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botched porting job

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I bought a 2002 CR250, I went for 1 ride and it had almost no bottem end and kept loading up. My Dad has the same exact bike and it runs great. His bike definatly had more power than mine. I pulled the cylinder to put in a new top end and I found a botched porting job done by someone who thought they knew what they were doing. Do you think I could have a shop fix the porting or is it a lost cause and I'll have to buy a new cylinder?

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Yikes !!!   it does look like a rookie decided to take a dremel tool to it & might have done more harm then good.    From my experience once a cyl. or head has been tampered with a reputable tuner won't work on it.  

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Edited by H4L
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I bought a 2002 CR250, I went for 1 ride and it had almost no bottem end and kept loading up. My Dad has the same exact bike and it runs great. His bike definatly had more power than mine. I pulled the cylinder to put in a new top end and I found a botched porting job done by someone who thought they knew what they were doing. Do you think I could have a shop fix the porting or is it a lost cause and I'll have to buy a new cylinder?

i would have taken a compression reading before taking it apart. Although the work doesn't look real pretty, it's possible that it was only "cleaned" up a little. You can cc the head to tell how much material is gone. As far as cyl, was the piston/ bore worn?

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Somebody has really gone overboard with the porting and removed too much material, but i dont think its the main cause of your lack of bottom end. The port heights dont look like theyve been touched at all. The base also looks stock, so i would get '030 thou machined from the base which is the best mod to gain bottom end.

Also have you checked into other possible problems like jetting, rc valve, exhaust?

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That's some goober work. Port volume is increased & that can cause some low rpm power drop. As mentioned, there could be some other issues too. Lean jetting low compression, powervalves out of spec or jammed.

I would buy a new jug. A stock jug is WAY better than a crapshoot port job.

Edited by KPRacing
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Porting is exactly like back surgery. Only a very small pct is successful. Very small. A yoyo with a fancy tool does not a porting expert make.

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Porting is exactly like back surgery. Only a very small pct is successful. Very small. A yoyo with a fancy tool does not a porting expert make.

I would have to agree with that statement 100%.  Many engine tuners claim they know how do port work & in my experience I've dealt with some thru the past 30 yrs. only to have a cyl. become a lg. paper weight... 

Edited by H4L

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what gearing do you have?  A 50 or 51 tooth rear can really help the feel of the bike if you are riding mostly tighter stuff.  You could send that cylinder to Eric Gorr, he would take measurements and give you options (or would be honest with you if it should be scrapped).

 

What exhaust do you have?  The stock exhaust is pretty good on these.

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trans side crankseal? most trans oil stinks real bad you'd would probably notice the smell.if was burning it. monitor trans oil volume. if you only have 200cc left in trans,odds are..

lay a base gasket on cylinder mating surface and compare..

excessive overlap will be an indicator of how much material was removed..

do the same with the cases to verify as well..(pray the guy didn't 'work' on the cases too!) 

i'd be curious if your suffering from the fuel pooling..

the port windows i can make out look untouched..

 

given the hogging/volume issues,could the transfer be roughed up ,or bead blasted ? or would the finish of those ports be a non-issue? they look nearly polished..

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the effect of the surface roughness or finish on a port does not have that dramatic of an effect compared to moving the port windows or removing material from the runners.  If you do end up getting a new cylinder, upgrade to a newer year...there was something about those 2002 cylinders that wasn't great but I can't remember the details.

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The top of the exhaust bridge can crack if the engine is run hot. Lean jetting or a problem with the cooling system (low coolant, mud fouled radiators, ect). This doesn't always happen but it can. As long as the engine is NOT over heated, there really isn't a problem.

The 05-07 cylinders are less prone to this.

Obviously, over heating an engine should always be avoided.

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