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Yamaha Dirt Bike Fuel Tank Question


TOXXIC

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We have a 2001 Yamaha XT225, which recently developed a fuel leak. Initially, I assumed it was at the petcock as the fuel was dripping down the left side of the motor (clutch lever side) and pooling on the floor.

However, after pulling the side cover I saw a small drip of fuel above the petcock on the side of the fuel tank. This concerned me as I thought there might be a pin hole size leak someplace in the tank.

This is where it gets wierd. The top of the gas cap is wet with fuel, and my son mentioned the key has gas on it when you pull it out of the locking cap. Sure enough, when I pulled the key out of the locking gas cap the bottom 1/4" of the key is wet with gas.

I havent' dug into this yet nor pulled the tank to investigate. I considered it may have been overfilled and venting out, but the fuel level is considerably lower than the filler neck.

These bikes have been fun for the kids as they are pretty bullet proof, electric start, and fun to ride. However, they sure are tempermental with cold starts after several weeks of inactivity. I am guessing the parts in the carbs are tiny and get ocluded rather easily.

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If any carb'd bike sits for more than a week or two without being started up, you are going to get a buildup of deposits in the jets, clogging them up.

After a ride just turn the fuel off and run the engine dry of fuel then store.

A carb clean generally runs $150.00 here in So Florida!

Edited by John01XX
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Thank goodness it doesn't do what the old Honda 350's did. I'm guessing I bored and installed new pistons in 150 of those. If the petcock was not shut off, often the carb floats would stick and drain the tank into the oil. Not many miles into the next ride the pistons would seize. Kept me very busy for a few years

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I am guessing the parts in the carbs are tiny and get ocluded rather easily.

While that is true, it takes a while. I have a Honda generator that sits for months without being started. I should start it once a month but I forget. I have had it about ten years and this was the first year that I had to clean the carb and it is a tiny carb. I do keep some Sta Bil and a little Sea Foam in it. Also, my two bikes sit from November to April or May every year.

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I've found that some carbs will gum up easily and others won't without a lot of reason that I can think of, but running it dry or draining is a good idea. As for the gas everywhere I think you need a fresh start and see for yourself what's happening. Maybe they overfilled it before you got to it, just bouncing it hard, fell over and ain't tellin... The tank can be patched, most parts stores sell a gas tank repair kit; it's just epoxy and some matting to cover large holes.

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We have a 2001 Yamaha XT225, which recently developed a fuel leak. Initially, I assumed it was at the petcock as the fuel was dripping down the left side of the motor (clutch lever side) and pooling on the floor.

However, after pulling the side cover I saw a small drip of fuel above the petcock on the side of the fuel tank. This concerned me as I thought there might be a pin hole size leak someplace in the tank.

This is where it gets wierd. The top of the gas cap is wet with fuel, and my son mentioned the key has gas on it when you pull it out of the locking cap. Sure enough, when I pulled the key out of the locking gas cap the bottom 1/4" of the key is wet with gas.

I havent' dug into this yet nor pulled the tank to investigate. I considered it may have been overfilled and venting out, but the fuel level is considerably lower than the filler neck.

Ok, I'm not hands on familiar with this bike so.... question? Metal tank ?With locking gas cap I'm speculating the answer is, Yes. Also with Locking gas cap and metal tank, I am speculating 2 seals, and an inner metal vent tube, that is under the cap, and vents out the bottom of the tank. Yes/No?

My guess is said tube is plugged, and since the fuel vapors can't get out through the tube, they are coming out through the key hole in the cap, and since the cap is metal an colder, it condensing inside the gas cap, hence fuel on the Key.

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Some good thoughts so far in this thread. I hadn't thought of the fact one of my sons could have tipped the bike over as there was no visible damage. But my Jeep has a flat tire on the sudden and I haven't driven it in weeks.

As to the make up of the tank it is metal with a metal gas cap. I took it off yesterday and shook it looking for pin hole leaks but could not find any. When placed nearly upside down gas began to rush out from under the gas cap. Inspection of the inside of the gas cap revealed a large amount of dirt and residue build up on the rubber gasket. I cleaned that thoroughly and reinstalled the tank. However, now that you mention it, I didn't see a vent hose or line. Just the tank and the fuel petcock assembly. However, your theory of a plugged vent tube and pressuring the fuel vapors out the key hole of the gas cap does make sense.


Here is a link to a schematic of the fuel supply system.

http://www.boats.net/parts/search/Yamaha/Motorcycle/2001/XT225%20-%20XT225N/FUEL%20TANK/parts.html

http://cdn.boats.net/diagram/yamaha/MCY/2001/XT225N_NC/IMAGES/FUEL_TANK.png

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After cleaning cap, taking the tank off and inspecting the tank for leaks I am more perplexed. The fuel appears to be leaking down the from the underside of the tank, and causing a tiny pool to form on the left side of the engine case.

To test Eric's venting theory I am going to leave the gas cap off overnight with a rag stuffed in the top. Should still vent a bit, and not be a captured system. Now I am starting to suspect a pin hole leak.....

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Might be easiest to leave tgetank off the bike for a day or so resting on a clean sheet of cardboard. If thetank and card was clean to start off it should give a clear indication of where the leak lives. On the bike it's gonnabe way harder to trace.

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Those metal caps are the venting system. I have never had issue with one. Give it a good blast with some carb and choke cleaner.

Turn the fuel off and see if it still happens. Maybe go so far as to disconnect the fuel line to the carb and drain the carb as well. Good time to clean it too.

Many older carbs have the floats stick and drain the contents....but sounds like you may have eliminated that as an issue.

For the cooler months and hard starts...have you dropped the clip in the main pilot needle to richen it up a bit?

Edited by TuffguyF4i
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Those metal caps are the venting system. I have never had issue with one. Give it a good blast with some carb and choke cleaner.

Turn the fuel off and see if it still happens. Maybe go so far as to disconnect the fuel line to the carb and drain the carb as well. Good time to clean it too.

Many older carbs have the floats stick and drain the contents....but sounds like you may have eliminated that as an issue.

For the cooler months and hard starts...have you dropped the clip in the main pilot needle to richen it up a bit?

I did not drop the clip in the main pilot needle, but can see how that would be a great idea! I solved the problem with the leaking tank, I sold the bike last night! :D I have a second 2001 XT225 at my cabin, which is cold blooded and would benefit from the main pilot needle adjustment.

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