Ok, here is the situation. I have a 97 Trail Boss 250 that has been running good for me all year. I drove alot of miles on gravel roads this weekend and towards the end I noticed that my top speed was down a mph or two. I contributed this to a dirty air filter from all of the dust on the gravel roads. After a 25 mile ride the engine died as I came to a stop. There was no unusual noise or feeling, just like it ran out of gas. I could not get the engine started again until I messed with the idle speed screw. Figured that maybe the vibrations caused it to loose its adjustment. I rode the 25 miles back without a problem other than the mph or two off the top speed. Tried to start it the next morning with negative results. Pulled the plug after several minutes of cranking and it was dry, shouldn't it have been wet? I then checked to see if there was fuel coming out of the overflow on the carb like it has since I bought it. No fuel coming out at all. In the past I have always had to manually turn the gas switch off to avoid the fuel leak. I came to the conclusion that the engine was not getting fuel and that it was time to remove the carb to clean and rebuild it. When I removed it I found the boot that connects the air box to the carb was torn. I assume that dust/sand from the gravel roads was sucked into the carb through this tear and it clogged it up. My concern is that if enough dust/sand was sucked into the carb to clog it that I may have some major engine damage now. I have the carb with me but the rest of the machine is 200 miles away so I cannot check the compression right now. Sorry for the lengthy post but does anybody have any ideas. I hope its just the carb because the leak being gone and the spark plug being dry has me thinking that way. With the carb removed gas flows freely out of the supply line so I know that the fuel is getting to the carb.

 

im gonna say that you are gonna atleast need new rings. and it might have caused more damage with the tear because it creates a lean condition. very bad on a 2 stroke (bad on 4 stroke too but can get away with it for a bit). your going to need a compression test and/or a leakdown test.

 

The odd thing is that even just before I shut it down I had very good throttle response on the trails and didn't notice any lack of performance other than the top end speed being off a mph or two. If the engine was damaged shouldn't I have had a problem accelerating? If I need rings wouldn't this be the time to just get the cylinder bored and order a new piston?

 

you really need to take a look at the cylinder to see how many scratches are on them form the dust/dirt if any got sucked in. the first thing you should do no matter what is a compression test when you get back to the bike w/a clean carb. was the filter extremly dirty? i've seen them shut right down and wouldnt start or run because of a clogged air filter(2 stroke 300) you might be lucky and just have a dirty carb/filter. buy a new carb boot for sure and check it out after you put the carb back on. cant really do any more harm trying to start it and if it runs then your saved. imo

 

Does anybody happen to have any extra boots? I have looked on Ebay for boots to fit on each side of the carb with negative results. Dealer is to costly.

 

You really need to do a compression check on the engine to see if the compression is low. The engine will seem to be running extremely well when it's running lean. If you need new rings, a new piston would be a good idea as well.

 

Well I rebuilt the carb and replaced both of the air boots. New spark plug and air filter also.

Good News: I seem to have gotten rid of the fuel overflow problem I was having and once I got the engine started i was able to adjust the carb and get it running pretty good.

Bad News: The only way to start the engine was to pour a small amount of oil through the spark plug hole onto the cylinder to get enough compression for it to go.

I brought it home to work on it this fall. I ordered a Wiseco piston with a cylinder to match it. My old one will be returned for a core refund. Tonight I took the engine apart and to my surprise the cylinder walls did not appear to be that bad and the piston rings were not broken into pieces. The piston skirt was also still intact. The skirt did have some pretty good gouges where the intake and exhaust ports were at. I am expecting the parts early next week and I'm very excited to get this thing back in good running shape. I do have a question about the oil line from the pump to the cylinder. I'm going to replace it while everything is apart. Do I have to purchase any particular type of hose/tubing or will anything work? Also the foam padding on top of the gas tank is pretty trashed, is this worth replacing or not? Any other suggestions on what to look for or what to replace while I have everything apart? Thanks

 

I also found that the inside of the gas tank had some flakes of stuff in it. I will be washing it out. There are screens on the fuel intakes but has anyone added an inline fuel filter? And again any ideas on the oil hose/tube and the foam padding?

 

Update: I installed the new piston and I'm hoping to finish putting everything back together tonight. I am replacing the stock 145 main jet with a 160 in hopes that the motor will run a bit cooler on the long road rides with substained high rpm's. Does anybody have experience with the larger jet on a stock bike, I'm a bit concerned that it may be a little to rich?

 

I put a cheap clear plastic in line filter on mine and I guess it's working. Hasn't clogged up, but haven't pulled the carb apart to see if anything is in it since it's run fine. Just cheap insurance.

Seems like the foam is more for anti rattle to me. If nothing else, you could go by an upholstery shop and see if they have a chunk of foam you could replace it with.