Hello thanks in advance for any advice. Had some great weather in my area this weekend so took out my freshly rebuilt trailboss 250. Ran great however after about 10 minutes of riding bike would die and not restart unless you let sit for about 5 min. I've narrowed it down to the carb not getting fuel when it dies I cannot blow air into fuel feed line to carb when it acts up. Acts like float is stuck in the upward position or the needle and seat is stuck closed. Carb is very clean no dirty anywhere i've checked float level several times and float level is at spec. Any Ideas i'm leaning towards carb overhaul and replace needle and seat. Bike was a basket case when i got it so who knows how it ran last time it actually ran.

 

Make sure the tank vent is open. Follow it to the handle bars as most vent tubes are crammed down there and can get pinched. Other things to check are the atmospheric vents on the carb are open also. Kinda scares me though when I hear about one that runs for while and dies,starts back up later. Even though you said it's rebuild,recheck compression. Also check that the fuel valve flows good in the on position and also reserve. A lot of people overlook this. If everything checks out,then may just need a carb kit. Shindy is the best and several on ebay. Guess you have an earlier Trail Boss or Trail Blazer? 2001 Trail Boss was a 325 4 stroke.Shindy Carb Repair Kit for Polaris Trail Blazer 90 95 250 2x4 4x4 89 99 03 401 | eBay

 

I've tried removing fuel cap when condition is present which made no change, I'm guessing this rules out a restricted tank vent? I will check atmosphere vents as well as compression and see where we are at. As far as fuel valve i just replaced it about a week ago due to leaking. I forgot to mention that it seems to just barely trickle in either the on or reserve position. I'm not sure how much flow it should have I will compare it to one of my known good bikes. I also replaced fuel line between fuel valve and carb thinking possibly it was restricted or collapsing, no help.

 

Should be a good flow from that new valve. Make sure the tank is clean.Open the valve,hit the hose with an air nozzle and and recheck flow again. Again not a bad a idea to just check compression to be on the safe side,order the carb kit and go from there. One step at a time.

 

OK so I think I found the issue, only about 80 psi of compression. This is the second top end rebuild that has gone south on me 1 on my 300 and then this one. I"m not sure what i'm doing wrong, I clean cylinder with soapy water after i get it back from machine shop then coat cylinder walls and piston with two stroke oil. Also I run 24.1 with oil pump disabled during break in.Sorry to complain just had to vent...LOL. Anyway back on topic is it possible to do a cylinder leakage test on these if so do I need to regulate air pressure way down? Also I know this has been discussed before but can someone refresh my memory on testing lower crank seal for leaking. Thanks again!

 

80 isn't good. First off have you been checking piston to cylinder clearance when you get the cylinder back? Some places bore too large to begin with. Plus you can usually tell on the piston. Seizure on exhaust side is usually from heat,air leaks,seals leaking,etc. Intake side seizures are usually from lean jetting. Plus 24/1 is WAY too rich. 40/1 is plenty enough premixing on these old low compression engines if you use good synthetic oil. 36/1 is max I'd go. Again piston to cylinder clearance shouldn't be more than .002 on these engines. Look at the manual and it shows it can even be less. Easier to just go ahead and replace the seals since you're going to have to tear it back down. Plus always check the bottom end. Pieces of lower rod bearing can take out a new piston if it reaches the cylinder. I've seen this happen time after time when people just rebuild top ends only. Several videos on youtube on leak down tests.

 

I have not personally been checking piston to cylinder clearance, I was assuming the machine shop did because i bought piston from them and it was always opened when i recieved it. Could the fuel mixture being to rich cause this problem? I have been checking my rod and bearings for up and down play and do not have any. I think I may start using Ritter Racing he seems to have a good reputation hopefully I can have some better results....

 

Use Rick Ritter. He knows his stuff.. Too rich an oil mixture can cause loss of octane needed for good combustion and can cause more bad than good. Can actually cause engines to run hotter in many cases. Seemed kinda strange to me but this was from Malcolm Smith when he came to the shop years ago and we had a chance to talk about oils. And I'm not one to argue with this guy. Basically the oil pump itself is metered from the factory at 50/1 ratio. That's why I always went 40/1 just to be on the safe side on telling people that premixed.Plus use a good synthetic oil. On new machines straight out of the crate we always mixed what the setup instructions called for and that was to mix at least a couple gallons 50/1 along with the oil pump only for break in purposes. That was in case any trapped air was in the oil lines.