CR 250 1998 lack of power on hills

Hi I am having a strange problem with my bike and I hope someone can help, basically I rebuilt the bike and it ran great around the fields (on the flat) when I took it to the track a few weeks ago and found that it wouldn't even look at the hills, I had to drop down to first and eventually it stalled, I've stripped the carb and re-jetted it I've also checked the fuel flow to the carb which is fine, last night I even checked the compression which is just below the 160psi mark which I believe is fine. I'm hoping one of you guys have had a similar issue as I just don't have the funds to keep throwing at it just now, could it be the reeds??? Or maybe something else with the carb???

Check to see if the power valve is working properly, also check the reeds. The power valve might be stuck open causing severe loss of bottom end. You wouldn't notice it as much on flat as its not as hard to get the bike going. On a hill it would be more apparent

160 sounds a bit low, should be above 180

160 sounds a bit low, should be above 180

Really I did a bit of searching on this and was lead to believe anything over 150 was acceptable? I'm away the check the power valve will let you guys know in half an hour

Ok i think its the power valve, i removed the inspection cover and the groove is inline with (H) and according to the manual the grove should be vertical and inline with (L) Can the valve be de-carbonized with out having to remove the barrel? 

Edited by thorny78

Ok i think its the power valve, i removed the inspection cover and the groove is inline with (H) and according to the manual the grove should be vertical and inline with (L) Can the valve be de-carbonized with out having to remove the barrel? 

Yep, your power valve is stuck open

160 psi for a 250 is too low, and a stuck open pv wouldn't have any adverse effects up in the high rpm range, as that is the position it should be in. It would only affect the low rpm range. You should take the pipe off and check what the piston looks like. It does need a rebuild with that low compression...

160 psi for a 250 is too low, and a stuck open pv wouldn't have any adverse effects up in the high rpm range, as that is the position it should be in. It would only affect the low rpm range. You should take the pipe off and check what the piston looks like. It does need a rebuild with that low compression...

Ok thanks for the info although I never had a problem at high Rpm only the bottom end, the power valve is defo stuck open so going to pull the cylinder and might as well change the piston at the same time. Is there anything else you guys recommend I should do whilst I've got the cylinder off? Edited by thorny78

Just for another reference my 01 250 kicks over 200psi with a fresh top end.

Edited by izcain

You should be 180+ compression on your bike.  It will run clear down to 130 or so, but you are describing a lack of power and being down in the 150# of compression will definitely contribute to a loss of power.  You will also run warmer and eat more fuel.  That power valve is probably adding to your problems, but if it is stuck open it is just affecting low end power, not top end power.  When you did your compression test, how many kicks did you give it and were you holding it wfo?

You should be 180+ compression on your bike. It will run clear down to 130 or so, but you are describing a lack of power and being down in the 150# of compression will definitely contribute to a loss of power. You will also run warmer and eat more fuel. That power valve is probably adding to your problems, but if it is stuck open it is just affecting low end power, not top end power. When you did your compression test, how many kicks did you give it and were you holding it wfo?

Hi yeah I had the throttle wide open and gave it 10 - 12 kicks I'm going to pull the barrel and do a top end fresh up any how

Did you measure the the cylinder before? Did you bore and hone it? Did you match the piston to the cylinder. Also make sure your reeds are facing up.m and make sure they're not cracked.

Spray it down with some soapy water and see if you got a leak on a gasket

160 seems a bit low on a fresh top end.

150 is a "pass" but still rather low.

My 02 has 235 PSI when the top end is done. change rings when i drop 15% in compression.

160 seems a bit low on a fresh top end.

150 is a "pass" but still rather low.

My 02 has 235 PSI when the top end is done. change rings when i drop 15% in compression.

235psi... Not doubting that but the few top ends I have done have only been 195 tops 190-195. Just wondering year of bike and what your doing? Two top ends were on freshly repaired cylinders the last one on a cylinder that had been repaired previously. And I always check ring gap and usually have to file the rings down to get within spec using wiseco top ends.

Did you measure the the cylinder before? Did you bore and hone it? Did you match the piston to the cylinder. Also make sure your reeds are facing up.m and make sure they're not cracked.

The engine was rebuilt 2 months previous to me buying it to fit in my bike (receipts supplied with sale) I will be pulling the barrel within the next few days and will be measuring everything, bore, piston etc I will keep you guys informed of my findings

235psi... Not doubting that but the few top ends I have done have only been 195 tops 190-195. Just wondering year of bike and what your doing? Two top ends were on freshly repaired cylinders the last one on a cylinder that had been repaired previously. And I always check ring gap and usually have to file the rings down to get within spec using wiseco top ends.

Pro-x piston, ring gap set,AAANNNNDDD, seeing as Pro-x has 5 piston sizes to choose from i set my piston-cylinder gap perfect or a bit tighter then recomended.

I've learned the hard way from Craigslist.... Even if they have receipts it doesn't mean a reputable shop did the wrenching. Get a manual and a gasket kit an start tearing shit apart

I've learned the hard way from Craigslist.... Even if they have receipts it doesn't mean a reputable shop did the wrenching. Get a manual and a gasket kit an start tearing shit apart

Buddy that's exactly what I plan in doing Edited by thorny78

using wiseco top ends.

there lies your problem...the fact pro x has 5 different sizes makes it a better option if you have the tools to properly measure your bore and pistion. I know I'll get some crap but I'll personally never use another wiseco piston or clutch basket or  crank.  

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