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Help with cr 310 jetting

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Jun 14, 2007
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#1
I just bored out my 1991 cr250 into a cr310 monster. I started richening the slow jet and needle jet 4 sizes richer, and the needle clip is two up. It now has some low end balls, I mean like ripping up the grass and pulling wheelies all through third with a practically bald tire. But now the top end just keeps bogging. Does anyone have any pointers on what I should set my jetting to? Thanks - JAYCE
 
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Oct 19, 2006
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#2
Does it bog as soon as you open it full throttle or does it accelerate to a point and then start to bog?

The needle clip is up 2 from the bottom of the clip? That puts it one slot below the middle, right? It might be time for a larger main jet. If the midrange runs well as it is right now, raise the clip on the needle some to bring that back to where its happy after enlarging the main jet.
 
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#3
It speeds up until it hits the top end, then it just kinda bogs. I believe the needle clip is on the second notch from the top. So if you're looking from the non tapered side its the second one from the taper. If you still think its the main jet, which I have reason to believe it is too, then how much larger should I start with?
 
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#4
From what I read, I don't think it's a jetting problem. Make sure the power valve is opening. A 91 CR is an HPP bike, those power valves are very prone to carbon seizing and somewhat difficult to set up properly. You can pull the cover on the left side and give the engine a rev. You should see the power valve snap open as the bike gets into the top end.
 
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#6
I'll have to check the HPP. Thanks for the info. It's not the plug, that's brand new. I'm sure its a air/gas mixture problem, I guess we'll see soon. Thanks guys
 
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#9
XR250rdr said:
Usually a bigger bore will want leaner jetting.

ditto that, larger pilot, leaner main.... and leave the needle where it was. when it goes flat on top that means to rich on main.