2006 cr250 top end question

waitedawkins
Edited Date/Time 4/3/2022 8:00am
Hey guys im looking to get some advice on my 2006 cr250. I picked this bike up less than a year ago and finally got around to rebuilding it during December. I had shipped my cylinder head off to power seal to get re plated and they did a awesome job, i also bought a piston from them. Anyways i go the motor put back together, new top end and bottom end with a wiesco piston. I was able to get the bike running but i didn't want to have to deal with jetting so i bought a lectron carb. I have put about 2.5 hours on the entire motor when it failed on me. I was riding on a road coming back from where i was riding and i was in fifth gear and i wanted to give her the beans, which i did and i felt the power drop off and the bike sort of bogged but it kept running. You could say i was fifth gear pinned. I was able to get it back to where i needed to go and the bike died on me. I tried starting it again but it sounded like it had no spark so i pulled the plug and noticed the tip of it was missing (look at photos). I am running 91 octane pump gas with a 32:1 mixture of maxima castrol 927 oil with a lectron carb. I have inserted photos of the head, piston and spark plug. The plug is a ngk br8es. This is my first two stroke and first motor i have rebuilt so any advice on what went wrong and what i should do is greatly appreciated. By the looks of the plug looks like it was running rich but i feel like it was running to lean cause of the detonation again first two stroke for me. Thank you for reading.






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Paul_Pitzonka
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Paul_Pitzonka 4/1/2022 8:29pm
4/1/2022 8:29pm Edited Date/Time 4/1/2022 8:34pm
Definitely a lean problem... the center of the piston is beginning to melt... the BR8ES is a hotter burning plug than stock; combine this with the probable fact of a lean fuel mixture and I believe you have a descent starting point as to what caused it ... did you adjust the carb at all out of the box or did you just bolt it on and go?
JMCR250
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JMCR250 4/2/2022 7:05am
4/2/2022 7:05am
You were using the wrong plug. The 05-07 CR250s used a special NGK plug -- br9eg-n8. The "N8" part is important -- it's a different reach than the standard BR9 (or the BR8 you were using).

You may also have jetting issues, but the broken plug tip caused a lot of your damage.
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Paul_Pitzonka
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Paul_Pitzonka 4/2/2022 7:32am
4/2/2022 7:32am
JMCR250 wrote:
You were using the wrong plug. The 05-07 CR250s used a special NGK plug -- br9eg-n8. The "N8" part is important -- it's a different reach...
You were using the wrong plug. The 05-07 CR250s used a special NGK plug -- br9eg-n8. The "N8" part is important -- it's a different reach than the standard BR9 (or the BR8 you were using).

You may also have jetting issues, but the broken plug tip caused a lot of your damage.
I didn’t pay attention to the year... The br9eg-n-8 I believe has a thicker ground strap to prevent this exact problem; similar to the the late 90s rm 125 plugs
R66
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R66 4/2/2022 7:36am
4/2/2022 7:36am
Way too lean.
Didn’t you hear it pinging?

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Skerby
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Skerby 4/2/2022 9:02am
4/2/2022 9:02am
Had this same thing happen to a RM125 when I was a kid. You really need the right plug for some 2 strokes.
digger
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digger 4/2/2022 6:25pm
4/2/2022 6:25pm
I have owned a bunch of CR250's over the years, and current race 2 of them, an 06' and an 07'. What you are looking at there is a classic case of detonation. These engines are right on the edge of detonation stock, throw in some bad gas and a high load and lean main circuit and you have exactly what you are looking at. You have 2 options, use a mixture of some race fuel, say 2 gallons of 110 along with 3 gallons 91or 93, or take a squish measurement and send the head out to have the squish/ bowl reset for pump fuel only.
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MOTO557556
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MOTO557556 4/3/2022 6:07am
4/3/2022 6:07am
Also check the heat range on the plug, should be nine not eight.

(BR9EG-N-8) (NGK).
MXJIM10
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MXJIM10 4/3/2022 8:00am
4/3/2022 8:00am
Put stock carb back on. Stock jetting go from there. 250 usually run 8 plugs 125 are 9.
FGR01
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FGR01 4/3/2022 9:31am
4/3/2022 9:31am
As Digger and others have said, lean carb is main culprit. In my experience, Lectrons come tuned pretty close, usually within a few clicks, but generally on the lean side. I've installed a few where they were so lean the bike refused to start when it was cold out. So, I usually end up richening the metering rod a few clicks to get the low to mid correct and then tuning the power jet circuit to get the top end right. The problem is there is a very small sweet spot on both metering rod and the power jet. So if one or both is even a little bit off, it can cause a pretty bad leanness.

Even when tuned correctly, Lectron is generally a very lean carb, hence the excellent trail manners and high mpg's. But this means they are not a good idea for extended high speed, high-rpm runs like you describe.
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MOTO557556
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MOTO557556 4/3/2022 10:06am
4/3/2022 10:06am

MOTO557556
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MOTO557556 4/3/2022 10:21am
4/3/2022 10:21am Edited Date/Time 4/3/2022 1:35pm
Like the age old discussion about oil, ratio, and brand there are a lot of opinions. The screenshot above shows the proper plug for a 2006 Honda CR250R.

If you are running what could be suspect fuel, a lean Lectron setting at wide open throttle, and a hotter heat range plug/plug design than what the engine was designed for you have the equation for trouble.

Top of the piston, center of the piston, and lack of spark plug ground electrode all tell a bad story.



MXJIM10
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MXJIM10 4/3/2022 11:24am
4/3/2022 11:24am
Most 250s run 8 plugs. Honda being the exception. Looks like the carb is the main culprit here.
MP261
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MP261 4/6/2022 1:39pm
4/6/2022 1:39pm
I had the same problem running a lectron, was pinging and detonating on the top end. Adjusting the Powerjet didn't help that, so I richened the metering rod as per their recommendation and began fouling plugs. I ended up going back to the Mikuni after melting the Piston. All in all with trying to dial it in I put less than 10 hours on it and ended up requiring a full rebuild. That was with running an 8 plug. Buddy of mine has one on his RM and no issues at all.

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