Posts
1491
Joined
7/23/2013
Location
Farmville, NC
US
Fantasy
1936th
Edited Date/Time
8/17/2019 3:56am
I bought my son a 2015 YZ250F in August of 2014. At 12 hours the bike started cutting out, snapping and popping, barely running. At first you could shut it down and restart it 15-20 times and it would clear up. It progressively got worse until eventually at round 20hrs it shut down and wouldn't start. Bike now has 55+hrs on it and probably 10+hours of that has been spent riding the bike around at a shop or just running trying to figure out what's wrong.
First Yamaha tech that worked on it at the Hog Haven Pro Shoot out last year, said it was a "fuel pump." Yes, that was the first big race we missed due to the bike. Put a NEW fuel pump, 20 mins later same problem. Bike has been to at least 2 different Yamaha dealers, most main electrical parts and has been swapped out. Even a new computer. Bike ran decent for about 8hrs until it would get wet on the track. My son has hit the same mud hole several times on a particular track and the bike would immediately shut down. Let it dry out and would crank, MOST of the time.... Not the spark plug cap problem either.
Just got the bike back from the shop after having a new top end installed. They supposedly replaced two sensors, finally it was running good. 1.20 hours later it is doing the same thing.
I ordered the same two new sensors from Rocky Mountain ATV a few days ago and had them overnighted. Installed new temp sensor and pressure sensor. Bike fired right up ran like a charm. 1.3 hrs later, bike has shut down again and would not crank.
Went to the track bike ran fine for a few laps. Bike shut off in mid air on my son TWICE. Even tired installing new kill switch, as a fellow YZ owner had the same problem and it seemed to cure his. Put it on and the bike ran great for just a few laps and shut off again. As of right now it will not crank. I can probably go to it tomorrow and it will run, for a few laps anyway....
I am at my wits end. I have tried not to post, hoping Yamaha would find the problem. After a ton of money thrown at a bike that hasn't ran right since 12 hours I have had it.
I know of at least 4 different 2015 YZ250F's that have had similar issues. No ways as bad as ours. We were at a small local race and there where 3 new YZF's were having the same issues at the same time. One had 2.2 hours on it... All of the others have cleared up without a repeat occurances as far as I know.
I can't help but think others are having problems and are just as lost as us.
Again we had a big race this weekend and my sons NEW bike wouldn't not run dependably... We have only had this bike make it through a few races. He wanted to make a run at Loretta's this year. Haven't had the bike running right long enough to try to qualify. It is really sad when you can't depend on a BRAND NEW BIKE and you see your sons heart broken race after race....
First Yamaha tech that worked on it at the Hog Haven Pro Shoot out last year, said it was a "fuel pump." Yes, that was the first big race we missed due to the bike. Put a NEW fuel pump, 20 mins later same problem. Bike has been to at least 2 different Yamaha dealers, most main electrical parts and has been swapped out. Even a new computer. Bike ran decent for about 8hrs until it would get wet on the track. My son has hit the same mud hole several times on a particular track and the bike would immediately shut down. Let it dry out and would crank, MOST of the time.... Not the spark plug cap problem either.
Just got the bike back from the shop after having a new top end installed. They supposedly replaced two sensors, finally it was running good. 1.20 hours later it is doing the same thing.
I ordered the same two new sensors from Rocky Mountain ATV a few days ago and had them overnighted. Installed new temp sensor and pressure sensor. Bike fired right up ran like a charm. 1.3 hrs later, bike has shut down again and would not crank.
Went to the track bike ran fine for a few laps. Bike shut off in mid air on my son TWICE. Even tired installing new kill switch, as a fellow YZ owner had the same problem and it seemed to cure his. Put it on and the bike ran great for just a few laps and shut off again. As of right now it will not crank. I can probably go to it tomorrow and it will run, for a few laps anyway....
I am at my wits end. I have tried not to post, hoping Yamaha would find the problem. After a ton of money thrown at a bike that hasn't ran right since 12 hours I have had it.
I know of at least 4 different 2015 YZ250F's that have had similar issues. No ways as bad as ours. We were at a small local race and there where 3 new YZF's were having the same issues at the same time. One had 2.2 hours on it... All of the others have cleared up without a repeat occurances as far as I know.
