CR250 Fouling Plugs HELP!!!

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#1
I have a 2002 CR 250 that I had bought brand new back in 02’. I have always run Honda HP2 synthetic racing oil with 93 octane mixed 32:1. The bike is all stock aside from my silencer. I have ridden this bike for years and NEVER had a problem until recently. The bike runs strong, but has been consistently fouling plugs, even under heavy riding. I am fouling on average about 4 plugs in a 3.5 hour ride. The plugs are wet with a film of gas and oil on them. I have never touched the carb, because I have never had a reason too. When it first started fouling plugs, I replaced the top-end, with a standard size piston and rings and I also replaced the reeds. It ran great but was still fouling plugs just as much. So then I decided to replace the clutch side crank seal. I know that it is possible if the clutch side seal is leaking, that it will draw tranny fluid into the cylinder, thus flooding out the plug. Well, this didn’t fix the issue either. So I then decided to tear apart the carb. There was absolutely nothing visibly wrong with the carburetor. It looked better than new inside, but I still removed all the jets and the choke, making sure everything was clean. I also checked the floats, which were not sticking. I put the carb back together and adjusted the air screw to 1 ½ turns out. (This is the stock setting that I have always used on the bike). I cleaned the airfilter and put a new BR8EG plug in it. Yet it is still fouling 3 or 4 plugs every ride. At this point, I am not sure where to start trouble shooting and my patience is running thin, along with my bank account from buying 4 plugs each ride. I also pulled the stator cover off thinking that maybe the flywheel cover was leaking water into the generator and causing a weak spark, which was causing the plug not to burn hot enough. The stator looks clean and free of corrosion. I haven’t actually taken it apart yet, but I was thinking of cleaning the brushes in hopes to strengthen the spark. Is there any easy way, or any way, to test the stator for malfunction? Also, my exhaust valve (RC Valve) has never been cleaned and could quite possibly be clogged up, but I didn’t think that would cause a rich condition. Any input on this issue would be greatly appreciated.

Thanks.

–Ryan.
 

oldguy

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#3
hot125mod said:
get the kehin carb and jet it
Why???
He has a perfectly good bike now just needs some TLC
When you had the carb apart I assume you used air to blow all the vents clean. Have you repacked the silencer? Doubt that would be the cause but it could back up the system if clogged.
At this point I'll step aside and let someone more familiar with 2 strokes take over
 
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#4
hot125mod said:
get the kehin carb and jet it
The bike just started doing it, that means there is something wrong besides the jeting.


You've probably already checked, but what is the condition of the spark plug boot? I've seen carbon build up cause the plug to make poor contact and foul out.

If thats not it, then I would try the rc valve, If its not working then the engine would not move as much air at high rpms so the bike would be jetted rich...... Since your rc valve is electronic I bet you can get it to open/close on the bench to test it.

Good Luck.
 
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#5
I havent repacked the silencer yet, I will give that a shot and see what happens. And yes I used compressed air to blow out the carb.
Thanks.
 
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#6
mkelly04 said:
The bike just started doing it, that means there is something wrong besides the jeting.


You've probably already checked, but what is the condition of the spark plug boot? I've seen carbon build up cause the plug to make poor contact and foul out.

If thats not it, then I would try the rc valve, If its not working then the engine would not move as much air at high rpms so the bike would be jetted rich...... Since your rc valve is electronic I bet you can get it to open/close on the bench to test it.

Good Luck.

The plug boot seems fine. I think the RC valve should definitley be cleaned. I am going to give that a shot and see if it helps. Thanks.
 
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#7
sounds like you'v really went through this thing. :bang:

since the plug seems so wet it sounds rich, but you said you.v kept it stock and checked that so.. I would check my spark plug wire and boot? ummm...maybe the kill switch, the wires going into and also the ignition set up, coil, stator, stuff you probly already know to check... float could be set wrong, to high?......try a hotter plug?

And I would definantly remove and clean your power valves.
 
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#8
I had a bike that just started fouling plugs really bad, and I had never fouled plugs in the bike before. Then one day it died to never start again, that is until I found the bad pulse coil and replaced the stator assembly. Just a thought.
 

mtk

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#9
Check the float bowl level.

