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650R Weak Motor Blues

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I've been working on an XR650R for a buddy.  He picked it up used a couple years ago and it's always been plagued with motor issues.  I've been through the carb and it's jetted with all the recommended jets, and it has been "uncorked" by the previous owner.  Just recently, I went through the cooling system and found that the thermostat was bent, so it got replaced with a napa part with the recommended extra hole drilled in it.  The whole system was blown out and flushed with the evans prep and filled with Evans waterless.   What's my next step to figure out why it runs so weak?   What else should I be looking for?  It runs like a beast until it gets up to operating temp, then it bogs and the throttle response is crap.  Any suggestions?

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Carb has been all cleaned up, with nice new fuel.  Jetted for my altitude 68s pilot and 165 main and needle at position #3 from the top.  Thought maybe overheating was the issue, therefore the cooling system was overhauled and went with Evans which claims to be a better alternative than antifreeze.  It did have a bent thermostat, which would explain an overheat condition, but it didn't seem to fix the problem.   I haven't looked at valves yet, but it sounds like that would be my next step huh?

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The Evan's is actually a poorer coolant , it has less heat transfer. It won't boil over , even if your motor gets hot enough to fry  itself , but it won't boil over. You may actually be running hotter than before , which makes your jetting rich.

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Ok, compression is on the weak side.   Because I'm going to need to rebuild the top end,  would it be worth going with a big bore kit?   What else could I do while I'm in there to bring out the "animal" in this machine.   What are the Baja guys doing to those machines?   I see tons of parts online, but I want to hear from the guys that have tried them.

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You'll get more power from a compression bump than overbore. JE has an 11.0 piston for these and you should put a  stage 2 HotCam  in too. 

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If you are going high comp piston and stage2 cam....you better know how to use clay to check valve clearances at the piston..

 

just sayin.others in the past didn`t  :lol:

 

B

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Guess a valve adjustment is next. The problem still exists. Once it's nice and hot, it misses when you get on it. Any advice?

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On 5/11/2017 at 9:45 PM, Chadolson said:

What should my compression be? I'm showing 120 on the gauge.

I dont know but did you shoot oil in cylinder on a second try?  To see if there is a notable increase in compression which would tell you rings/bore is suspect.

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On 5/11/2017 at 1:39 PM, Chadolson said:

 It runs like a beast until it gets up to operating temp, then it bogs and the throttle response is crap.  Any suggestions?

My guess is ignition, check plug cap wire coil or any of the associated connections. Had a suzuki do it when the under tank coil got hot.  Check up in your plug cap for a removable resistor, remove with screwdriver. Those would drive you crazy too.

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Interesting. I'll take a look at compression and ignition components. Thanks for the suggestions!

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Ok, latest update.  Went through the carb again. All new everything in there.  Adjusted valves, the intake side, both were a bit tight, exhaust side is good.  Took a good look at the coil and visually it looks ok.  I'd like to find a donor to borrow just for comparison,  but isn't the coil one of those parts that are either good or bad?  Still need t look at the stator and CDI.  I've noticed there is a lot of threads about the XL stator having some soldering issues, but the XR looks like a different part.  I'ts not really exposed to high heat either, it's under the  seat...  Compression is not perfect, but should be acceptable to run relatively descent.  The manual isn't a lot of help with their troubleshooting guide.   Again, runs great until it's up to operating temp, then bogs when you get on it.  It's jetted for my altitude already.

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Does your left sidecover , over the air filter , have holes in it ? If not , try riding it with the cover off and see how it runs.

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Does your left sidecover , over the air filter , have holes in it ? If not , try riding it with the cover off and see how it runs.


Yea, it's been uncorked.

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