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1991 Yamaha Timberwolf carburetor fuel issue


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I have a Timberwolf that ran great for along time, it started to have starting problems I cleaned the carburetor and changed the spark plug. It starts but bogs down in third gear and going up hill. I put a new carb in same issue. I’ve messed with the fuel air mixture same issue. I’m at a loss any help would be much appreciated. 

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  • Admin changed the title to 1991 Yamaha Timberwolf carburetor fuel issue

Well.. you say it started having starting issues and so you cleaned the carby, but after that it's not making it up hills. which sounds like a different problem, and, if it only started after you'd worked on the carby, sounds like something you've done.

Then you put anther carby on and it's got the same issue, but which issue, the hard starting or the no power ? And are you really sure the new carby is good, like, did you take it off a running bike to try ?

It is possible you just need to clean one of the carbies really carefully and it will be fine..

It's also possible it's not getting enough fuel into the carby..  a dirty filter in the tank perhaps.

It's also possible the motor has low compression, worn rings or valves not sealing for some reason.. Perhaps the valves need adjusting.

My advice would be to check the compression, check there is plenty of fuel getting into the float bowl, which you can check by undoing the drain screw and watching to see it keeps flowing at a good rate, then I think you should clean and set up the original carby again..

When you clean the carby you need to strip it right down, take the float needle's seat out, and the emulsifying tube that goes from the main jet up to the slide's needle. Take all the jets out and clean them carefully. Blow through the air jets in the air intake side of the carby from the aircleaner side. Clean up the chamber the emulsifying tube goes in. Blow through all the places where fuel jets fit.

When you have it apart, check where it fits onto the manifold that there are no air leaks. It will either be a rubber manifold, check that for splits, or it will be bolt on, check that has an O ring and/or gasket. Once it's back together warm it up and adjust the idle speed and mixture to the best slowest idle possible.. then take it for a test ride.. On a test ride, be observant about how it goes, how much throttle you are giving it when any problems start to manifest, and how it responds if you ease the throttle off slightly.

Hopefully after that it will be cured. but if not then report back and we will see what else we can figure.. but you need to be methodical about the carby work, and when you are riding and observing it.. 

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Will it bog down in second gear running wide open long enough? Or on the same hill?

I kind of went through this on a kawasaki. 

Swore it was the carb. Found the fuel petcock was restricting fuel flow. Pull the hose off the carb, open the petcock and make sure it runs out of there like crazy. 

Another machine that I swore was fuel delivery/carb issue turned out to be a bad CDI. 

Drove it around with the spark tester seen in the link below to verify I was losing spark instead of fuel. 


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46 minutes ago, Mech said:

That's a handy tool alright Tiha.. I use a timing light for the same purpose but you can't ride around with the timing light..


I use the timing light in the shop, but do you have the same problem i do? 

when I get he engine reved up it is flashing so fast the timing light is constantly on. 

But stare at it long enough you will see a blip if there is one. 

The little inline tester is great when you have to ride it for 30 minutes before it acts up. I duct tape it to the fender where you can kind of see it with a quick glance. 


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  • 2 weeks later...

Well got another carb checked compression and that’s good. Checked to make sure fuel was running’s out of the line it was cracked the bowl plenary of fuel. It won’t kick over? I sprayed started fluid it kicks over then dies. I’m again at a loss any help appreciated. 

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Ok.. first question.. Is this thing a four stroke or a two stroke.. I think old ones were two.. But I'm not a yammy guy. If it's a two stroke, the crank seals may be leaking..

Then, if starter spray made it fire then it sure sounds like a fuel problem still..  Did it run for a second or two with the fluid, or just give one fire then nothing again ? If the later, then it could be a bad spark issue, but if it will fire for a few firings/seconds at a a time on the fluid .. carby ! Or, to be more accurate, the fuel's not getting in there. Are you sure the new carby is a good one, did it come off a running bike ? A lot of new aftermarket carbs are not dependable either, they aren't set up right.

And to recap.. you started with a hard starting problem, but then it changed into a easy start but won't get up the hill problem.. Is that right ? And that was after you'd cleaned the carby ?  And the new carby you put on then, are you sure that is a good carby ? Just because it's new doesn't mean it's good.. Or did it already have the hill problem and the hard start problem ? We really need to address one problem at a time, and do one step at a time.  Perhaps you need to go back to the original carb and start the process again. First get it to start, then sort the hill problem.

If that doesn't sound good.. well..

A badly blocked exhaust can stop air and fuel being drawn in, and it will stop it getting up hills or revving.. especially revving. . The pipes can flake and distort and block inside if they are double walled exhaust which a lot are. You could try taking the exhaust off at the head for a bit.  just swing it slightly away will be enough.

Have you checked there isn't a vacuum leak between the carb and the manifold. If it's sucking in air there it won't suck fuel, but the starter fluid, being squirted, might make it into the cylinder. It happens a lot when people take carbs off old bikes that the rubber manifolds split, or, the metal manifolds warp when the carb gets bolted back on with a new O ring, Since the problems have been changing since you changed the carb you need to check that carefully. Are you sure you haven't lost the O ring or gasket if it's a bolt on carb? It happens. Either the blocked exhaust or a vacuum leak could stop fuel getting in..