I can't help but think others are having problems and are just as lost as us.
Again we had a big race this weekend and my sons NEW bike wouldn't not run dependably... We have only had this bike make it through a few races. He wanted to make a run at Loretta's this year. Haven't had the bike running right long enough to try to qualify. It is really sad when you can't depend on a BRAND NEW BIKE and you see your sons heart broken race after race....
I think you should get a new bike, at least here in Finland you would be able to get one from the importer if you have such massive problems with a new bike.
Fuel starvation....Plugged fuel tank vent in the cap.
Vapor locking.....Put insulation under the fuel tank.
Coil breaking down due to heat.
Paw Paw
If the bike is running good and you hose the bike down with water will it bring the prob on immediately?
Another issue my neighbor has had was running MR12 in his 250f and now 450. I think it is a vapor lock issue running oxy fuel here in this heat. He ran pump gas and the bogging issue quit, VP also told him to try this to confirm. Like Paw Paw mentioned heat blanket under tank couldn't hurt either.
The Shop
Jakes Dad, that blows my mind that you would have to pull a harness to wash a dirtbike. Appreciate the info! I have been washing bikes with pressure for almost 30 years. Other than a seal or two I have never had a problem. If the bike can't stand water something is wrong. I bet you want see one of the Star Racing Yamaha's quit during a mud race this year at the Nationals. While my sons bike, prepped as they suggest, want make it 3 laps in the mud.........
The stator and pump have supposedly been replaced by Yamaha. I helped install the pump so I KNOW it was done.
The connections have been coated in d grease several times already.
Far as fuel I use high quality 93 octane that is no more than 5 days old. This thread is the first I have heard of vapor lock being an issue. I really don't feel this is the problem though. It seems to be an electrical issue.
Right on schedule I just went out and kicked the bike, 3rd kick it fired up and ran great. I am sure I could him on it for any where from 2 laps to about an hour and a half before the will die for the day....
Calling Yamaha when they open!
Paw Paw
I suspect a bad connection or short somewhere or some other electrical problem like a bad coil. I would be inspecting every millimeter of that wiring harness as a first step.
Good luck.
Paw Paw
Far as vapor lock, would removing the cap to check the fuel level correct that? Point being, it still does no matter fuel level or after checking level.
Good luck
What you describe is failure to vent. If air can't get in the top, fuel can't get out the bottom because it's trapped by vacuum. Like when you hold your finger on top of a straw full of soda.
Vapor lock is when heat from the engine raises the temp of the underside of the tank, pump, and high pressure line to the injector to the point that the fuel boils. You then have air bubbles being delivered to the injector instead of a nice solid stream of fuel, causing momentary cutting out. This is why PawPaw suggested insulation under the tank and you see the Pros running the foil insulation under there.
I would assume that as soon as the fuel cools off it should go back to running normally, would I be correct?
If this is the case, I don't think this is our problem. Bike has sat for days with the same problem. It normally clears up after a few hours but no always.
Anyone have pics of the insulation on the bottom of the tanks? I would like to see exactly how to CORRECTLY do it.
http://motocrossactionmag.com/uncategorized/mxa-product-test-cv4-heat-shield-mat
Pit Row
Does this really help the bikes performance or more of a preventitive mod?
Hoping the new harness will be here today and by this weekend I will know whats going on. Got another big race this weekend. Hopefully we can keep him on the 250F! He rides schoolboy 1 on a YZ125 as well. Thank goodness we kept that bike or we would have missed most races since buying the 4stroke.... He managed to get 3rd overall in our fall series in 250C riding his 125 most of the races as the 250F wouldn't run right....
Don't know if it is normal but the stator side of the motor was scorching hot!! We thought the coolant must be low. I immediately popped the rad cap and it was properly filled and was cool enough to hold the cap. The other side was no ways as hot. SO we ordered ANOTHER stator right there on the spot, supposed to be here Tuesday.
My son wants to run a LLQ this weekend and I don't think the bike will make it Had to ride the old two stroke yesterday! Good thing I picked up a decent YZ250 smoker or we would be in bad shape. Blowed the fork seals out of that yesterday so tearing it down to send off.... It never ends LOL!
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