to compensate the air-fuel mixture in the carburetor in order for the engine to run smoothly and at peak performance. If you are running multi carburetors you need to sync them first and make sure your air cleaner element is clean and dry for paper elements or lightly oiled for foam and meshed elements and properly installed. Here is how and where you compensate trouble: "TIP" if your engine "BOGS" your not getting enough fuel.
1. Closed to 1/8 throttle is managed by the air screw and pilot/slow jet.
2. 1/8 to 1/4 throttle is managed by the air-screw, pilot/slow jet, and throttle slide.
3. 1/4 to 1/2 throttle is managed by the throttle slide and jet needle.
4. 1/2 to 3/4 throttle is managed by the jet needle, needle jet, main jet, and air jet.
5. 3/4 to wide open throttle is managed by the main jet and air jet.
6. Wide open throttle is managed by the main jet.
If you are running lean, spark plug electrode color is white, engine runs hot and feels like it is starving for fuel you need to go up on the jet size or move the c-clip down one notch. If you are running rich, spark plug color is black or dark gray, engine runs cool, and bogs down when accelerating you need to go down on jet size or move the c-clip up one notch. When your carburetor is properly tuned for maximum performance your spark plug electrode will be a light tan color like coffee with cream. If you prefer fuel economy over performance you can go down on main jet sizes until a satisfactory level of lower performance is acceptable versus MPH, your spark plug color will be whiter and your engine will run warmer. These tuning adjustments will only make improvements if your intake and exhaust system have no air leaks or sealing issues and the entire electrical system is in proper working order and you have no mechanical issues. For more information about your issue and valuable "FREE" downloads that you will need please click on the websites below. Good luck and have nice a day. Yamaha yz125 look over and carb help MototipsTV Replacing Float Cleaning Carb YAMAHA YZ125 Owner Service Manual OEM parts for Yamaha http://mybikemanuals.com/yamaha/yamaha-yz-owners-manuals
The screw I think you are adjusting is the idle mixture screw, and will only make a differnce at idle You set at the smoothest idle . If power in 1 and 2 is the problem, then there is something else, make sure the carb is clean, the exhaust is not blocked , the air filter is clean and relatively new,valve clearances? are ok, new spark plug , new oil, and then start looking at the jetting. up to 1\4 throttle -pilot jet around mid range -needle position top end -main jet. try riding with and without choke to get some idea, if it runs better with some choke then it is lean
i know you would like a simple solution. these saws are not simple. check gas for water, clean air filter, check exhaust. take carb off and clean all jets. spark, gas in, exhaust out. fuel line clear? i have seen these **** up so much dust it plugged the breather. hope this helped.
it sounds like you need to richen up your system. are you sure you have the clip in the right position. 4th from top or 4th from bottom? if it's in the correct position, try adjusting you mixture screw to allow for either more fuel or less air.
Is it the 01 we're talking about here? The carbs sound like they need to be jetted. Did this just start happening or did you move? Just buy the bike from another state? Does it burn rich when it does run? Does the exhaust burn your eyes? I had a hard time getting my 99 750 to run right, the factory set jets didn't work so I bought a jet kit from Dynojet, and it worked perfect. It is adj also, so if you move up into the mountains you can adjust your carbs. Also had one of those fancy air filters on there, had to take it off, cause it didn't work right either, went back to stock.
when you put on a new air filter you have to rejet the carb in order for the air/fuel mixture to be correct,because with a aftermarket air filter it is allowing more air in than before and not enough fuel. as the piston speeds up upon exceleration the air is not getting burnt off into exhaust because you do not have enough fuel in the mix
Running well at high revs would indicate that all the fuel and air it needs are getting to the engine and you also have a good spark. Probably no problem with air and fuel filter ( if fitted) or sparkplugs.
Running hot, and bad idling are signs of a lean air fuel mixture. The engine is probably not getting enough fuel at low revs.
This could be caused by an air leak between the carburettors and the engine. Check that the vacuum line to the fuel tap is properly secured at both ends. It is behind the fuel line at the tap.
Get a a short length of hollow plastic tube and use it like a stethascope - put one end to your ear and move the other end around your carburettor mounts with your engine revs as low as you can get, and listen for any sucking noises that would indicate a leak. Look for cracks in the rubber inlets.
The other possibility is that there is an internal blockage in the idling jets or idling fuel circuit. This is where dirt tends to lodge because the jet dimensions and passageways are very fine - The high speed jets are much bigger and dirt often just passes straight through.
Try a little bit of choke while the engine is warm to see if you get a stronger low speed response. If so that would point to an internal blockage.