Recently my friends 97 Banshee suddenly developed a misfire at high rpm. The motor was running fine beforehand, so jetting is not the issue. The carbs have been removed and cleaned, the reeds checked (they are fairly new), the plugs replaced with working ones, and the tors system switches were checked. The slides are in correctly - Like I said, the engine was running very nicely and then suddenly developed the misfire.

The motor runs strong and smooth at all throttle settings as long as the engine is spinning lower than roughly 5000 rpm, at which point it sputters from the misfire.

I thought of replacing the cdi/coil with working units to eliminate that possibility.

Has anyone else had a similar problem? Or are there any of you well schooled tech guys out there that know what else can be checked???

Thanks.

 

Check out your wiring harness. If your bike if back firing its usually eletrical. Sometimes when you have a pinched or wire grounding out it will cut out only at high RPM. This is a very common problem, at least I see it alot at the races. Usually with the TRX250r, the owners of the bikes are too afraid to tear in to the wiring harness and try and shorten them up.

I've seen several top GNC pros wiring harnesses with the wires still going to the rear of the bike for the tail lights. This is ridiculous email me if you need to have your harness shortened. I'll do it for a small fee or fax you the plans to do it your self. (TRX250R only please)

Hope this helps

Waymod

 

I have heard of this before. Especially at high rpm's. The suggested fix was to try closing the gap on the plugs a bit. The high rpm's seemed to be blowing out the spark. Just an idea. Hope you figure it out.

 

We have experienced that problem with several banshees up here in NY and the cause that we have found on everyone is that the stator was getting weak. We replaced the stator and the problem went away.

JC Trx250R

 

Check the timing and the spark plug gap.

AMA 99 Sportsman

 

As an update - the tors box was disconnected and the problem still exists.

The stator seems like a distinct possibility. I may try swapping it out to see if it is the fix.


[This message has been edited by SandmanBlue (edited 01-06-2000).]

 

Another update - 1/6/00

After running a compression check, we found a bad cylinder. Only 80 psi compression. When the top end was taken apart, there was a broken top ring on that cylinder. The motor is getting a new top end. This is something we should have checked sooner. We'll find out soon if it was the problem.

 

Problem solved. The low compression and broken ring caused the problem.

For those of you following this, there's a lesson here. Run a compression check on the motor as part of the initial diagnoses. It may very well tell you where the problem is.