It can change over time, which will royally screw up your jetting.

Beyond that, get over the idea that a carburetor is a "set it and forget it" apparatus, because it isn't.
 
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#10
I too have an '02 cr250 and have been fouling plugs.The stock jetting is rich.I recently switched to a kehin airstriker and could not beleive the differnce.MUCH more crisp throttle response. Even gave it more bottom end.Make the switch you wont be dissapointed!!I run 50/50 race pump gas with castor oil @ 40:1
 
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#11
it sounds like you have covered the basics pretty well. the keihin might run 'better' but like its allready been pointed out the bike used to run fine so changing carbs is not the issue.
remove and clean the powervalve but i doubt thats your problem, if it was seized or not working then there would be major running issues that you would notice like lack of top end or bottom end power etc..
this plug fouling could well be due to an electical issue i.e. poor spark. is the bike hard to start when cold? generator and pulse coils can be checked but its not easy to do and is best left to a dealer.a bad coil or cdi unit could also be the fault in either spark output or ignition timing, this is something that again is kinda hard to diagnose at home unless you have the correct tools and knowledge. if you had a friend with the same year cr you could try swap cdi units and see if that makes a difference.
lastly something you can do is check the coil to frame earth connections, then check the motor to frame earth connections etc.. as if these are bad this will effect spark.
good luck. :cool:
 
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#12
Other variables that may be causing your problem:

Gasoline consistency from refinery

Environmental (temperature and/or humidity)

Change your jetting until the bike runs correctly and don't worry so much about why it changed.
 
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#13
steve.emma said:
it sounds like you have covered the basics pretty well. the keihin might run 'better' but like its allready been pointed out the bike used to run fine so changing carbs is not the issue.
remove and clean the powervalve but i doubt thats your problem, if it was seized or not working then there would be major running issues that you would notice like lack of top end or bottom end power etc..
this plug fouling could well be due to an electical issue i.e. poor spark. is the bike hard to start when cold? generator and pulse coils can be checked but its not easy to do and is best left to a dealer.a bad coil or cdi unit could also be the fault in either spark output or ignition timing, this is something that again is kinda hard to diagnose at home unless you have the correct tools and knowledge. if you had a friend with the same year cr you could try swap cdi units and see if that makes a difference.
lastly something you can do is check the coil to frame earth connections, then check the motor to frame earth connections etc.. as if these are bad this will effect spark.
good luck. :cool:

I believe you are correct in thinking it is an electrical issue. I am going to tear it down this weekend when I get some time. My main focus at this point is the stator. I spoke with someone who was having the same problems I am having, and it turned out to be the stator. I'll let you know what I find out. Thanks for all the input.
 
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#14
From my experience most electrical issues are work / no work. That being said you still could very well have an electrical problem.


The only possible explaination I see from an electrical point of view is weak spark, or intermittent spark (ie misses every 5th revolution, or something really odd like that). I assume an experienced rider would notice a consistent miss like this, maybe not. I don't even exactly know how a miss like this would occur, but eh who knows. Check the electrical stuff out, but don't spend too much time or $$ here.


I think I tend to agree with the other poster said about gas chemistry changes + temperature changes + worn out silencer packing. Or some combination of those.

It's not unheard of to need to rejet when a new top end goes in. This is because you have gained some previously lost efficiency. Add the new top end to all of the other things and it is probable.



1. Check the electrical system. Measure the resistance of the spark plug wire. Do whatever the manual says to check the rest of the components.

2. Rejet the carb. You could spend tens of hours and hundreds of dollars to find the exact cause of this problem. If a rejet takes care of the fouling and has no other adverse effects, don't dwell on the cause :)
 
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#15
mox69 said:
From my experience most electrical issues are work / no work.
In my experience, this is true 99 percent of the time. I have had intermittent spark from bad ground and had a weak spark once because of spark plug cap. But other than those two occassions, it either worked or didn't work.

And I've had to rejet a bike that seemed to run perfectly well the week before.