CR250 Fouling Plugs HELP!!!

rendlish · Jul 30, 2007

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.

hot125mod · Jul 30, 2007

get the kehin carb and jet it

oldguy · Jul 30, 2007

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

mkelly04 · Jul 30, 2007

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.

rendlish · Jul 30, 2007

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.

rendlish · Jul 30, 2007

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.

j.lawson · Jul 30, 2007

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.

griffbones · Jul 30, 2007

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 · Jul 30, 2007

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.

yankeefan4life72 · Jul 30, 2007

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

steve.emma · Jul 31, 2007

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:

magneto · Jul 31, 2007

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.

rendlish · Jul 31, 2007

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.

mox69 · Jul 31, 2007

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 :)

2strokerfun · Aug 1, 2007

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.

rendlish · Aug 1, 2007

2strokerfun said:
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.

I noticed a certain pattern when the bike starts fouling plugs. It usually runs strong for about the first hour of riding, then after an hour it starts to foul about every 20 min. I figured a jetting issue would be apparent earlier in the ride, when the engine wasnt warmed up yet. But maybe I'm wrong. It is very consistant when it starts fouling after the first hour. No matter if I am going balls out, every 20 min it will foul a plug.

griffbones · Aug 1, 2007

I am still betting on a stator assembly since I had a bike act the very same way. And it too was a Honda!

Have you pulled the plug to see what it looks like after only 20 or 30 minutes of riding time, before it starts fouling? If the plug looks good at this point it probably isn't the jetting, it is probably an electrical componenet breaking down once it gets hot, normaly causing an open winding in a stator or pulse coil.

rendlish · Aug 1, 2007

griffbones said:
I am still betting on a stator assembly since I had a bike act the very same way. And it too was a Honda!

Have you pulled the plug to see what it looks like after only 20 or 30 minutes of riding time, before it starts fouling? If the plug looks good at this point it probably isn't the jetting, it is probably an electrical componenet breaking down once it gets hot, normaly causing an open winding in a stator or pulse coil.

I havent pulled the plug before it fouls, but that is definitley a good idea in determining whether its the carb or not. I will try that for sure.

Does anyone know where I could purchase an after market stator? I 'm having trouble finding one online for a 2002 CR250.

steve.emma · Aug 2, 2007

just a thought here but... if you suspect its a faulty stator then it would have to be due to low voltage in the ignition system that is causing weak spark and therefore plug fouling right?
so one test you could do to check the stator is to remove the plastic cover on the end of the rc valve motor (1 screw holds it on) then after 1/2 hour of riding when you think its going to start fouling etc.. check if the rc valve moves the cables when you rev the bike while it on a stand. if there is not enough voltage from the stator to run the ignition then there will not be enough to move the rc valve motor.
if you wanted to get more in depth you could check the stators output voltage when cold and when bike has be ridden for 1/2 hour and see if the voltage drops off when its hot.
i have a wiring diagram here for the 02' cr250 if you need a copy, all you would need is a voltmeter and some basic skill.
good luck.

whenfoxforks-ruled · Aug 2, 2007

http://dirtrider.net/forums3/showthread.php?t=92818, http://dirtrider.net/forums3/showthread.php?t=48348&page=1&pp=20, http://dirtrider.net/forums3/showthread.php?t=5308, I wish all the plug pics worked! Before you continue assaulting your bike with tools,sit down and read,a couple of times! Your bike needs to be properly jetted! It sounds like you have done everything else,now its time to get to the basics!

mkelly04 · Aug 2, 2007

whenfoxforks-ruled said:
http://dirtrider.net/forums3/showthread.php?t=92818, http://dirtrider.net/forums3/showthread.php?t=48348&page=1&pp=20, http://dirtrider.net/forums3/showthread.php?t=5308, I wish all the plug pics worked! Before you continue assaulting your bike with tools,sit down and read,a couple of times! Your bike needs to be properly jetted! It sounds like you have done everything else,now its time to get to the basics!

No offense, but if the jetting was spot on before, and the jetting is spot on for the first 30 minutes of the ride, then I dont think this is a jetting problem. Changing the jetting before finding the real cause will only hose the bike up worse.

mtk · Aug 2, 2007

Assuming it isn't a jetting problem to start with, which I'm not convinced is correct.

He hasn't opened up the carb in years.

Float level can change over time, which will hose the jetting.

There is also no evidence that the jetting is "spot on" either. I've seen plenty of 250s that were jetted horribly, but still ran halfway decent. With the amount of power a 250 has, even a poorly running example will still feel pretty strong.

If the jetting is slightly off, it could take 30 minutes to foul a plug.

The smart money checks the obvious things first. With fouled plugs, that means jetting.

steve.emma · Aug 3, 2007

He hasn't opened up the carb in years.

actually he said that he had recently....

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).

...and it sounds like he did a pretty thorough job. however i do agree that jetting is worth trying as that model is jetted rather rich stock anyway (main380,pilot32.5,needle-74).

i would think though if he can still foul a plug after 20 min of hard riding something else is at fault here.

whenfoxforks-ruled · Aug 3, 2007

If you have a manual and a multi tester you can rule out electrical issues,99 percent of the time! That 1 percent can be a real bummer,make sure! Leak down and compression can rule out a couple things.Replace the float valve,its 6 years old! If you need to change the jets more than a couple of sizes then I would be suspicious of bizarre electric problems,bad crank seals or a coolant leak. Throwing electric parts at the bike on hunches can be expensive,jets are cheap.

mox69 · Aug 3, 2007

Well about 8 people have suggested jetting to him so far.

Like others have said just because the bike ran good before is not an indicator that the jetting is perfect.

Unless he is riding his bike in a temperature / humidity controlled biodome and distilling his own gas the jetting is a good place to start!

But hey, if he wants to buy stators off f33bay and swap them feel free. Maybe he'll get lucky :)

CR250 Fouling Plugs HELP!!!

rendlish

hot125mod

oldguy

Always Broken

mkelly04

rendlish

rendlish

j.lawson

griffbones

mtk

yankeefan4life72

steve.emma

magneto

rendlish

mox69

2strokerfun

rendlish

griffbones

rendlish

steve.emma

whenfoxforks-ruled

Old MX Racer

mkelly04

mtk

steve.emma

whenfoxforks-ruled

Old MX Racer

mox69

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