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Author Topic: CR250. Random bog issue?????  (Read 8281 times)

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Offline redrider611

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CR250. Random bog issue?????
« on: January 02, 2013, 08:20:24 AM »
Ok guys, here is the situation.
2004 CR250. Bike runs great (crisp and clean) for several laps (5-10) and then all of a sudden it has a random bog for a split second.
It will usually happen in the whoops or on landings.

Things that have been checked already:
PV is working fine (even eliminated it) and it still does the same random bog
Float level at different settings
reeds are new and sealing fine
no air leaks found
kill switch removed
CDI changed


the bike ran great before and all of a sudden it started this. I am lost.
I hope someone has the answer for it.

Thanks 
« Last Edit: December 31, 1969, 04:00:00 PM by ' »
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Offline arnego2

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CR250. Random bog issue?????
« Reply #1 on: January 02, 2013, 11:30:46 AM »
How about the coil that would be my candidate.
« Last Edit: December 31, 1969, 04:00:00 PM by ' »
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Offline eprovenzano

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CR250. Random bog issue?????
« Reply #2 on: January 02, 2013, 02:30:51 PM »
It seems to be electrical, so I'd try the coil, and also a new plug.
« Last Edit: December 31, 1969, 04:00:00 PM by ' »
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Offline SachsGS

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CR250. Random bog issue?????
« Reply #3 on: January 02, 2013, 04:15:01 PM »
It's been my experience that an electrical problem can fool you into thinking it's a carb. problem and vice versa. Check for play in your crank and carefully examine the magneto side crank seal.
« Last Edit: December 31, 1969, 04:00:00 PM by ' »
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Offline _X_

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CR250. Random bog issue?????
« Reply #4 on: January 02, 2013, 09:05:26 PM »
could be caused by fuel splashing around (fuel starvation) in the float bowl. i think that is a reason boyesen made the super bowl http://boyesen.com/super-bowl.html
« Last Edit: December 31, 1969, 04:00:00 PM by ' »
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Offline redrider611

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CR250. Random bog issue?????
« Reply #5 on: January 03, 2013, 02:45:19 AM »
I forgot to mention that I had already replaced the left crank seal and it still did it.
I have also ran 3 different carbs with no luck.
I have also changed the coil and again no luck.

It is an absolute random bog.

I am going to be spiting the cases tomorrow to check for cracks internally causing a random lean issue.

Starting to think it needs holy water in the rads....
« Last Edit: December 31, 1969, 04:00:00 PM by ' »
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Offline Stusmoke

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CR250. Random bog issue?????
« Reply #6 on: January 03, 2013, 05:19:12 AM »
Your airbox isnt sucking in dirt is i? Theres no signs of coolant burning in the cylinder?

Also check the fuel shut off valve filter thats on the tank. If thats filthy dirty there could be dirt getting into your fuel and therefore, into your jets. Hence the random bog. If its filthy dirty, clean it (duh) and leave your bike to idle for about 10 minutes then come back and pull it off. If its disgusting again, you sound experienced enough to know the rest.

The force you take on when you plow through whoops or take big landings could be enough to force some of the dirt that might be in that filter through it.

Good luck. Exhaust ALL of the simple options you or anyone can possibly conceive before you start splitting anything :P
« Last Edit: December 31, 1969, 04:00:00 PM by ' »
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Offline 2T Institute

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CR250. Random bog issue?????
« Reply #7 on: January 03, 2013, 11:13:31 AM »
Quote from: racer x on January 03, 2013, 05:05:26 AM
could be caused by fuel splashing around (fuel starvation) in the float bowl. i think that is a reason boyesen made the super bowl http://boyesen.com/super-bowl.html

My thoughts as well also set the float height to be just before fuel comes out the overflow. Save yourself the grief of splitting the cases.
« Last Edit: December 31, 1969, 04:00:00 PM by ' »
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Offline SachsGS

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CR250. Random bog issue?????
« Reply #8 on: January 03, 2013, 04:18:52 PM »
Is the vent on your gas cap plugged?
« Last Edit: December 31, 1969, 04:00:00 PM by ' »
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Offline redrider611

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CR250. Random bog issue?????
« Reply #9 on: January 04, 2013, 03:54:11 AM »
All things have been checked and rechecked.
I have used 3 different carbs with float levels set and it still does it.
All vent tubes breath fine, no holes in float, etc.
coolant is not getting into the combustion chamber either.

It is really strange. On average I build 1-2 motors a week and I have never seen anything like this before.
It bugs the crap out of me too.
« Last Edit: December 31, 1969, 04:00:00 PM by ' »
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Offline Stusmoke

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CR250. Random bog issue?????
« Reply #10 on: January 04, 2013, 04:39:35 AM »
You said you changed coils right? I'm guessing you changed sparkplugs too? Have you googled around for anyone of the same year model having a similar issue? How accurate is your jetting?
« Last Edit: December 31, 1969, 04:00:00 PM by ' »
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Offline 2T Institute

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CR250. Random bog issue?????
« Reply #11 on: January 04, 2013, 11:31:29 AM »
Quote from: redrider611 on January 04, 2013, 11:54:11 AM
All things have been checked and rechecked.
I have used 3 different carbs with float levels set and it still does it.
All vent tubes breath fine, no holes in float, etc.
coolant is not getting into the combustion chamber either.

It is really strange. On average I build 1-2 motors a week and I have never seen anything like this before.
It bugs the crap out of me too.

Is your pilot jet a bit rich or lean, as this seems to be a heat related issue. Could it be once heat soak occurs your jetting is to rich off the bottom?
« Last Edit: December 31, 1969, 04:00:00 PM by ' »
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Offline evo550

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CR250. Random bog issue?????
« Reply #12 on: January 04, 2013, 02:41:01 PM »
Have you checked your carb floats for cracks ?
My sons YZ 85 had a similar problem, turned out after much investigation that there was a small crack in the float that would slowly fill up with fuel causing the level to change, creating a bog you described.
« Last Edit: December 31, 1969, 04:00:00 PM by ' »
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Offline SachsGS

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CR250. Random bog issue?????
« Reply #13 on: January 04, 2013, 04:58:51 PM »
Will the CR run with the choke on when the motor is at operating temperature? If so leave the choke on and see if it still happens.

Recently I repaired a neighbour's YZ 125 that has, if I am not mistaken, a Mikuni TMX carb that is similar to what you have on your CR. The YZ had a similar "bog", but more pronounced, than your CR. The bog went away if I left the choke on but it was obviously too rich and couldn't be ridden that way.So fatten up the pilot and all will be fine? Nope. I didn't want to waste a lot of time jetting the bike (time I didn't have) but something was not right. A freind had a similar problem with his TMX equipped Husky WR250 and he ended up putting a Keihin on the bike after wasting a lot of money trying to jet the Mikuni to no avail.
« Last Edit: December 31, 1969, 04:00:00 PM by ' »
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Offline TMKIWI

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CR250. Random bog issue?????
« Reply #14 on: January 04, 2013, 11:06:17 PM »
Does it happen at only 1 track , or does it happen everywhere.?
Reason I ask is I have had problems with some outboards having a random missfire and after countless hours of wasted time went out with them and found it only happened at 1 spot on the water.
It turned out to be electrical interference from an under water cable.
Strange but it does happen. That is why you see all the different electrical standards on CDI's.

Radio and/or electrical interference is so rare these days it can take awhile to diagnose it.
But it does happen..

If it happens at any track , disregard the above. :)
« Last Edit: December 31, 1969, 04:00:00 PM by ' »
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