Really, depending whether you know these new carbs are good ones or not, I think I'd recommend cleaning and servicing the original carb and putting that back on, with a careful manifold check. The get it starting and idling, then ride it and fix any performance problems.. One step at a time, and only change one thing at a time if things need changing.

Have you cleaned carbs before ? Did you take every jet, and the long brass tube between the main jet and the slide needle out ? Did you check the diaphragm on the slide for splits.. they need stretching to find the splits quite often. Did you take the brass seat the float needle goes in, out, they can get blocked and some have a tiny filter above them.


Try and recall and see if you can answer some of these question I'm asking.. It would help me to help you if I had a clear idea of the way this problem has developed. At this stage, depending how long it will run for on starter fluid, I'm suspecting the new carbs are not good ones.. or they have an air leak at the manifold..

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thanks for the response. I’ll start from the beginning to help clarify what had happened. The quad ran great for along time. My son has been using the last year or so and he blew a tire maybe 4 months ago. It sat for about 2 months before I got around to changing the tire. When I started it up after changing the tire it started no problem but ran for about 1 minute then ran out of gas. Next day I put new gas in and it wouldn’t start. At that point I used starter fluid and it would run for 30 seconds or so. I figured maybe there was bad gas from sitting so I took off the carb cleaned it and put it back. I was able to start it drive it in 1st second gear but when I would get to 3rd gear or any incline it would fall on its face and die. I figured a fuel problem so I got a new carb not a Yamaha, changed the carb same problem. Got another carb not a Yamaha now won’t start. Checked for vacuum leak and o-rings they are good. I still think it’s a carb problem I think I need to get a Yamaha rebuild kit. I’m going to try that next. 

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Did you swap the Jets from your OE carb to the replacement? 

Chinese carbs are a crap shoot. I have had them with passages completely blocked and not milled into the housing. 

If you can go back to the OE carb

When it is bogging down in 3rd, what happens if you slowly start applying the choke? Does it improve any or immediately get worse?

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It does sound like a fuel problem, but it might be a blocked exhaust, or an electrical problem, possibly as simple as a crook sparkplug. 

As has been said in here many times before, the cheap aftermarket carbs are not tuned right.. They all need work it seems.  

I'm highly recommend you just put the original carb on. I very much doubt it's going to need any parts.

You should strip and clean the carb before fitting it, but you need to strip it completely. We really want to be absolutely sure the carb is right, then if it doesn't run right we can start looking at blocked exhausts and electrical problems. You need to take out all the fuel jets, and the brass emulsion tube that runs up from the main jet to the slide needle. You need to take out the mixture screw and blow through all the air jets and the passages in the carb body. You need to blow and look through the fuel jets. They should look round and clean. If they aren't round, sharpen a small bit of hard wood and gently ream them out with it.  You need to clean the tiny holes in the side of the emulsion tube, and you need to clean out the drilling the emulsion tube goes in. You need to take out the float needle's seat and check it's O ring. You shouldn't need to touch the slide needle unless you have had that apart before and there is a chance it's had the circlip moved. Just spin it in your fingers to make sure it looks straight, not bent. When you are putting it back together, before you put the bowl on, to test the float needle you tilt the carb on it's side so the float tilts away from the needle and start blowing into the fuel inlet, then slowly tilt it back until the float touches the needle and stops you blowing through it. The float should be about parallel with the bottom of the carby.. The metal part of the float should be about parallel. It should close off fully with very little weight of the float on the needle. 

Clean the air cleaner and oil it if it's meant to be oiled. Wring it out after oiling it, and wringing it while it's wrapped in a rag is best. It gets the excess oil out. Too much oil can make them flood.

Have a look at the plug. If it's got a metallic sheen to the porclain, a slight grey look, it might be buggered. Stale fuel can wreck them in just a few firings. If in doubt get a new one. 

With the original carb on you should undo the drain screw at the bottom and make sure fuel runs out fast when the tap's on. Try the tap in both positions. That tests the fuel tap and filters and that fuel is getting into the carb, and in at a good rate.

Then you should start it and warm it up and adjust the mixture and speed. The idle mixture needs to be set with the slide down as far as possible. You speed up the idle till it will idle, then adjust the mixture to give the highest speed, then back the speed screw out to a slow idle and then re-adjust the mixture to highest speed again. You keep doing that till the mixture screw is in the center position between starting to slow because it's getting lean, and staring to slow because it's starting to get rich, and all with the idle as slow as possible for a steady idle. Then check the choke works, and that it closes right off and doesn't effect the idle.

Then you go for a drive and see how it goes. If it plays up, try and detect how much throttle it gets to before it starts misbehaving. There are certain points where the mixture is controlled by different jets. The points are, idle, idle up to about a quarter throttle, a quarter to about three quarters or seven eights throttle, and near full to full throttle. If it starts to falter then just hold the throttle steady and note what happens for a few seconds, then ease the throttle off very slightly and see what happens.. Take careful note of these things because they are important and will tell us what the trouble is.

Hopefully with a clean air filter, clean fuel and carb, and a new plug it will be cured. If not, get back to us and we will figure out what to do next.



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