03 CR250 Jetting and Clanking

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#1
Greets,

I just purchased a brand new 2003 CR250 and went riding this weekend. First thing that struck me was the fact the every time I'd hit the powerband and chop the throttle, it made a metalic clunk noise. Kinda like piston slap or something similar. I started wondering if this was due to the RC Valve closing making this noise or should I look further into this problem?

Also, I live in FL and noticed spooge coming out the back. Obviously this is a jetting issue I should be taking care of but can't seem to find a good baseline to start with.

Can anyone help me out?
 
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#3
I'm having the same problem with an 03 CR250. Sounded like detonation, so I tried jetting richer with both needle (clip) and main (several combinations.) I also tried a colder plug. None of the changes made the clanging go away. Bike runs great, but sounds like it's getting ready to come apart when I back off at the end of a long straight. Any help would be greatly appreciated here also.
 
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#4
Yeah! That's what mine does too! I wonder if this is normal for a CR250 of if it is a major problem about to crop up. It almost sounds like piston slap or detonation as mentioned.

And I haven't even changed the jetting yet. Bike is completely stock!
 

marcusgunby

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#5
The 125s come with a stupid loose piston-maybe the 250s do-look at the clearances for a good piston in the honda manual and compare to a yz/kx/rm etc.Bet you find honda say a good piston for the cr would be totally worn out compared to a yz etc.
 

fonz

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#7
Thats Honda for you. we had an 03 125 that could not stay together when in stock form we had to make some changes to it to run reliably. Honda did not want to know of the problem with their 125s.
 
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#8
Are you running pump gas ? Any bike can detonate if you run that poor quality, low octane, pump gas.
Get some C 12 and and lean it out a little and your bike will run like it's made to.

I highly doubt it's a "loose piston"...Just plain old detonation.

The Honda cr125 is one of the most reliable 125's around....Yamaha's are notoriously known for their amazingly SHORT top end life...

Raced two cr 125's for a full season(practiced 3 to 4 times per week and raced 3 different classes every weekend for a full year), top ends were changed at a bit longer intervals than the manual suggests and NEVER had an engine failure.
 

marcusgunby

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#9
whitesands you must be talking pre 01 cr125s-all the modern ones detonate on pump fuel.
 
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#10
So I'm hearing that CRs NEED race fuel? Regular 93 from the gas station won't do? Talk about a picky bike! my 99 RM125 runs fine on 87 even.

I guess I need to find a place that sells this C 12 now. I hope it's not too expensive.

I did notice that the noise was not there the first few laps but as soon as it warmed up, it started doing it again. That would definitely signal detonation/pre-ignition.

I'll try that and keep all posted.

Thanks
 

john stu

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#11
my 02 cr made the piston slap noise on the first ride after three rides i put in a wiseco piston even though the was was just broken in and the noise was gone ever seince
 

Dragmeistr

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#12
My '03 CR detonated under a load and made the same sounds you are talking about, C-12 fixed it.
 

CR_Dave

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#13
C12 Fixed mine. PLus the race gas made jetting a bit more consistent. I pay about 32-35 for a 5 gallon pail.
 
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#14
I too have an 03 CR 250 an have tryed just about every jetting combo and the bike now runs great, But I get detonation noise and it is really bad in fast mid throttle sweepers. Have tryed going richer in the mid throttle area but it just runs bad. Now I have broke the top of the piston on the exaust side from this and the bike does not seem to be lean anyware. I have never had a bike so hard to jet before. Any ideas?
 
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#15
I fixed mine by running the stock pilot and main with the 2002 needle in the middle clip with 1.5 on air screw, I found that the bike was sensitive to the air screw setting, but the needle was the cure, with that needle I was good from sea level to 3,000 feet 50 to 90 degrees, and only requiring air screw adjustments(and once a clip position change). All on pump gas.

By running the Keihin PWK carb, the bike had a bit "sharper power delivery" everywhere, I just found it became too responsive for woods racing, and the Mikuni was actually giving me a bit less abrupt power which I prefer for woods riding. Good luck!