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Old 06-17-2007, 07:50 PM
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Default 98, Cr 250 idle, HELP!!!

I am sure this question has been asked a thousand times, so please direct me if needed. I bought a 98 CR 250 last week and I am a total rookie with respect to a 2 stroke bike. Today I rode with my son, he on his 50cc me on the 250. We had a blast ripping up Garandma and Grandpa's farm, all was great until we did some trail riding where I was destin to 1 and 2 gears. The idle on my 250 is up and down constantly (rev... rev... rev..) you get the idea. This of course makes trail riding very unpleseant, if not darn right worthless. If I crank the throttle she barks and stretches the arms (runs great), but once back to idle I get the rev... rev... rev... again. It doesn't seem to happen (as bad) when the engine is cold, but has become intolerable once the engine is warm. Is this normal for this engine? Is it a carb adjustment? Do I need a rebuild? HELP PLEASE!!!!
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Old 06-18-2007, 08:00 PM
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Default Re: 98, Cr 250 idle, HELP!!!

I checked the slow speed mixture, it was set at two turns out, the factory setting. I started the bike and got the same idle response once the engine was up to temp. I then turned the slow speed mixture in slowly about one full turn and got a nice smooth idle. I let the bike idle for at least 15 min and it continued to idle smooth. I could not take it for a ride because of where I live, but hope I have cured the problem. Now on to my next question. While the engine is sitting idling, I think is has alot of mechanical noise (rattle, piston slap, etc..) How much is normal??? I know this is a tough question to answer without knowing a bikes history or hearing it, but other two strokes I have don't make this much noise. Next question, I am running 40:1 Amsoil with 93 oct and have plenty of smoke out the pipe as well as black oil sputtering out the muffler and between the muffler and pipe joint. Is this normal? Please forgive my ignorance, my gut tells me this is not correct though.
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Old 06-18-2007, 08:19 PM
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Usflag Re: 98, Cr 250 idle, HELP!!!

The CR250R isn't known for its low end performance. Jetting is difficult at best. There are a few threads by "Faded" in the Knowledge Base forums related to setting the float level (important to all the rest of the jetting adjustments being successful) and to jetting a bike correctly.

Some success is had after getting these sorted with going a few teeth larger on the rear sprocket, a pipe like the FMF Gnarly, a spacer for the exhaust at the cylinder and a reed block spacer. I hope Faded sees this thread or you might P.M. him with some background and your question. He is a really great person and one of the most knowledgeable people I know of for mechanics.

Bill
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Old 06-18-2007, 09:07 PM
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Default Re: 98, Cr 250 idle, HELP!!!

Quote:
Originally Posted by 80stars View Post
I checked the slow speed mixture, it was set at two turns out, the factory setting. I started the bike and got the same idle response once the engine was up to temp. I then turned the slow speed mixture in slowly about one full turn and got a nice smooth idle. I let the bike idle for at least 15 min and it continued to idle smooth. I could not take it for a ride because of where I live, but hope I have cured the problem. Now on to my next question. While the engine is sitting idling, I think is has alot of mechanical noise (rattle, piston slap, etc..) How much is normal??? I know this is a tough question to answer without knowing a bikes history or hearing it, but other two strokes I have don't make this much noise. Next question, I am running 40:1 Amsoil with 93 oct and have plenty of smoke out the pipe as well as black oil sputtering out the muffler and between the muffler and pipe joint. Is this normal? Please forgive my ignorance, my gut tells me this is not correct though.
Curious, do you know what jet sizes you are running? It sounds like it's really rich.
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Old 06-18-2007, 09:14 PM
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Default Re: 98, Cr 250 idle, HELP!!!

In my limited experience, the slow / trail riding will load up the motor, if jetted right, and I just assume this is correct, a few blips of the throttle will clean it out for the most part. Keeping in mind these were built for racing, i.e. lots of throttlel, and not crawling around in 1st or 2nd gear at slower speeds. I do very limited trail riding, and found that I had to lean out the pilot circuit, and the needle, i.e. move the clip up, this applies to both my KX250, and my Son's 99 CR250..also the air screww needs to be adjusted accordinly.

Altitude, air temps, and humidity all play a part in te jetting process, so what may work for one ride, may not be the hot set up for another.

Oh, and I believe that you can mix Amsoil a bit leaner than 40:1 I run Golden Spectro synth at 50:1
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Old 06-19-2007, 10:12 AM
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Default Re: 98, Cr 250 idle, HELP!!!

Stars
You don't mention it, but the idle is set on your carburetor using the enrichening valve or choke. I have had problems with all the PJ keihins I have owned back to 88. As that little piston and the carburetor body wear, it is really hard to get a consistent idle without making a rich running condition somewhere in the 0 to 1/4 turn/throttle area.

It sounds like yours is running really rich. The only way I have been able to make the pj idle right and set the low speed is pretty time consuming and it doesnt last long as it changes literally with the weather. To do it, I warm them up, set it to idle with the cable adjuster as opposed to the enrichenor, and then set the low speed screw to where it idles it's fastest. To ease starting once I have it at that point, I turn it back in (towards richer) until the engine just barely changes speed. Just barely. I do all this with the enrichening screw turned all the way down. Now, if you want a little play in the throttle cable you will have to deal with setting the final idle with the enrichenor per the manual. I really don't like the PJ carburetor for that reason. Once those pistons wear, (the first couple of seasons always did it on mine) you have a problem with over fueling at low speeds or when you close the throttle on high speed shutdowns, then a burble etc as you come back on the throttle. They get to the point of fouling plugs a lot if they are set to idle (if 'B' reads this he will be screaming I told you SO!!) when they get that wornout. If yours gets to that stage you either change the carburetor out for something like a PWK, screw the enrichenor down tight, or live with it. In the case of screwing the enrichenor down all the way, you wont have an idle without setting it with the cable. Quite a few people dumped the Mikunis that came on the 2001 and newer bikes (I gave one away) for PWK's. For your use you may really like one, they can be had cheaply when found.

