I recently purchased a 1995 Yamaha Timberwolf 2wd and have no history of the atv. The ATV will not stay running. It may be a simple card adjustment, but here is what I have done/troubleshooted:

1.) new spark plug(s)- verified gaps and tried different gap (range in manual is .024-.028).
2.) shot of carb cleaner and it fires and runs while cleaner burns off.
3.) checked petcock to make sure its in the 'on' position.
4.) Checked plugs after many attempts of starting.. looks like wet fouling after adjusting the idle screw (yamaha call it an idle screw) on carb.
5.) checked spark: it has sufficient spark

It sounds like fuel is not getting to the engine. I notice that on top of the fuel tank that there is a hole where a tube would connect. There is no tube connect as seen in other atvs. What doest that tube do?

Any suggestions would be greatly appreciated! - thanks

 

Someone please help me out if im wrong.......[img]i/expressions/face-icon-small-happy.gif[/img] It sounds like you might need to clean the carb......Jets, bowl, pickup tube............As for the hole on the top of the fuel tank.....Is it on the gas cap??? If so it might just be a vent tube.....as Isaid before, others can chime in[img]i/expressions/face-icon-small-happy.gif[/img]

 

Wow, you were right on.

I was hesitant of opening up the mikuni since my experience with carbs has been only on a briggs motor. But, it took 5 minutes to find the problem. It was the float valve...it was so 'varnished' that it sealed itself shut.. I had to be careful and pull it out with a bit of force. The valve looks fine, just needs cleaned.. I found a ton of yellow junk inside.

Hope this thread helps others who are hesitant opening the carb up-- it was simple for me. I will fire her up and let you know if she suceeds.

 

Awesome glad I could help[img]i/expressions/face-icon-small-cool.gif[/img] Aight, yes please let me know how she runs!!

 

Well, I put her back together, and then the opposite happens: fuel does not shut off in the carb..meaning that the float valve is now never shutting off, even when full.

I assume that it would be the valve seat, that is likely rubber and has dried up and cracked.

Does that sound like a logical place to start? I dont see how the mikuni could be an adjustable float, so the next best would be to have a better valve seat.

your thoughts appreciated.

 

I was able to bend the float to keep the float valve shut off when full. It took about 4 tries to get it to the right adjustment.

Now, the next question. I have to keep the throttle on in order for it to stay running. Should I just keep turning the idle scew until its hot enough? Also, when full throttle its a bit hesitant. Maybe the high speed screw? What are typical settings on those? I put both at 2 turns out to start. Which way do I go if at high speed it hesistates? When at normal speeds it pops and cracks on occassion as well. I just want to get her to tuned up so I can sell her.

Thanks

 

Ill get back to you about the turns of the others.........As for the Idle screw.... since you have to have the throttle to keep it running..like you said, you turn the screw until it will idle.....Let me know.........others can chime in also[img]i/expressions/face-icon-small-happy.gif[/img]

 

If the float needle valve was all varnished up, i would think the jet are as well. Did you clean anything else inside the carb, while you were in there? Check the pilot jet over good. It has the smallest pasageway in the carb, and its always the first to plug. Symptoms of a plugged pilot jet, are trouble with the idle. There is a very tiny hole, and if you look down the jet, like looking down a straw, you should see light coming thru. If you dont see light, its plugged. Sometimes its plugged so bad, it cant be cleaned...in that caes, just buy a new one, they are about 5 bucks each.
Then id start at 2 turns out from lightly seated on the mixture screw, and fine tune from there.
Heres a good article on jetting, you might get something out of reading it.
jetting

 

I did check all passages on the carb- taking apart and cleaning. It doesn't mean that I did not miss something though. I did see light in the jet- and made sure it did not have any debris in it. i will check the link for the tuning. Thanks guys!

 

I had the same problem with my ttr-125Le.It cant be a lack of fuel to the carb because if it was then it wouldnt keep running even if it was being throttled.The problem with my ttr was the pin needle valve or w/e it's called was worn.I would just replace the needle valve and see if that keeps happening.I had to turn up to idle up to like 3000 rpms just for it to idle on its own.I would recommend not riding it until it is fixed because we did not fix our bike immediatly and we kept riding it and the engine locked up.It may not have been the valve which made it lock up.It was probably a lack of oil or overheating.