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Discussion Starter #1
Hey guys back again, I took my Kawasaki prairie 400 4x4 (1998) out for a ride yesterday and I noticed when I got back that there was a lot of oil in the air filter box, to the point that the lid of the air box had oil on it. Also my Atv doesn’t go past 20 something mph. What’s can this be?
 

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Oil in the airbox comes from the crankcase vent line. If there's oil coming up out of it, it means it's been upside down, doing wheelies, or had pressure in the case. You get pressure in the case from piston ring blow by, or from overfilling the oil.

Did it just start going slow, or did you mean that you never go fast with it?
 

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Discussion Starter #3
Since I bought it’s never passed 20 something mph, idk why and now this happen
 

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I'm not sure if the 400's have the same limp mode system as the 650 and 700, but that would limit it's speed if it does. Pray it's that and not a completely shot cylinder.
 

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Discussion Starter #8
I just searched up and the 400s don’t have limp mode. You think the cylinder has to do with the oil in the air box?
 

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Pull the spark plug and see what it looks like.
If it looks bad, run a compression test.

Pull the belt cover and see if the belt is loose.
 

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Discussion Starter #10
I checked the belt it’s does fine in neutral rev up perfectly but when in gear the front clutch only goes in a little bit not as much as in neutral
 

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I just searched up and the 400s don’t have limp mode. You think the cylinder has to do with the oil in the air box?
Like I said, if blow-by is getting past the rings, it will pressurize the case. This pushes oil into the airbox.
Blowby occurs because the rings are not sealing off against the cylinder wall.
 

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If that’s the case I need to replace the rings? Or other stuff as well
Pretty hard to get that kind of blow-by without it showing up on the spark plug. Run a compression test anyway.

The primary clutch isn't going in under throttle in gear?
 

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Discussion Starter #18
Pretty hard to get that kind of blow-by without it showing up on the spark plug. Run a compression test anyway.

The primary clutch isn't going in under throttle in gear?
75445


this is what the spark plug looks like when I took it out
 

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1998 Prairie 400 4x4, 2001 Prairie 400 4x4, 2008 Brute Force 650 4x4
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Here is what my Tech Spark service manual says compression should be: Cylinder compression (usable range) 57-97 psi @500 rpm with electric start. I have the same 4 wheeler you have. I have only had it a couple months and just got mine running a couple weeks ago. I had to put a set of rings in mine, it had low compression and would not run when I got it. It's doing fine now.
 
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