Question for the two stroke crowd!!!! :-D

Prokopchuk_9 · May 16, 2012

So I'm in cochrane Alberta, about 25 min NW of Calgary visiting my parents. I brought my cr250 2 smoker to do some mountain riding, it's now jetted for 900ft above sea level and it's about 4000-6000 where we will be riding. I'm new to the whole mountain riding scene. Now we went out today, the bike ran totally fine. No bog at all, completely bog free from top to bottom ran and started fine. BUT it will not idle!! Not at all. Now I understand jetting and know how I do it. I don't want to mess with the carb for just a couple rides just cus it won't idle. I know it might be running a little rich, less air so it's gettin more fuel. What's the worst that can happen?? Just a fouled plug right?? It's not smokin bad, I pulled the plug and it looked a little bit darker than usual but not too bad. Ground strap still had a touch of brown. Anyways just don't want anything bad to happen when we head way out in the mountains for a good ride this weekend. What's your guys thoughts? Should I just leave it? Maybe give the air screw a twist?

SouthCo · May 16, 2012

Other than a fouled plug shouldn't hurt anything. Like you said if anything will be a little rich. I'm not an expert but my son rides a 2 stroke KTM Pro Senior and it's turning me into a bike mechanic.

May just be able to adjust the idle screw if it has one. The KTM does.

Prokopchuk_9 · May 16, 2012

Nice thanks man! Ya I think I'm okay...I'm half decent. I can rebuild 2 stroke motors, intermediate mechanical skills i would say but no experience with high elevation jetting and or riding in the mountains LOL

oldschool327 · May 16, 2012

Just play with the mixture screw until you achieve the highest idle then back off a 1/² turn. Should be good

Squirrely · May 16, 2012

bring extra plugs just incase you foul one. I wouldn't rejet for a couple rides either.

When was the last time you put rings in that thing? If it is hard start or wont idle, it could be time.

Prokopchuk_9 · May 16, 2012

It's close to 40 hours on top end now, gobs of compression still. Starts first kick. Everytime. Hot or cold. 1000ft or 4000ft lol. Also stock jetting on this bike, won't idle.

NitroCherokee · May 16, 2012

Pack an extra plug or 2 and ride it

Squirrely · May 16, 2012

Tthe no idle is odd. My freind has a 89 that he's completely rebuilt. From the ground up, and it will not idle now... I have no idea why.

Every mx bike I've owned will load up in a few seconds and die. But they idle, sorta... for a 2 stroke.

Prokopchuk_9 · May 16, 2012

This bike can idle, it tries to. Once it's warm it will idle for a minute or two back home, eventually die out. This bike im on is completely built from the ground up as well, it's a nice bike. Just doesn't idle, I've read over on thumper talk that most 2 stroke mx bikes the correct jetting won't allow for a very strong idle...and it shows.

And now that I'm up 4000 feet, it doesn't idle at all. Not even a bit LOL...just stay on the PIPE so she don't foul out!! BRAAAAAP

dirtfan21 · May 16, 2012

Always better to be a bit rich than lean, I'd ruin a couple plugs before grenading a motor. I like what oldschool327 said, try that and see how it works out cause if she is not bogging out at WOT throttle or wanting to die on the low end grunts then no worries.

As others have said, don't waste your time trying to find the right jetting for that altitude if it will only be for a couple rides. My '03 KTM 250sx didn't want to idle until it was totally warmed at the jetting I felt most comfortable with.

Grab that throttle and crank! She will do just fine!

kdixer · May 16, 2012

A properly tuned bike should be able to idle. The main jet controls WOT. The slide needle controls mid throttle. The pilot jet and mixture screw controls idle to just off idle. If the bike runs strong everywhere but idle, you need to adjust the idle speed screw until it will at least try to idle and then adjust the mixture screw.

If a 2 stroke loads up and dies instead of idleing, then the carb is not adjusted right. Check out post #8 on the following link. That will walk you thru it.

http://www.allthingsmoto.com/forums/f-31/cr250-idle-screw-location-25328/

Doug_Scott · May 16, 2012

The way the idle is being described, I would make sure there are no vacuum leaks. An engine that is too lean will sometimes "hunt" when trying to idle.

2 strokes need to always have the correct fuel/oil mixture, too lean, and not having enough oil in the fuel, will not run long. Try to not run the bike too lean (both air and oil).

kdixer · May 16, 2012

It should also be noted that running too rich can be almost as bad as running too lean. Running too rich leads to excessive carbon buildup in the combustion chamber. Not only will that rob performance, but it often flakes off and causes scuffing on the cylinder walls. Carbon is abrassive when it is trapped in the moving parts of the engine. Runnig too rich will also cause fouling of the exhaust system and powervalve as well if your bike is equipped with one.

Prokopchuk_9 · May 17, 2012

Aahh few rides ain't gonna cause to much carbon build up!! That's over along period of time! I think I'll be okay for a few rides! Thanks for the knowledgable opinions though!

kdixer · May 17, 2012

Aahh few rides ain't gonna cause to much carbon build up!! That's over along period of time! I think I'll be okay for a few rides! Thanks for the knowledgable opinions though!

Yeah, I was not referring to your situation. I was mainly aiming that at the people that jet too rich on purpose because they view it as an added safety factor. runnign lean can cause problems quick, runnign rich can cause problems down the road. It is not that hard to get a bike running right, it is just a little time consuming.