01' CR250 Problems after rebuild

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Aug 24, 2007
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#1
I bought a rolling chassie a few weeks ago, it needed a top end so I picked up a rebuilt cyclinder, head and new piston/rings. The piston was for a 2005 and had only one ring as opposed to the orginal factory 2 ring piston. They took my old power valve out, cleaned it and installed in the new cylinder. I boilted it down and torqued to factory specs. Put a new air filter in and insured it was oiled. I loaded the radiator with 50/50 antifreeze and water. I didn't do anythign to the carb so am unsure whats in it for jetting. I installed new carbin power reeds as well. I'm running 50:1 premix with 94 pump gas. After taking it for a short ride, took the plug out and it looks perfect, a nice medium brown color.

Couple things that is odd.. I blow a little oil out the crack case breather tube, not a lot but enough to put some oil spots on my garage floor. Not sure if I put too much oil in or not.. Could this come out if I had too much oil in?

Also, I get a little surging, just quick (split second) surges when I'm off the throttle or am lightly on it. WOT seem's to be fine. At first I thought it was a knock, sounded like one untill I paid a lot of attention to it and its surging the engine in small bursts.

Idling Problem: I turned the air screw out the recommended 1 3/4 turn but this thing won't idle at all when its warm! There is another small screw with a nut to lock it in place, not sure what that is (I'm just a backyard mechanic).

I probably should have taken the carb apart and cleaned it up prior to testing the bike. The guy who had it before raced it, it came with an OMS Suspension on it so he probably rejetted the carb.

Any advice would be greatly appreciated!

Dennis
 
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#2
Took the carb apart today and cleaned it. noticed it had a 400 main jet and a S-9. I could get the spring loose to see what position the clip was on. if i pulled any harder, it was going to strech the spring. Tried everythign to get it out with no luck.

Got it back together and it fired up first kick.. Still the split second surges though.. :( Going to try 32:1 fuel mix and see if that helps (running 50:1 now).

Dennis
 
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#3
Wavfact said:
I bought a rolling chassie a few weeks ago, it needed a top end so I picked up a rebuilt cyclinder, head and new piston/rings. The piston was for a 2005 and had only one ring as opposed to the orginal factory 2 ring piston.
That's an interesting combo. The '01 uses a flat-top piston while the '05 piston is domed... There may be other differences as well. Did you check the squish clearance?

Wavfact said:
They took my old power valve out, cleaned it and installed in the new cylinder.

...

Couple things that is odd.. I blow a little oil out the crack case breather tube, not a lot but enough to put some oil spots on my garage floor. Not sure if I put too much oil in or not.. Could this come out if I had too much oil in?
The Service Manual recommends packing grease and Moly 60 paste around the different powervalve drive shaft components (parts 11, 12 and 14 below) during assembly to seal the clutch area off from the exhaust port.



If this isn't done properly, exhaust pulses can pass through the PV drive assembly and into the clutch area and could cause some tranny oil to be blown out of the crankcase vent. Here's what mine look like before assembly.





Wavfact said:
There is another small screw with a nut to lock it in place, not sure what that is (I'm just a backyard mechanic).
On the Mikuni, the screw with the lock-nut is the idle adjust screw.
 
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#4
I called the place I got the cylinder, head and piston from (which is well known for being the best around here) and he said I shouldn't have any problems with the piston..

He thinks I have an air leak somewhere.. I put a video together if anyone care's to take a look, maybe you have heard this before. I tried to put a link up but it won't let me even using the insert link button..

I did not pack grease in there when I put the cyclinder down.. is this going to hurt anything by not doing it or should I pull it back off and grease it up?

Dennis