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Do most 4 stroke dirtbikes not feel smooth?

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My 2009 kx250f and my buddys 2012 yz250f both seem to run "rough" when giving it gas barely off idle. Is this just a 4 stroke thing?

 

Rob, all engines should in theory, run smooth. Unless you have a high lift cam profile, even those race bikes should purring. My guess is it could be bad fuel, with that ethanol crap in your tanks, mabe fuel filter clogging, or something more serious like your valves not being adjusted.

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That is the hardest area in the throttle range to get perfect fueling at.

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The fuel injection on my KTM is awesome. Perfect everywhere. I'm assuming it's similar on all the newer bikes. I really wish they'd fuel inject the two strokes. I know they are looking at direct injection because it offers a lot more benefits in a 2 stroke but even standard port injection would be a huge improvement.

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it might be that the leak jet needs a change. this is where the notorious 4 stroke bog comes from

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Ok well Im blaming the cold on it. Yesterday is when It was doing it. And it was really cold like 10F today it is alot warmer didnt look at the temp when I rode but I can tell that it was alot warmer. And it doesnt have the notorious 4 stroke bog. Im talking about when you barely turn the throttle and keep it there it is not "smooth". Its hard to describe lol

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Edit: I'm wrong.

OP, my 450 is awesome off-idle. Lugs around like crazy down low and I have never had an issue with bogging.

Maybe it's just how 4t 250s run or maybe both bikes have the idle set too low.

Edited by CincoBoy

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Both of those bikes are fuel injected. Should be no jets anywhere.

OP, my 450 is awesome off-idle. Lugs around like crazy down low and I have never had an issue with bogging.

Maybe it's just how 4t 250s run or maybe both bikes have the idle set too low.

 

Neither of those bikes are fuel injected 😉

Edited by BoxcarWilly
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Neither of those bikes are fuel injected 😉

Maybe it's because I don't care about 4t 250s, but I'm a little surprised since the 450 bikes of the same years are fuel injected.

When did 250s become fuel injected? Why'd it take so long?

Now I feel like an idiot.

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Maybe it's because I don't care about 4t 250s, but I'm a little surprised since the 450 bikes of the same years are fuel injected.

When did 250s become fuel injected? Why'd it take so long?

Now I feel like an idiot.

2010 for the KX and 2014 for the YZ.

The YZ was for people who preferred carbs.

Everyone makes mistakes 😉

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My CRF150R doesn't like when the throttle is held over idle even in neutral. Its either gotta be pinned or idling.

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My 2009 kx250f and my buddys 2012 yz250f both seem to run "rough" when giving it gas barely off idle. Is this just a 4 stroke thing?

 

It's a pump carb thing. Cracking the throttle shoots a stream of poorly metered & poorly atomized fuel into the intake. The roughness can range from noticeable to awful depending on how well the carb is jetted.

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My CRF150R doesn't like when the throttle is held over idle even in neutral. Its either gotta be pinned or idling.

adust the fuel screw

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It's a pump carb thing. Cracking the throttle shoots a stream of poorly metered & poorly atomized fuel into the intake. The roughness can range from noticeable to awful depending on how well the carb is jetted.

the op was asking about steady throttle. No pump shot then.

My 250 and 450f were smooth but I always tweaked the fuel screw for the weather.

Some bike's are smoother. My yamahas(400 and 450) were like Electric motors. Some bikes are more thumpy.

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My 13 kx250f is real twitchy as the throttle is barely opened.. like its hard to putt around at idle cuz it wants to be on or off. I'm thinking I may need to adjust throttle cable a little or something. My buddy's 13 rmz is much smoother as the throttle starts to open but the kawi is more like a light switch. Wants to be on or off... mostly ON!!! lol

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