New bike fouling plug

[DWC81]

Hello everyone,

I'm new to the forum and need some quick advise.

I bought my 13 year old son a CR85R yesterday. He road it yesterday according to normal break-in procedure. Today he was riding it (I wasn't around) and he said it got real sluggish and died. When I got home I mixed up some gas (Castrol 2-Stroke Oil) 32:1 and filled the tank. But before I put the gas in I did see a little bit of gas sloshing at the bottom of the tank. It started right away and let it warm up a couple of minutes. Started reving it up and it fouled the plug. Cleaned the plug and it started right away again but everytime I start reving it up it fouls. Mixed up some more gas at little leaner on the oil but still fouls. It will set and idle with no problems but everytime I start reving it, it fouls the plug. Will a new plug fix this or do you think something is wrong with the carb? The dealer is 70 miles away so I'd like to fix it myself if possible. It's been a while since I've had a 2-stroke and I know the carbs have changed a bit since I was racing but this problem has got me a little confused.

Any help would be great,

Thanks

 

[darringer]

The bike is probably jetted a bit rich from the factory. Some leaning out of the carb is in order. Also, Using less oil in the mix will make the carburetion problem worse, making it richer overall. Less oil = more fuel. A new plug will help for a very short time. It will foul again fairly quickly unless leaner jets are installed. try adjusting the air screw on the side of the carb. Turning it out to a maximum of about 3 turns will lean out the slow speed circuit and could keep it from fouling.

 

[Octane250F]

One other thing to note too is that if your son it putt-putting around you can expect it to foul out plugs often. Thats one of the downfalls of a 2-stroke.
If he winds the motor up every now and then it will help the sparkplug to last longer. You could mess around with leaner jets and hotter plugs all you want, but my suggestion would be to have your son wind the motor up at least every now and then to clean the plug.

 

[mx966]

I agree with Octane250f. a 80 only runs good when pinned.

 

[mideastrider]

If you think thats the problem that he's not running the rpms high enough. Get a 14tooth front sprocket and run it awhile til he gets a little more seat time. It will be easier to keep it in the upper rpm range.

 

[Octane250F]

At the same time though, make sure he knows not to scream it all the time. Thats not good either...

 

[darringer]

If the bike is jetted right, it won't foul plugs. Especially since he's not riding it "on the pipe" it needs to be leaner. I have had numerous 125s that I used to ride slow goat trails with and never fouled plugs. They would literally be idling or near idle for long stretches with zero problems. They all would idle well, too. Another option is to run a spark plug one step hotter to help it stay cleaner.

 

[DWC81]

OK, I went and got a new plug and it ran ok. Still smoking a little bit even after it's warmed up. I'll start doing some searches about jetting this specific bike. I had a talk with my son (again!) about not lugging it around and not turning high rpms unless it's still pulling through the gear. I'll try a hotter plug until I can get it jetted properly.

Thanks everyone for your responses!

David

 

[KDX CRAZY]

Agree with turning out the air screw maybe one turn .

Also try dropping the needle by lifting the clip one notch , It will lean the 1/8 to 3/4 throttle range , until you get all the jetting sorted ( may even solve your problem )

 

[crazshane]

I agree with all of them. I have a yz85 and in the beggining when I first started I had to rev it a bunch so that I didn't foul the plug. Now it's just not fast enough for me. I never fouled the plug, and the thing is awesome. Plus, if it is new, you gotta expect it to smoke. It'll be fine as long as he rides that thing and gets it up into the powerband. ;)

 

[snb73]

Most new bikes come jetted rich from the factory. Jet the bike to your sons riding style and it won't foul plugs. Leave the premix at the manufacturers suggested ratio. 32:1 is good for and 85. I've had the same plug in my bike all year with out fouling.

Good luck, Steve.

http://ericgorr.com/techarticles/carbtuning.html

http://justkdx.dirtrider.net/carbtuning.html

http://www.strappe.com/plugs.html

http://www.ngksparkplugs.com/techinfo/spark_plugs/techtips.asp?nav=31000&country=US

http://www.keihin-us.com/tune.htm

http://www.powroll.com/tech_specs_jetting101.htm