Power drop/block during acceleration

I picked up my very first WR250X about a week ago and the first thing I noticed was the power drop/block during low end acceleration.
The bike was stored with some fuel in there for almost a year. I am thinking maybe its the old fuel that's doing it but I am unsure. I am in the process of eliminating the trouble maker by burning out the fuel so I can fill it up with good stuff, doing an oil change and filter change this weekend and possibly a spark plug change as well.
I've read something along the lines of fuel system or gas line being a known issue with the earlier models but the single owner who owned it before me had no issues so I am leaning towards the fact that its probably not that.
Any suggestions or ideas where or what I should be looking?

Take the gas out and just put in some good 91 octane, best and easiest place to start, did the other owner get the stator replaced, make sure that gets done, free recall. the dealer just check`s the VIN number and can tell. good luck.

What do you mean by a block or cut? Is it a quick stumble? Does it happen all the time? Reason I ask is I know on my 2015 which is basically all stock motor wise, I do notice a lean "stumble" as the bike is warming up. It occurs around 1/4 throttle. It goes away when the bike warms up. If you look at people who have EFI fuel controllers, its the setting where they add fuel (like the second setting) so it makes sense. If it happens all the time then something else is happening within the system. Possibly bad gas or fuel pump issues etc. Run some Seafoam through a tank of gas too.

Fiftygrit wrote:

Take the gas out and just put in some good 91 octane, best and easiest place to start, did the other owner get the stater replaced, make sure that gets done, free recall. the dealer just check`s the VIN number and can tell. good luck.

Will try the gas.

Did not know about the started recall, thanks for the heads up, will check with dealer.

CRFan1 wrote:

What do you mean by a block or cut?  Is it a quick stumble?  Does it happen all the time?  Reason I ask is I know on my 2015 which is basically all stock motor wise, I do notice a lean "stumble" as the bike is warming up.  It occurs around 1/4 throttle.  It goes away when the bike warms up.  If you look at people who have EFI fuel controllers, its the setting where they add fuel (like the second setting) so it makes sense.  If it happens all the time then something else is happening within the system.  Possibly bad gas or fuel pump issues etc.  Run some Seafoam through a tank of gas too.

That's right, its a quick stumble but it's always there during initial throttle.
Let me start with the gas and see how that goes and maybe seafoam.

Cheers!

CanadianWR250 wrote:

I picked up my very first WR250X about a week ago and the first thing I noticed was the power drop/block during low end acceleration.
The bike was stored with some fuel in there for almost a year. I am thinking maybe its the old fuel that's doing it but I am unsure. I am in the process of eliminating the trouble maker by burning out the fuel so I can fill it up with good stuff, doing an oil change and filter change this weekend and possibly a spark plug change as well.
I've read something along the lines of fuel system or gas line being a known issue with the earlier models but the single owner who owned it before me had no issues so I am leaning towards the fact that its probably not that.
Any suggestions or ideas where or what I should be looking?

I've ridden bikes for 40 years, and when I got my WR250 I killed it several times while taking off from a stop. It might just be the nature of the bike - this forum is full of solutions... My solution was to gear it down, substantially.

Mine runs badly off the bottom when the gas gets a couple months old but ok when revved up.

Fresh gas will likely fix it.

Gas may indeed help...the unfortunate fact is these bikes have a very lean off idle transition to meet emmissions. I can certainly feel it before the bike gets warmed up. Bumping the CO setting up a couple numbers may help outside of doing a fuel controller or PCV, etc.

CanadianWR250 wrote:

That's right, its a quick stumble but it's always there during initial throttle.
Let me start with the gas and see how that goes and maybe seafoam.

Cheers!

Mine does that when cold at partial throttle. It usually goes away when the bike warms up. Fresh gas, old gas, 93 octane or 87 octane, no difference. I did get a slight improvement when bumping up CO numbers when ambient temps are low. I have thought about trying a new spark plug (about 12k miles on the stock one).

dmmcd wrote:

CanadianWR250 wrote:

That's right, its a quick stumble but it's always there during initial throttle.
Let me start with the gas and see how that goes and maybe seafoam.

Cheers!

Mine does that when cold at partial throttle. It usually goes away when the bike warms up. Fresh gas, old gas, 93 octane or 87 octane, no difference. I did get a slight improvement when bumping up CO numbers when ambient temps are low. I have thought about trying a new spark plug (about 12k miles on the stock one).

Spark plug won't help that issue (my bike only has 1300 miles).....it is the lean fuel mapping in the ECU and it is done to meet emissions, etc. The only way to fix it would be via a PC5 or a fuel controller.

CRFan1 wrote:

Spark plug won't help that issue (my bike only has 1300 miles).....it is the lean fuel mapping in the ECU and it is done to meet emissions, etc.  The only way to fix it would be via a PC5 or a fuel controller.

Oh, I've got an FMF fuel controller, so it is not as refined as a PC5 with the ability to change low RPM off-idle fueling, but it helps a little. It is definitely worse when below 50 deg outside when bike is cold.

Interesting that you can't make that better with the FMF unit....have you tried changing settings, etc. (i think it would be the second setting)?

Rule of thumb is...Lean conditions tend to get better as the bike warms up and rich conditions tend to get worse as the bike warms up.

Turns out it was the old gas in there that was the culprit.
I had a lotta gas in there that I just didn't have the patience to burn it out and then fill up the tank with good fuel so I took apart the tank and emptied it into my Honda Element [hopefully that doesn't crap out] and filled 91 octane last night and it runs with no block/drop at all.
Thanks Guys!

Interesting to read about the fuelling issues some members have/had. Apart from fuel pump failures, I've had no stumbling problems, but I do get very bad detonation (pinging) when gassing it up on dirt roads after riding slowly under light load for a day (often happens). I think the engine cokes up a bit, and a good squirt clears the problem. It seems much better since I blocked off the airbox flapper. In fact, the bike is (by the seat of the pants) marginally stronger everywhere since doing that mod, which is backed up by dyno figures by one owner. It's not much, only 1hp or so, but I'll take it! I have no real reason to alter the fuelling on my bike. Stock everything except the flapper and AIS, and it runs fine when all is well.