15 YZ250FX - "Blubber"

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.

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Monk
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1/31/2017 6:58am
I would bank on a dirty fuel filter. I had a similar issue but I had 100+hrs on the bike at the time... You can pretty much idle around but as soon as you get on the throttle it's bogs down.

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...
1/31/2017 9:49am
Thanks Monk. The fuel filter does follow my logic as well. Being as intermittent it is and running perfect most of the time I don't think it's a hard failure of anything.

I did not know that the bike had an internal hour meter. I'll have to pick up the tuner for it.
2/15/2017 1:36pm
Update so far (2/15): While having the valves checked I also had the mechanic change the injector. This was the cheapest logical possibility so I started there. He pulled the old one off and didn't see any cracks or cuts in the o-ring so no obvious defect.

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.
ianhendry46
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Murfreesboro, TN US
2/15/2017 9:52pm
I have two 2017 yz250fs that I pulled the tanks off of tonight, and neither ran fuel continuously.

The Shop

2/16/2017 5:35am
I have two 2017 yz250fs that I pulled the tanks off of tonight, and neither ran fuel continuously.
Thank you for the confirmation. I'm a bit surprised if this is the issue causing the bike's intermittent "blubbering", backfiring and stalling. I'd figure that would be a lean condition and not rich. Regardless, it's not the proper operation of the pump so it'll get replaced.
ianhendry46
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Murfreesboro, TN US
2/16/2017 8:55am
What does the spark plug look like?
2/16/2017 8:56am
What does the spark plug look like?
Brand new now. Figured just change it out since the valves are being checked.
mattyhamz2
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2/16/2017 9:27am
I haven't seen a fuel injected bike continue to dump fuel once the fuel line is removed from the pump. Every one I have seen has trickled then stopped within a few seconds. Hope its a cheap easy fix for you
2/16/2017 10:56am
The leak down test was good, but the valves were way out of spec being very loose.

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.
3/6/2017 7:45am
Well, I changed the pump this past week and took advantage of the nice weather this weekend and did a bit of riding. After 3 hours it had no issues with its "blubber". I'm really hoping the pump was the root cause and it won't resurface.

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.
Skerby
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Mayes County, OK US
3/6/2017 4:15pm
The valves were loose? That's wild, I figured they always tightened up on the adjustment side of things.
3/6/2017 4:19pm
Skerby wrote:
The valves were loose? That's wild, I figured they always tightened up on the adjustment side of things.
They were so loose the only explanation i could come up with was that whoever adjusted them the last time really didn't know what they were doing.

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.
DuroTools
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Middletown, CT US
2/16/2020 10:35pm
I know this is super old but hey MyersAvionics did the pump fix your issue. I am having similar issue.
2/19/2020 6:27am
DuroTools wrote:
I know this is super old but hey MyersAvionics did the pump fix your issue. I am having similar issue.
This is quite old! I've had two bikes since this YZ. The pump was not the issue. There was a poor connection and whenever I'd land from a hard jump it would partially disconnect and the bike would have issues.

Cleaned up all of the electrical and it worked fine after.
DuroTools
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Middletown, CT US
2/20/2020 6:32pm
DuroTools wrote:
I know this is super old but hey MyersAvionics did the pump fix your issue. I am having similar issue.
This is quite old! I've had two bikes since this YZ. The pump was not the issue. There was a poor connection and whenever I'd land...
This is quite old! I've had two bikes since this YZ. The pump was not the issue. There was a poor connection and whenever I'd land from a hard jump it would partially disconnect and the bike would have issues.

Cleaned up all of the electrical and it worked fine after.
Thanks for the reply! I think I got mine fixed as well by redoing all the connections and also swapped the water temp sensor. Not sure which fixed it but for now it's running ok so that's all that matters!
Tuna
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CA
2/21/2020 4:10am
DuroTools wrote:
I know this is super old but hey MyersAvionics did the pump fix your issue. I am having similar issue.
This is quite old! I've had two bikes since this YZ. The pump was not the issue. There was a poor connection and whenever I'd land...
This is quite old! I've had two bikes since this YZ. The pump was not the issue. There was a poor connection and whenever I'd land from a hard jump it would partially disconnect and the bike would have issues.

Cleaned up all of the electrical and it worked fine after.
DuroTools wrote:
Thanks for the reply! I think I got mine fixed as well by redoing all the connections and also swapped the water temp sensor. Not sure...
Thanks for the reply! I think I got mine fixed as well by redoing all the connections and also swapped the water temp sensor. Not sure which fixed it but for now it's running ok so that's all that matters!
What did you do with the water temp sensor?

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