Hey All Polaris Gurus,

I'm at my wits end with this 4 wheeler, and desperately need some help!

I'll give you the short and dirty background to avoid questions later...I bought a 1997 Trail Boss 250 from a friend last fall. It's been used and abused, but the price was right and it was in okay condition. It ran okay, but started a little hard. It would idle for 30 seconds or so, and then die if you didn't pull the choke for a few seconds. It did this even warm. Started hot or cold, warm or cold outside, though it needed choke to start (like the book says it should). Ran fine once it got going.

I'm pretty handy with a wrench, and have worked on 2-cycles and Mikuni slide valves before. Compression and spark checked out okay. We pulled the carb and cleaned it all out. There's nothing to these, so it was easy. Needle/seat, float, and jets all looked good. Put it together and it ran fine. No more dying out when warm, and started in all temps, even below freezing. Success!

Until... it sat for a few weeks and when I went to start it, no go. It would pop and backfire, but no start. Changed to new plugs, and same thing. Played with the screws and finally got it running, but really hard to start, and would flood out at idle or decel. This went on for a while.... Replaced choke, same thing. Replaced needle and seat, same thing (I can leave the fuel on, and it doesn't leak gas). Replaced all the jets, no change. Rebuilt carb 3 times, same. Turned screws, no change.

Here's where it is now: It's start fine when cold (left indoors), no choke, runs for a while, and eventually floods out. Change plugs, get it running, and it runs great, though it will pop on decel, sometimes die when I stop or at idle. At any time, pulling choke = BAD. Ride it around for a while, let it sit, and now it won't start at all. Change plugs, nothing. Pops, backfires, maybe runs for a few seconds but won't stay going. Inside warm or oustside cold (I'm in Wisconsin) doesn't seem to matter. Sometimes it will run okay one day, and won't run at all the next.

It just seems to be running uber-rich no matter what I do. Tried pulling the exhuast off in case that was plugged, but the spark plug fouled anyway. Tried closing off the choke, no difference. Tried really turning out the air screw (way past factory settings) and no difference. A couple pulls and the plug is wet. Double checked the float was at factory settings, same. No matter what I do same, same, same.

I'm really getting a little frustrated here. I'm not an idiot (well, I did buy a 12 year old four wheeler from a buddy....[img]i/expressions/face-icon-small-smile.gif[/img] ), and I've worked on this stuff successfully before. What am I missing here? it's got to be something simple. I'm really afraid to take it too a dealer/shop since they'll probably just do what I did all over, and charge me again for it. Worse, it will do the thing where it runs okay, but after siiting a while it wont' go again. Besides, not it has become personal! [img]i/expressions/face-icon-small-smile.gif[/img]

It's currenlty jetted for the correct temp (according to the book), though I have a cold weather jet. Tried both, no difference.

Any thoughts out there?

Thanks!
DEM

 

i have a 92 trailboss that was doing pretty much the same thing. what is your exact compression reading? mine was 100psi. i thought it was good enough. nope. tore it down. busted upper ring and gouges all over the piston.

 

might try a leak down test on it to see if there is an air leak. can cause lots of problems on a 2 stroker

 

<div class="FTQUOTE"><begin quote>Originally posted by: rockout

i have a 92 trailboss that was doing pretty much the same thing. what is your exact compression reading? mine was 100psi. i thought it was good enough. nope. tore it down. busted upper ring and gouges all over the piston.</end quote></div>

I think it was around that...can't remember though. What should the compression be?

Thanks,
DEM

 

115 min. i think 125 is preferres. doesn't seem like a big dif. or big deal, but makes a world of dis. on a 2 stroke engine. i had a dirt bike that wouldn't start worth a crap, low comnpression, rebuilt and starts on 2 kicks everytime. something about the higher compression being able to pull more fuel in and obviously compress it more.

 

<div class="FTQUOTE"><begin quote>Originally posted by: rockout

115 min. i think 125 is preferres. </end quote></div>

thats incorrect. the spec reading is 100 as the minimum. 115 to 120 is optimum

 

Random thought, what about timing? Or spark in general?

We haven't really checked it since it ran all right before and we never messed with it. We also assumed it was okay since when it does run, it seems to run okay. But could it run okay and still start hard/flood due to incorrect timing?

DEM