Hey folks. Ive read all of the other threads on people with a slightly similar problem but none of the suggestions helped me. I have a 1999 Beartracker. It starts perfect and idles perfect. Put it in gear and it idles perfect but when i try to take off mainly on an incline it starts chugging and sputtering. If i let off the throttle it will idle back up, if i stay on the throttle it will die but will start right back up no problem.
It has a new everything ..coil, carburetor (replaced twice), tank petcock and filter, carburetor inlet manifold/ boot, CDI, air filter and sparkplug. Ive gone through the wiring harness for bad wires and connections, set the valve lash, repeatedly checked the carb although its brand new, battery voltage is good. Ive put an inline spark tester in and it appears to have good spark. I also ohmed out the pickup coil, it runs about 350. There are no restrictions in the air box tubes, no matter what i do i get the same result, changing the plug, adjusting the carb, cleaning the carb, changing the carb. It is a stock bike and im 230lb, this just started out of the blue. Any suggestions would be appreciated. And ive done a compression check. All is good there.

 

By "carburettor boot" are you referring to inlet manifold or boot between carb and airbox? Yams are prone to cracked inlet manifolds. Try it without the silencer (muffler) if you can, as a blocked silencer can cause this.

 

Yes the manifold. I guess where you live determines what it is called but yes we are saying the same thing. It is a new manifold/boot. And no i havent disconnected the muffler/ silencer to see if it helped due to the fact that this was basically an overnight problem. I think its a bit deeper than that.

 

On a four stroke engine, if the silencer blocks, it does it "overnight" as it is either rodents blocking the pipe or a baffle comes loose and turns so that it blocks the pipe.

The "power coil" on the stator is more likely to give trouble than the pickup coil, and as it "sort of" works, neither coil may show up as faulty on an ohms test.