So I have two problems with my 2004 XT225 I wanted some advice on. This is my first carb’d anything so not really sure how to deal with it. Basically the bike runs pretty good even though it’s pretty slow, however I live in Colorado and one of the trails I go on is about 10k feet or higher. The problem is when I hit certain hieghts it starts sputtering a little and once in higher trails if I stop the bike won’t idle and dies.

I also heard you should clean the air filter and the carb but is there any good resources on this?

Also any jets you would recommend because I’m very new to all of this and would prefer to end the sputtering and dying on the mountain.

The second issue is I have some sort of oil leak and I can’t find out where it’s beginning. I haven’t noticed any puddles on the ground but honestly didn’t think to look. Granted under the engine it looks fresh and coated. I did take the bash plate off a while ago and had cleaned off caked on oil before.

I did read if you overfill the bike it can leak so I’m thinking maybe that’s part of it but I don’t see any major loss of oil.

Internet diagnostics is really hard but based on your description it sounds like your bogging at elevation is likely due to a rich air fuel mixture. You either need less fuel or more air to bring things in balance. The amount of jetting decrease to reduce fuel will depend on what you have now. Stock the carb has a 125 main. I would open the carb and see if it is still stock or if someone already changed the jetting. Then go down one size jet and test. Wash, rinse, repeat until you get it dialed in. The other option is to get more air to the engine by drilling holes in the air box. I don’t like doing that because it is a permanent mod that can’t be reversed.

The common oil leaks are the o-rings that seal the starter motor or the o-rings under the two valve covers. Yamaha sells the o-rings but you should be able to source them at your neighborhood Ace Hardware. Bring the old o-rings to Ace and match them up exactly. Max price is no more than $1/o-ring.

Good luck.

The elevation problem is likely mixture, the usual solution is more air. The quick way to confirm that is to remove the air filter cover when it starts to misbehave and see if the additional air helps it run better.

The more permanent solutions are to remove the snorkel from the air box and/or cutting a hole or two in it to let more air in. There's various solutions to making this reversible with plugs or sliding doors you can install. You can supplement that by doing the Z1 mod to the exhaust or getting an aftermarket pipe. Note that all of those will make the bike louder to varying degrees.

This thread has some details though the pictures may not work anymore. Sometimes google will find the pictures.
http://www.xt225.com/forums/ubbthreads.php?ubb=showflat&Number=135150&page=1

http://www.xt225.com/forums/ubbthreads.php?ubb=showflat&Number=7448&page=1


The alternative to more air is less fuel. The bike should have a #40 pilot jet and a #125 main jet if it's stock. I would start by reducing the main jet 1 size to 122.5 and go from there.


The oil leak... The usual suspects are the o-ring at the nose of the starter, the valve covers, the output shaft seal, the shifter seal, and the gasket between the base of the cylinder and the crankcase.

When my starter o-ring failed, it failed big. It wasn't a slow ooze, it was like a leaky faucet. There was oil everywhere by the time I got home. Thankfully, that's an easy one to fix. Just be careful with the starter bolts, they're pretty long and thin.

The valve cover o-rings are also easy to fix. If it's leaking there, you'd likely smell the burned oil and see it on the cylinder.

The output shaft and shifter seals are usually fairly obvious as well due to their location.

The cylinder/crankcase gasket is the usual "I can't find it" leak and a lot of work to fix. You've got to remove the engine to replace that gasket. Mine has had a slow leak there for years. I just wipe it off occasionally so it doesn't drip in my garage and keep an eye on the oil level. Some folks have had temporary success running a bead of RTV around the base of the cylinder to try to slow down the leak, but replacing the gasket is the only way to stop it.

A simple way to confirm the source is to remove the bash plate and clean it really thoroughly. Then dust the engine with flour or baby powder and let it run for a little while. The white powder will highlight where the oil is coming from.

Poor performance above 10,000 feet is what I would expect for a carbureted engine. As Peejman suggests, a smaller main jet is the place to start. When mucking about with carburetion, make one change at a time.