a little story, this was a pass around basket case on craigslist, no one seem to be able to get t run, they all seem to do a little work then sell it after about a month. i watched price bounce from 500 to what i got it for, 50 bucks.

it has new jug, head, piston, rings, plug, starter,fuel lines, carb rebuild, pep ****, battery and tires. well i got it now,

i did get it to run, but its very hard start, pull compression is 90 psi, using the starter its 64 psi, i tried the oil in the cylinder trick and thats what allowed me to start it, so at least not it starts, when running, it idles pretty good, decent throttle reaction, I understand it should have 120 psi, but with all this new, how could i get that, and what else should i look at . heads are torqued to 29, i forget where i found that spec. but thats what i set it to.

run down, it runs, drives, idles, but very hard to start and low compression with new parts.

 

90 psi is too low!! Looks like someone either put a used cylinder and stuck a stock piston back in or didn't bore it right for an over size piston. Oil in the cylinder just allows the rings to seal up against the cylinder long enough to allow enough compression for it to start. Once they start the rings loose seal against the cylinder wall and the machines either start running crappy or die or both. Do it right,pull the cylinder,have it measured for the correct over size piston and have it bored and honed.Then you ought to be able to ride and have a little fun.

 

I will check the bore, i did not do the piston, the kit that was used is, Namura Technologies, pt# NA-50000, 71.96mm, fits, 85-99 trail boss 250, 89-02 big boss 250, 90-06 trail blazer 250, 00-02 xplorer 250,

I dont have a telescopic gauge, but i will find someone that does.

 

250 std bore is 72mm so this is a std piston looks like.An easy way to tell is to pull the cylinder,pull the piston and rings off the piston. Just insert the piston into the bottom of the cylinder,hold the piston skirt even with the bottom of the cylinder liner and see what feeler gauge can fit in between the other side of the piston skirt and cylinder. If a .004 or larger feeler gauge can fit,time for an over size piston kit.

 

i will give it a try, i intend on taking the jug off tonight or tomorrow, I will post what i find. thank you for how to check.

 

bottom is 011 and top is 028 bore. it or replace it? im going to check prices in my area.. but what do you suggest?

 

Very lucky you didn't break a piston skirt with that much clearance at the piston skirt. A 72.50 (.020 over size) Wiseco should easily take any egg shape out of the bore and clean up ok.Be sure to check the bottom end also.http://www.ebay.com/itm/Wiseco-Polaris-TRAIL-BLAZER-250-72-50MM-Piston-Top-End-Gasket-Kit-1985-2005-/141543650398?hash=item20f4a8b45e&vxp=mtr

 

just checking in, i have been very busy moving a hobby farm, now that i have time again, i have been working on my arctic cat along with this polaris, Im thinking in the next couple days i will be ordering the piston,, probably more like tomorrow if my friend dont sell me his 4x4 tonight. i will be back with more info when i have it.

 

i said screw it, i just ordered the kit you linked. may 12 delivery date.

 

any chance of linking whats needed for lower end, i might as well just rebuild he whole thing.