1998 yamaha timberwolf 250 atv all of a sudden won't idle steadily - cleaned carb, fresh gas, new spark plug, new air filter. rpm fluctuates and engine will cut off if don't constantly fluctuate choke, any leads greatly appreciated. thx
Check the rubber boot that joins the carby to the engine to often have seen the hose clamps over tightened therefore creating a split in the rubber letting to much air in giving the rough idle eventually you wont be able to start it at all (have a good thorough look inside an outside of boot doesnt take much)
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Hi, Anonymous the carburetor throttle shaft wheel has two cables the cable closest to the right side of the bike is the throttle cable and the one closest to the left side is the idle cable. Right about the middle between the two is the idle adjustment bolt it faces out towards the air filter end of the carb . The engine should be at operating temperature with the enrichener off to set the idle between 950-1050 rpm. Turn the idle adjustment bolt clockwise to increases idle speed and counterclockwise to decrease idle speed. If you have access to your air fuel mixture bolt you may adjust it as well if not there is a video below on how to gain access, make sure you start with clean or new spark plugs. Gently turn the air fuel mixture bolt clockwise until it starts to bottom out "STOP" do not over tighten as it will damage the taper on the end, now back it out 2 full turns to establish a starting point start the engine and check the idle rpm's and adjust the idle adjustment bolt accordingly for 950-1050 rpm if necessary, adjust the air fuel mixture bolt 1/4 turn at a time and let the engine settle for about 10 seconds, clockwise for a leaner mixture and counterclockwise for a richer mixture you are seeking the highest rpm your air fuel mixture bolt can acquire without going past 3 full turns from bottom then readjusting the idle adjustment bolt back down to 950-1050 rpm If you can not detect any rpm change and can not stall the engine by turning the air-fuel mixture bolt all the way in then your pilot/low-speed jet is too big. Final adjustment should be made with a clean air filter mounted to the carburetor. For more information about your issue and valuable "FREE" downloads that you will need please click on the links below. Good luck and have nice a day. how to adjust yamaha yz125 carb Yamaha yz125 carb adjustments Yamaha YZ125N1 Service Manual OEM parts for Yamaha http://mybikemanuals.com/yamaha/yamaha-yz-owners-manuals
The starting hard and Idling problem sounds like carb needs cleaning. If this bike has moved from a different area it might need different jets in the carb. I might have jumped the gun the gas/oil mix ratio is very important check that first. your spark plug should be a golden brown when mixture and right jets are in. This might resolve the low end power if the oil mix is to rich or you might need piston rings. GOOD LUCK
plugged air filter
water in fuel (likely to cause trouble in all RPMs)
plugged main jet in carb
plugged fuel screen in fuel tank
faulty float setting in carb
faulty spark plug
It's likely a carb problem if the air filter is clean and the fuel is fresh and free of water. Condensation is a good posibility (water in the fuel). I would suggest pulling the carb and inspecting the cleanliness of the fuel in the bowl for water and dirt. If you find water, dump all the fuel and start fresh. If you find dirt, give the carb a good cleaning.
That was an atmospheric vent you found that should not have gas in it. If it does, the carb has over flowed. It probably needs to be cleaned with special attention paid to the needle valve and float assemblies.It is routed up high to prevent water and debris from entering it and clogging it up. It should have holes for it to pass through on the snorkel coming out of the air box behind the gas tank under the seat.