Hello new to the site. I've recently picked up the sled knowing of this problem. The sled starts and runs great anything above half throttle it sounds like it's loading up or dropping a cylinder or cylinders. Cleaned carbs checked over clutching went through fuel pump and cleaned. Also while cruising the sled acts as if it's dropping cylinders it will not rev past 7k rpm and is lacking power. Plugs look good 120 psi acrossed the board.
I have the exact same model and year sled. If it isn't scary with WOT, it is isn't running right. You probably have done most of this stuff already. Is the gas good? What about the in tank gas filter? Is it jetted right? I have a shop manual can send the Yamaha recommended jetting. Is the exhaust clear? Critters can bring a lot of stuff into a nest. Same thing with the airbox. I have had that happen in both the intake and exhaust.
I took the tank off and cleaned it out well. The Exhaust is clear and has an aftermarket can on it that has been repacked. This started happening to my friend, it ran fine one day and the next it stared this and hasnt changed sense. The gas is completely new. The sled also has a new stator. I'm leaning towards ignition problems but I've never owned a Yamaha sled or delt with one so I realy have no clue other then the normal checks like I've done already.
I should add. I did raise the neddle clips to the center groves which would richin it up a bit and it seemed worse then them being lowered. The guy I bought it from had lowered them thinking it was to rich so I wanted it back to stock.
Being that the problem started suddenly, I would lean towards ignition, as long as the fuel system has been check out. I would ohm out the coils, both the stator and the external coils. The exhaust could also have a restriction, sometimes critters like to build nests in the muffler while the sled is in storage, and will make the sled act like it is plugged up and rich.
Here are the resistance specs for the Ignition coils and stator:
OEM stator or aftermarket? Makes a big difference! Does the sled seem to have any excessive vibration at idle? Dropping speed and lacking top end power can be an indication of a crank out of phase. Easy to test.
Most likely your issue is with the clutching or the plug caps, assuming you dont have a bad coil and the tors isnt activating.
Stator is gold plated oem. And I also feel it's ignition related. I've gone over all fuel supply and tank as much as I know too. Plug gap and what plugs should be in this sled? There are BR8ES in it now.
No vibration what so ever. Sled runs great at idle and just not for idle. When I cruse down the trail I can hear a cylinder or cylinders not firing correctly like a dead leg it's dragging around but ever once in a while it comes alive never on top end though. It has no where's the power it used too.
A couple of other suggestions. If you have not done so already, replace all the plugs. I don't know why, but this cured a problem I was having. The old plugs looked ok. I think the old ones just had really bad karma or something.
When it starts missing and feels like it is only running on two cylinders check the temperature of the exhaust tubes. Mine will actually idle well, almost perfect, on two cylinders. One of those hand-held, infrared, non-contact thermometers work great. If one pipe is cold the problem is isolated. At that point change the spark wire positions and see if that does not move the problem to another cylinder. That would point to the ignition. You can do this since all the coils fire at the top and bottom of each revolution and it doesn't matter what wire goes where.
Regards to your earlier post, when one cylinder doesn't fire there is not really any vibration. Just a loss of power.
If you suspect the tors just unplug the carb switch and connect the two leads together on the ignition side. They fit perfect. Kind of like the engineers at Yamaha intentionally made it easy to bypass the tors. When the tors activates there is almost no power. Its pretty obvious.
Hit the sticky section atop the yamaha page for an explanation or tors.
You should have br9's in there if your riding normal snowmobile temps and your jetting is correct. .7 to .8 is the gap and ngk's come pre gapped.
When the carbs were cleaned, did anyone check the screen filters under the needle seats? Is there a chance someone left out an o-ring on the fuel screws or didnt put them back in the correct orientation, like missing a washer?
Sure the clutch isnt sticking and overloading the power curve?
Thanks for the info. The clutching is stock and seems to be working correctly as far as I can tell. I don't think it's possible to run the way it does over such a broad rpm rang if it where clutching but I'm not a savvy sled tech either so it's possible that's a problem as well. I did notice that when I raised the needles to the stock possision it seemed to run worse at a lower rpm then it was before I had raised them back up so I'm guessing it didn't like the added fuel at lower rpm.
Up date.
Pulled carbs did find screen dirty cleaned thoroughly again. I did end up finding a parts sled and robbed all ignition parts from it and changed one at a time I also put the correct plugs in and the correct gap with no avail. I now believe the sled is running to rich from mid to full throttle for some strange reason. Everything is stock and set to stock other then the can which I checked over and is clear of any obstruction. Just to recap the sled runs great below mid throttle and starts good.
Ok I'm just under 120. I'm not certain on jetting the carbs haven't been messed with other then cleanings although the sled was running just fine until it stated this.
Any idea on where the plastic washer should be on the metering rod? Above the clip or below the clip?
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