Maybe a dumb question, but Im stumped!!!

As the title states, Im stumped. Took my freshly rebuilt Yz 250


out to the track saturday filled it up with fresh mix 50/50 pump/race fuel and Amsoil Dominator mixed at 40:1 and put in a good 30 mins of track time. Took a 30 min break and went back out and ran out of fuel after 5 mins. Thats way too fast, seeing as I took my 08 yz250 to get a couple laps in on the race bike as well and let my buddy ride my 03 yz 250 and got two full 30 min runs out of both of them on the stock tanks with the same premix. Pretty much stock motor other than port and polish, and squish set which is also done on all 3 bikes. Ive went over carb settings 3 times and everything is well within spec. Theres no fuel leaking from the over flow and plug chops show my jetting to be a tad lean on the main but nothing that cant be cured by goin up one step.

Im no pro so theres no way Im pushing the bike that hard to run that much fuel through the bike in an hour. Anyone have any ideas?:thumbsup:

You're either crazy fast or there's a problem. I normally average about a gallon every hour or so.

I doubt the bike would run well at all, if it was actually drinking that much fuel.

It has to be leaking from somewhere, carb or tank vent line.

Maybe the vibrations from the engine are causing the float needle to not seat and therefore dumping gas.

Maybe try putting your carb lines into a water bottle and zip tying it somewhere creative.

Nice bike btw.

GMO has a point there.

My 07 yz250 leaked fuel. Then when i got to the top of my yard before i hit the trails i smelled gas, so all i did was take the carb apart and give it a nice clean. Especially the float. Also check the float needle, theres like nilon tip that actually creates a seal and it may not be sealing properly. But as of right now im thinking the float is stuck.


Your just a really fast wide open rider

Carb was just rebuilt, and float is within spec and it would dump fuel any time the fuel was on if the float was stuck. Not only if the bike is running. Ive even left the fuel on overnight in the garage and there was no fuel on the ground or any smell what so ever. Also filled the tank right to the top of the hump in the tank so I could visibly see if any fuel had leaked out and nothing. Still at the exact same level.

I do rev the piss out of it and weigh 230 lbs before gear. But theres no way this motor is that far off than my 03 which I can get in two 30 min rides on the track and still have about 1/3 of a tank left. I cant even get a 40 min ride out of this thing.

I agree Im losing fuel somewhere because I know there no way its getting burnt, I just cant figure out where. Ive heard two strokes will suck down fuel if they are jetted too rich but Im actually a little lean, which doesnt make much sense.

The fuel has to be coming out the vent, jets don't flow that much.

BTW, your bike looks strikingly similar to mine!

I fitted a brand new float needle once and had the same problem. The float hight was spot on and if the bike sat on the stand with the fuel on it would drop no fuel, but as soon as I rode it fuel spewed out of the overflow. What i found was the spring in the needle was heaps weaker than the original. I put the original one back in and had no problems since. If you want to see what vent it is leaking from zip tie a small bag on to the hose and ride the bike.

Check if your powervalve is correctly assembled. I rode my YZ250 several times without a powervalve (since it was backordered for almost a year, and nothing showed up on ebay) and at the time I noticed how much substantially more fuel the bike used.

PV is installed correctly... Im 100% positive on that, the bike screams up top.

Edit... Ill look into the spring.

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