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1/31/2017 5:48am
1/31/2017 5:48am
I'm curious to know the general opinions on here on an odd issue on a used bike i recently purchased. It's a 2015 YZ250FX. Supposedly had 30hrs on it when I bought it, but it never had an hour meter and also had the valves checked approximately 10hrs ago, including the 4 I've put on the bike. I race against the guy I bought it from and he has a good reputation so I don't think he'd deliberately fib on the numbers.
Description of the issue:
The bike runs great for the most part. I've only installed a Rekluse as I'm not a fan of the cable clutch feel after having a hydraulic for quite some time. Just recently, I noticed it will "burble", backfire and quit on me. It's done it twice now recently. The first time, I rode it back to the truck, looked it over and didn't see anything obviously wrong. After letting it sit for approximately 5 minutes, I started it back up to see if it would be a new constant issue. I rode it the remainder of the day without incident. I thought It must have been a fluke.
More recently, I rode an endurocross this weekend. The bike worked great in practice and qualifying, but in the main, it started to do the same thing after about half the race. It will only do this when you try to get on the gas. It was able to finish the race, but I had to really take it easy and not turn the throttle hard.
To say the least, it's very intermittent and difficult to reproduce. I think it may be something to do with the fuel system (injector or pump?), but I'm not a 4-stroke mechanic.
I'm looking for any type of ideas or backgrounds that have had similar issues. I'll be taking it to a mechanic regardless to be worked and fixed. While fixing this, I'll have them also check the valves and all other wear items as well. Just a bit too busy to dig into it with work and MBA fun stuff.
Description of the issue:
The bike runs great for the most part. I've only installed a Rekluse as I'm not a fan of the cable clutch feel after having a hydraulic for quite some time. Just recently, I noticed it will "burble", backfire and quit on me. It's done it twice now recently. The first time, I rode it back to the truck, looked it over and didn't see anything obviously wrong. After letting it sit for approximately 5 minutes, I started it back up to see if it would be a new constant issue. I rode it the remainder of the day without incident. I thought It must have been a fluke.
More recently, I rode an endurocross this weekend. The bike worked great in practice and qualifying, but in the main, it started to do the same thing after about half the race. It will only do this when you try to get on the gas. It was able to finish the race, but I had to really take it easy and not turn the throttle hard.
To say the least, it's very intermittent and difficult to reproduce. I think it may be something to do with the fuel system (injector or pump?), but I'm not a 4-stroke mechanic.
I'm looking for any type of ideas or backgrounds that have had similar issues. I'll be taking it to a mechanic regardless to be worked and fixed. While fixing this, I'll have them also check the valves and all other wear items as well. Just a bit too busy to dig into it with work and MBA fun stuff.
Before you go about pulling the pump, check the spark plug/spark plug cap making sure it seated properly. Check all electrical connections and while at it put some di-electric grease in all of them. Check to make sure the fuel line isn't being pinched off by the tank or such. Check airfilter and make sure there are no obstructions...
And, it's much easier to hook up a tuner and play with some mapping. It's 'could' be running rich but I doubt that's the issue. During that time you could also check total hours as the YZF(x) models have built in hour meters...
I did not know that the bike had an internal hour meter. I'll have to pick up the tuner for it.
That said, the bike did provide an additional clue when pulling the tank off. When disconnecting the line to the pump, it ran gas continually through the pump. With my old bike, it would trickle a bit out, but that would be it and it would stop. With this, it was a steady slow stream out of the pump. Eventually, the mechanic had to just plug it up to get it to stop.
This is not normal for late model (2015) YZ250F (FX)'s is it? Note that it has an enlarged tank on it (3 gallons) so there is more pressure being applied.
I'm leaning toward buying a new pump and trying that out as I don't think the current behavior is standard.
The Shop
Fixing the valves first and testing. Need to reduce variables to determine the root cause. Going to test it out this Sunday after getting home from the SX.
I'd be interested in seeing an exploded view of the pump. I'm guessing it's an electronically driven solenoid to regulate fuel flow to the injector. Maybe it had gotten a bit dirty or gunked up from something and was sticking in an on or off position. That would be telling why the pump was spilling gas continuously when we first took it off to check/adjust the valves.
First race is the 26th of this month so fingers crossed it'll be good to go.
I'm really surprised the bike still ran as good as it did with the valves like that. After the first race I'm going to check them again just for peace of mind.
Cleaned up all of the electrical and it worked fine after.
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