1986 Polaris Trail Boss 250 2-stroke

[louie110]

I have a 1986 Polaris Trail Boss 250 with a 2-Stroke engine and recently this year I started it up and took it for around a ride of bout 6 miles. Then I got stuck in about a foot of snow and reved it up trying to get back out, although not extremely reving it up. Once i got out on the way back and going up some hills it began to really run awkward. I had hardly any power when I would increase the throttle. I took it home and worked on it. I first pulled the spark plug and it was completely dry and then replaced the in-line fuel filter and drained all the old gas. I thought it may be the carburetor gunked up so I went to the autoparts store and told me to put some "SeaFoam" in the gas tank and it would run like new. I did that and ran it with high octane gas. I checked the air filter and still ran terrible and was also backfiring badly ( out of the carburetor and exhaust) I took to the shop and they said there was fuel in the cylinders ( I don't think he took honest look at it ) They wanted $500 or more to fix it, I decided to look at it some more and go somewhere else for help. I searched the internet for awhile and read something about fuel in the crankcase. I opened the drain on the crankcase and tipped the ATV over and drained all the fuel. I popped the sparkplug and ran an air compressor in the head and also the crankcase to dry the fuel up inside. Started up great but still had low power and wasn't backfiring. I took carb off and cleaned and made sure floats weren't sticking. I took the needle out of the carb and cleaned it ( The needle did not look right such as maybe it was bent, would this cause problems when idling and running?) Now, I have good power but DOA when I stop. I have to hold the throttle just a little bit to keep it running or it dies. I believe I need some tips or specifications on Air/Fuel Mixture screw also the Idle Screw and also the choke adjustment on the carb. If you can help in any way I would greatly appreciate it. My toy is old but I am unable to afford new, just need a couple more years out of it. Thanks Alot

[SUKIJONES]

if you don't get answer on your Polaris try this site......http://www.gen3usa.com/

[Mudstock]

<div class='quotetop'>QUOTE (louie110 @ Mar 30 2007, 12:18 PM) <{POST_SNAPBACK}></div>

I have a 1986 Polaris Trail Boss 250 with a 2-Stroke engine and recently this year I started it up and took it for around a ride of bout 6 miles. Then I got stuck in about a foot of snow and reved it up trying to get back out, although not extremely reving it up. Once i got out on the way back and going up some hills it began to really run awkward. I had hardly any power when I would increase the throttle. I took it home and worked on it. I first pulled the spark plug and it was completely dry and then replaced the in-line fuel filter and drained all the old gas. I thought it may be the carburetor gunked up so I went to the autoparts store and told me to put some "SeaFoam" in the gas tank and it would run like new. I did that and ran it with high octane gas. I checked the air filter and still ran terrible and was also backfiring badly ( out of the carburetor and exhaust) I took to the shop and they said there was fuel in the cylinders ( I don't think he took honest look at it ) They wanted $500 or more to fix it, I decided to look at it some more and go somewhere else for help. I searched the internet for awhile and read something about fuel in the crankcase. I opened the drain on the crankcase and tipped the ATV over and drained all the fuel. I popped the sparkplug and ran an air compressor in the head and also the crankcase to dry the fuel up inside. Started up great but still had low power and wasn't backfiring. I took carb off and cleaned and made sure floats weren't sticking. I took the needle out of the carb and cleaned it ( The needle did not look right such as maybe it was bent, would this cause problems when idling and running?) Now, I have good power but DOA when I stop. I have to hold the throttle just a little bit to keep it running or it dies. I believe I need some tips or specifications on Air/Fuel Mixture screw also the Idle Screw and also the choke adjustment on the carb. If you can help in any way I would greatly appreciate it. My toy is old but I am unable to afford new, just need a couple more years out of it. Thanks Alot[/b]

You are going to need the manual for these adjustments. Sounds like you messed up the carb adj. Make sure Choke isnt stuck also. You can find a manual at the following Link: http://www.bigbuckatvproducts.com/po...odels_1986.htm

[superchicken]

signs of a dry plug is no good.....sounded like it was starving for fuel...the adjustment screws will only be fore idle so at worse if you fouled them up it wouldnt idle very good...but still would be drivable at 1/2 throttle or beter...with it being in storage for that long I would venture to say 1 of two things happened....carbs varnished up blocking the jets or a intake or base gasket blew causing a air leak...

