1987 polaris trailboss piston

My guess is that Chinese carburetor is not jetted or set up right. It may not even be opening fully. Ask in the Polaris forums. Top speed should be 45 mph.

https://www.google.com/search?q=2001+Trailboss+325

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Polaris won't start!! Lights don't work!! Fix for 2001 Polaris Trailboss 325 left handlebar switch. - YouTube

Polaris won't start!! Lights don't work!! Fix for 2001 Polaris Trailboss 325 left handlebar switch. - YouTube

2002 Trail Boss NO ELECTRIC at all... ' Polaris ATV Forum (polarisatvforums.com)

below show circuit breakers page 32
Electrical/Taillight Parts List - Polaris 325 MAGNUM 4X4 HDS A00CD32FA Parts Manual [Page 32] ' ManualsLib

This is not enough info to start. ..Hold the palm of your hand over the back of the carb and make sure its sealed against it... You need a helper to do this properly. The engine should pull on your hand inwards... if not....??
Did a shop or factory trained mechanic do the work? Are the reed valves able to open and stay closed? What does the compression gauge read? If you don't have one, beg borrow, buy, and/or take it to a shop and pay them to check it. Check it with the throttle wide open... with new piston and rings it should pump over 120+psi. ..easily.
Have the compression checked and then repost with the results.
Thanks!

My Polaris 500 did same thing. Had to
get a carb rebuild kit. Small plastic ring wore out and caused problem.

check an oem supplier like cheapcycleparts.com, they usually list cross-references to everything else the part fits.

Here's a link for parts info
https://www.google.ca/#q=polaris+trail+boss+250+pull+start
Being the mechanical sort that I am I would start by removing it from the machine and then try to determine how to dis-mantle it.
Some of these were rivetted together so may require some creative technical abilities to re-build.
Checking with the nearest dealer is always a good option.

DOWNLOAD POLARIS TRAIL BOSS REPAIR MANUAL

trailboss-manual.blogspot.com/
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Try this video: https://www.youtube.com/watch?v=8_HhKSY3Ro8 or http://www.ehow.com/how_7943998_change-drive-belt-polaris-atv.html

go to youtube and look for polaris belt changing vids. its pretty easy and they're all similar.

Look at your Magneto Flywheel , sounds it jammed .