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Kx85 bogging

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So today I had a race and practice and heat 1 went very well. After about my 2nd lap of heat 2 my started to bog down. I would try to give it full throttle it would bog down so I would kind of be choppy and then once on the power band it wasn't as boggy

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Warm weather?
Clogged air filter?
Guncked up power valve?

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On 6/19/2017 at 7:24 AM, numroe said:

Warm weather?
Clogged air filter?
Guncked up power valve?

I am thinking it might be the air filter because it never used to do this

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On 6/18/2017 at 7:13 PM, Bidulez said:

Did you try a new plug ?

 

 

On 6/19/2017 at 7:24 AM, numroe said:

Warm weather?
Clogged air filter?
Guncked up power valve?

Do you think it could be because I had it idling at the starting gate instead of revving it?

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1 hour ago, Damien_Kawasaki said:
Do you think it could be because I had it idling at the starting gate instead of revving it?

No. A mechanically healthy kx85 which is tuned correctly will cope with idling or low RPM use for as long as you wish.

Revving at the start is to clear out the case and get the cylinder and coolant temp up. For max power when you go.

Try a new plug and freshly oiled clean air filter. If the motor still runs a bit rough and you're confident your piston+rings are not worn out, and your muffler is clean inside, then you should try leaner jetting in your carb.

Which adjustments to do in the carb depends on at which throttle position you think the motor feels the most rich.

Below 1/4 throttle = pilot jet (go one size smaller)
Around 1/2 throttle = needle clip (lower the needle = clip higher)
Wide open = main jet (go one size smaller)

Maybe you choose to do a couple of adjustments at the same time. Your choice.

Ignore RPMs. Focus on feeling the motor at constant throttle. Pick a suitable fixed gear. Find a long uphill straight if you can, and hold constant throttle (1/4, then 1/2, then wide open for each run), then feel the motor's power as it pulls through a wide RPM range.

Rich or lean can cause a motor "bog".  Rich and lean cause different problems..

Rich does this:  Rough running, misfiring, blubbery, weak power, smokey, wont rev out.

Edited by numroe

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I have a kx85 2 stroke and it keeps bogging over half throttle that I give. I have cleaned the air filter and changed the spark plug again. The last time when I mixed my fuel it run fine but I don’t know if   my fuel mix is fowling my spark plug. What do you think it could be?

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On 6/8/2020 at 12:47 AM, Brady Rogers said:

I have a kx85 2 stroke and it keeps bogging over half throttle that I give. I have cleaned the air filter and changed the spark plug again. The last time when I mixed my fuel it run fine but I don’t know if   my fuel mix is fowling my spark plug. What do you think it could be?

If it previously ran fine, then you always have to ask the question "what's changed?".  A new spark plug and clean air filter were good starting points.

If it was stored for a while with fuel in the carb then maybe the main jet is a bit clogged with premix gum after the fuel evaporated.  Try a new one, in the same size, with 100% fresh fuel + premix oil.

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