I just finish mods to our Ttrailboss. Has milled head .020, wiseco piston, trail porting,34mm carb and clutch spring.


Took it out today and at any stable (speed 1\2 throttle) for more than 5mins it just flat out dies. Was starting back up just fine, but now wont start. the plug is dry and black/gray. I have a 200 main in the carb,and needle is on the 4th clip down from the top. everything else was left as is.

Any sugestions ???

I posted a pic of the plug on my page.

 

Can Anybody help ? Wheres Bubba [img]i/expressions/face-icon-small-smile.gif[/img]

 

I will try to help but I will need more info.
What is the colour of the spark plug, white, rust, black etc?
At what throttle position does it die, 1/3 1/2 etc?
Will it not start when cold or just when it is hot?
Is this a new carb? (I'm not a trailboss guy so I don't know what size stock is)
Was anything done to the breathing, air box mods, exhaust etc?
I'm guessing that youy problem is related to jetting so when you answer these questions I might be able to help.
Good luck.

 

The plug color is lite black/grey and dry. it has a pipe, no other air box mods.

the stock carb is 30mm and I put a 34mm on it. It was shutting off running at about half throtle. Ater it shut of lastime it no will not start at all. Was starting perfect before this happened.

Don't think it sized cause when it shut off, it just would just cost to a stop.
Like if you pulled the sparkplug wire off while it was running.

 

It would be a good idea to do a compression test to make sure all is OK mechanical wise. The black/grey plug is an indication your running too lean and if run this way too long then it is possible to burn out a piston. The correct colour is "rust". The compression test will answer that very quickly.
To get your midrange richer you can raise the needle in the carb if that's not enough possibly a richer needle is required. A larger main jet would also be in order as well as opening the pilot jet too.
Good luck

 

Will do a compresion check next. I posted a pic of the plug on my page.


Thanks

 

This may be a dumb question but does it have spark?

 

Yup great big spark and hurt too. Well did a compresion check and only got 60 psi with the carb held wide open. Something must of melted or broke a ring [img]i/expressions/face-icon-small-mad.gif[/img]

 

I'm not much of a mechanic....but I not completely stupid if given the proper direction. what is needed to do a compression test and what should I look for out of a stock 98 Trail Boss?

 

you will need a compression tester (gage) and a spark plug wrench. Some of the polaris' are hard to check compression without pulling the fuel tank. I have seen very few polaris 2 strokes that would run with less than 90psi of compression with the throttle held wide open during the test.

a good quick check for most compression problems is to remove the spark plug and pour a little motor oil in the plug hole. put the plug back in and see if it starts. if it does you need to rebuild the top end. the motor oil creates a film to "fill in the gaps", allowing a temporary compression boost.