We recently picked up a 1994 Timberwolf 250 4x4.
cleaned the carb
Got it to run "almost" perfect.
When I say almost, it fires up immediately and purrs like a kitten.
The problem......Top speed seems to be about 25 MPH. I need to get out a GPS to get a more accurate top speed
We have a recon 250 as well and it is about twice as fast.
It never bogs like its starving for fuel or like its running rich or lean.
I was barely able to drive it up my ramps into my truck.
Where do I look from here?
I am going to do a compression test today
Carb jetting??? I am at 6200ft before I head up the hill to about 7500ft


Thank you for any and all help

 

Compression is 65 warm

 

Sorry, check the 65. I forgot to do test at WOT
Compression at wide open throttle was 90

 

A bit low, check valve clearances, as Yams have a habit of loosing clearance. This normally makes them bad to start though. While you are at it, check valve timing too. I would suspect carb, is the plug nose black and sooty after the bike has had a run? Slight possibility of a plugged exhaust, uncommon on four strokes, but baffles can drop into the exhaust flow and cause this. Some Yams have rev limiters for neutral and reverse, faulty wiring can cause the limiter to work in forward gears too. However I think you would hear the misfire when the limiter kicks in.

 

So I took the carb apart again and did some tweaking and cleaning.
I messed up and when I put the mixture screw back in on the bottom, I screwed it in all the way and forgot to back it off.
Believe that means its running lean. Attached is a pic of the plug
Put it all back together and still runs the same - Maybe a little better.
My compression after running it around has bumped up to 100
I guess next I will figure out how to adjust the valves. I have seen enough youtube videos on it that it does not seem difficult other than pulling the plastic off and the tank.

Is 100 comp still too low?

Tired rings?
Piston?
There is absolutely no smoke ever when this is running

 

 

Have you installed the complete airbox unit? These machines will run lean wuth no power if airbox is left open. Some folks try opening up the airbox to get more power but this only makes things worse.

 

It looks as though this thing is bone stock.

 

Plug colour is not far off, maybe slightly weak, but I wouldn't have thought it would affect running that much. 100psi is fine, again slightly low but nothing to cause problems. Do check valve timing, it is fairly easy on most Yams as they have that big, easily accessible, cover on the side of the head. I am assuming you know the symptoms of clutch slip as this would cause the inability to climb ramps and limit speed in high gears, but the engine would be revving hard, and power not getting to the wheels, if this was the case.

 

merryman-
Clutch slipping actually sounds pretty close to my symptoms. I am pretty new to ATVs and have yet to have that problem.
How do I go about officially diagnosing that is the problem?
Is that a spendy fix?
Thanks for your help