[louie110]

Ok so today I took another step forward. I got the ATV to idle pretty good by adjusting the 3 adjustments to the carb. ( The choke adjustment, Idle screw, and the Air/Fuel mixture and I found and article online to give me an idea of about where they should be adjusted. For the first time in awhile I finally got it to idle and not die but when I am riding it, the atv has power and gets up to speed pretty well but engine cuts out. Tomorrow I am going to do a compression test and see if that could lead to a bigger problem than I think it is. Also when I adjusted the idle screw, it dies in any other position other than all the way in.


Here is the carb adjustment I tried. Found from http://www.repairfaq.org/samnew/lmfaq/lmadjc.htm

" Then slowly turn in the low speed jet, until it starts to die, then back it out another 1/4 to 1/2 turn. Then hold the throttle wide open, and slowly turn in the high speed, until it really starts to smooth out and rev high, and start screaming, then back this out until it starts to run rough or slow down, and then turn it back in to midway between these two positions. Keep playing with the low speed needle until you get rapid immediate response from the throttle, and good idle with the idle adjustment. Then play with the high speed needle, but always back it out from the setting about 1/4 turn or so, from where it runs the smoothest. This setting of backing it out will allow more fuel when under a load, and keep your 2 cycle motor from running too lean. Put a load on it and just tweak the settings just a hair at a time. "



If you have any ideas what may cause this let me know.


I am also going to replace the spark plug and find the correct gap and I am putting a full charge in the battery overnight, because I head some four wheelers and motorcycles run poorly or rough if they have a low battery.



Thanks to everyone involved!

[superchicken]

the problem with that article is that it is for small engines like a weed wacker..they have a low and high speed air scews...your carb only has a low speed screw that only helps with idle and off idle response....if you have got it to idle decent and good throttle reponse off idle''when you strab the gas i doesnt die or stutter'' leave it be...

cutting out on top end..
theres a problem in the main jet circut...a 2 stroke will surge and cut out when its lean..

lean = no fuel+running it= engine damage

next time it cuts out dont try to start it,pull the plug and see if its dry white and ashy looking....if it is,you have a main jet circut problem...clogged most likely..easy to fix..pull the carb off and remove the float bowl..the main jet will be in the center hanging the lowest if turned right side up...a wire bread tie is good for cleaning them out..I have even seen a main jet loosen up and end up at the bottom of the float bowl and cause the same thing your getting..

compression..if it starts easy I wouldnt be concerned as of right now..but get it fixed cuz every time it cuts out on you your basicly running the engine dry..

[louie110]

I had some help today trying to identify the cause of the cut outs and so we pulled off the exhaust and pulled the pull start to move the piston and be able to see if it was burnt out. From what we saw in the head down the sides of the piston were black. We pulled the head off and got a better look at the piston. The piston is black all the way around, about 2 inches down from the top. The piston rings were not scorched in place. There aren't any gashes or scrapes. Also the jet needle to the carborator is bent and also looks worn, I am not sure whether Polaris uses jet needles that look like this or not, I am planning on buying a new jet needle sometime this week and also let me know whether the piston is a total gonner or not. Thanks

[louie110]

I bought the new jet needle. and put the engine back together with new piston rings and got the head re-bored. It is running pretty good, no more backfiring or smoking. Made good progress. The problem now is I cannot get it up to full throttle without it losing speed, and backfires if you use the throttle after it slows down in the high range throttle. It has to either be the choke adjustment, idle screw or mixture screw. Also, if anyone knows, it says it has something like a reverse limiter, I barely even reverse and was wondering what the ATV means when it talks about that.


Thanks Again

[JCelentano]

<div class='quotetop'>QUOTE (louie110 @ May 18 2007, 06:40 PM) <{POST_SNAPBACK}></div>

Also, if anyone knows, it says it has something like a reverse limiter, I barely even reverse and was wondering what the ATV means when it talks about that.[/b]

I have a 2003 Trailboss and it has a reverse limiter also. What that means is that if you put it into reverse gear, the engine sort of misfires on purpose to keep you from going so fast as to be dangerous. On the engine stop/headlight switch setup there is a yellow button you can push to give it full power in reverse. If you do that, watch out. The first time I did it I went so fast I thought I'd get thrown off. I really wasn't expecting it to be so powerful. I guess it's because it's an automatic and it can go full speed, whereas my Warrior is a manual and is in low gear in reverse.

Anyway, I doubt it has anything to do with your problem...

Good luck!
Joe