2004 Bayou 250 bog down

[gt2003]

Changed oil and filter today.  Took it for a ride and it seemed to bog down or hesitate when i gave it gas.  Fresh gas too.  Any ideas?  I’ve had this machine since it was new.  Had carb rebuilt last year.  It runs great besides this.  I’m leaning towards maybe an exhaust issue but honestly, i’m not an engine guy so I’m just guessing.  It’s nothing major, it would serve my needs the way it is but there is obviously something a bit off.  Where should i start?

[Mech]

Well.. You could tell us a bit of it's history.. Like when it was last used, whether this problem's just started since the oil change(we hope not), whether it's come on fast or been getting worse for a while.. When it last had a service/tune. Does it roll nicely(brakes dragging perhaps).

You could sit on the bike and take not of where half way is on the throttle before you go for a drive so you can describe the throttle opening. Then, how much throttle were you giving it when it started failing, did it make a difference if you opened the throttle slowly, how far up in the revs, whether it could be coaxed past the flat spot or just got worse the further you opened the throttle. There are different circuits that operate in the carb and they go, idle, then from idle to about 1/4 throttle, then from 1.4 to about 3/4 or a fraction more(7/8 throttle), then full throttle. And, was it misfiring or just dull but steady, was it backfiring out the exhaust or carb.

You could open the drain screw on the bottom of the carb and check fuel keeps flowing out of there when the taps on, you could check the ckoke's working and going right off, you could check the air-filter's not too dirty. You could go for a ride up a hill so the engines loaded up to the point of struggling and keep it there for a few seconds then flip the kill switch and stop and take the spark plug out and see if it's black or white.

Give us more information and we can perhaps figure out where to start looking.

[gt2003]

Maybe i mis-titled this.  It doesn’t really bog down, it just hesitates when accelerating.  It works it’s way through the hesitations but they can definitely be felt.  I’ll ride it again today and see where it is on the throttle.    I don’t believe i notice it in 1st gear but 2nd and 3rd I do.  
I had the carb rebuilt by a local dealer before hunting season last year and it ran pretty good but maybe a little hesitation, it’s just more noticeable this year.  After hunting season I put stabilizer in the tank then ran it out of gas before storing in my garage.  I went ahead and drained all the gas yesterday before starting it, replaced w fresh gas and it started right up and idles beautifully.  After i changed the oil i let it warm up for a few minutes and took it for a spin.  Thats when i noticed the hesitation being a tad bit more noticeable.  After reading around, i pulled the spark plug and it was pretty fouled up.  Looks like it’s got the wrong plug too.  It’s got an NGK D8EA and looks like it needs a NGK DR8ES.  I’ll be replacing that today.

As far as backfiring, it doesn’t make any super loud pops but when i let off the throttle i can hear what i think is a small backfire through the exhaust.   
 

it rolls freely and the brakes aren’t dragging.

 

I think i covered everything.  Let me know if there is something I missed.  Appreciate it!

 

[gt2003]

Changed out the soark plug, disn’t make much different.  
1st gear, no hesitation but it does sound like it backfires/pops prior to shifting to 2nd.  In 2nd, the 1st part of the acceleration is where it hesitates again, does the same in 3rd.  When i parked it I’m pretty sure i smelled a little gas.  Would the blackened spark plug and smell of gas indicate maybe it’s running too rich?

[Mech]

Well if it's been parked up I'd definitely give it an hour of running hoping it was going to come right. That might just settle the valves and rings in.

Then the standard process would be to give it a general tune before deciding anything was wrong, plug, air-filter, check for any blocked caby vent hoses, check the idle mixture, maybe adjust the valves, check the exhaust system for leaks or blockage(some quads have a bung to drain the exhaust). If it's sat for a year it might just need a bit of oil on the air-cleaner if it's an oiled sort.

If you still think it's a bit hesitant then, it's possible the slide needle might need an adjustment, or the idle mixture needs a bit of a tweak.

[Gwbarm]

Was the hesitation the reason you had the carb rebuilt, and still there after the rebuild, if so, could be clutch related.

[gt2003]

Quick update.  I had a few

minutes today so I started it up, let it run for a bit and adjusted the carb/fuel screw out 1/4 turn.  There is still a very, very mild hesitation in 1st but none in 2nd, 3rd and 4th.  Looks like maybe it was just running a little lean.   I’m going to fine tune it a little more tomorrow but i’m very happy right now.

[Gwbarm]

Lean would definately do it, i run into that a lot with aftermarket carbs, and cant adjust it out, glad you were able to.

[Mech]

#7..  It's strange to have a bit of hesitation in first but not the higher gears..  Check the wheels/tyres are round and running straight, not buckled. That can cause a symptom just like very slight uneven running at slow speeds. And it goes away at higher speeds.