Set the float at 16mm while you are deciding what to do. Going to something in the 16.25 range of setting helps some of the over rich running at trail speeds, but leans your top out some too, so if you try that just keep an eye on your plugs for the signs of lean top end running. Remember though, to make any idle and low speed adjustments you need to ride it until you are up to operating temps. While you can get the water temp up to operating temp, you wont be getting the case up to temp on the stand. (I am guessing like me you dont have a dynomometer at home or something similar.)
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Old 06-19-2007, 10:21 AM
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Default Re: 98, Cr 250 idle, HELP!!!

Quote:
Originally Posted by ossagp1 View Post
Once those pistons wear, (the first couple of seasons always did it on mine) you have a problem with over fueling at low speeds or when you close the throttle on high speed shutdowns, then a burble etc as you come back on the throttle. They get to the point of fouling plugs a lot if they are set to idle (if 'B' reads this he will be screaming I told you SO!!) when they get that wornout.


I always hated those PJ's and part of my "no idle" tuning mentality may stem from those stupid carburetors. I always tuned them like Ossa says, I'd turn the idle/enrichener knob so the bike wouldn't idle at all, then I'd jet until the bike ran best, and if I was so inclined, I would adjust idle at the throttle housing.
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Old 06-19-2007, 10:34 AM
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Default Re: 98, Cr 250 idle, HELP!!!

NOW I get the connection!! That carburetor would make anyone hate a bike that idled! (If I hadn't used my leftover Jikov carburetors as halibut fishing weights I may have replaced a certain pj with one of them.)
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Old 06-20-2007, 04:03 AM
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Default Re: 98, Cr 250 idle, HELP!!!

Dang you two are masters at spitting out good information. Ahh I can hear the foul language right that was used to tune that carb
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Old 06-20-2007, 08:07 PM
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Default Re: 98, Cr 250 idle, HELP!!!

All GREAT tips. Thank you! I had a chance to get out on a track yesterday for about an hour. My idle setting seemed to hold decent through out the ride. The first thing I noticed was that the bike seemed rich to me when I would get hard on the throttle and make it through some gears though. I have no idea what jets are installed in the carb. Engine starts required a few more kicks than normal after the engine warmed up. I thought I might try and change the clip on the jet needle to lean it out one step and then reset my slow jet screw. Also am considering runing 50:1 Amsoil in the next tank to see what that will do. I should be able to put some trail miles on this weekend and will report back. If it becomes too much work, I will find a PWK.
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Old 06-24-2007, 09:35 PM
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Default Re: 98, Cr 250 idle, HELP!!!

Thanks again to all for the great advise, don't quit I need more. As I stated earlier, I got the idle under control by turning in the slow jet screw in to about 1/2 turn from stop. Then I adjusted the enrichener to set idle speed, by the way this is a PJ with the power valve. I am happy with a solid idle, but find the low end to be WAY too rich. I am spitting black oil crud out the muffler and pipe seals (guess this bike needs new muffler seals too) making a mess out of the case and rear end. So... what would you do? Make a paper weight out of the PJ and get a PWK (if so, give me a lead on a 38mm)? Clean the carb and rejet the slow leaner? Big trip comming up over the 4th and I'd like to solve this asap. Almost forgot, am I a dreamer to believe I can make a 250 crawl around trails in 1st and 2nd gear and still run correct.
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Old 06-24-2007, 10:39 PM
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Default Re: 98, Cr 250 idle, HELP!!!

Checked my jets tonight

Pilot 55 (factory)
Main 172 (factory 175)
Power Jet moves with 12v attached

Is in on the pilot screw really richer???
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Old 06-25-2007, 01:25 AM
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Default Re: 98, Cr 250 idle, HELP!!!

80 Stars-
You are not a dreamer to believe that your bike cannot run good on the trails in 1st and 2nd. I have a 98 Cr250 and I do just that with it. My jetting is all stock and I have an FMF fatty. I run pre mix at 32:1 and do not have troubles with the oily gunk build up.

My bike has suffered from this problem you mentioned, but I always described mine as a surge. The only time mine does it is when it is up to temps, and I pull the clutch in and let it go to an idle, or put it in Neutral. Eventually, it seems to level itself off. I believe I could benefit from a new carb as Ossagp1 told me to a long time ago. As of right now, my bike always starts on the first or second kick and I NEVER foul plugs. I have had this bike for years and used the same plug for over two years. The only reason I replaced it was because I like to do preventative maintenance.

Again, these bikes work great in the woods, just gotta have the stuff dialed in is all. And when you leave the woods to an open clearing, nothing like letting it rip.

hope I helped a bit,
Ryan
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Old 06-25-2007, 01:55 AM
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Default Re: 98, Cr 250 idle, HELP!!!

I still have yet to experience why every one hates the pj carbs so much, my bike runs AWSOME with the pj, and I always had one hell of a time trying to get my sleds pwk's dialed in So I guess for now, if it runs good dont mess with it!!
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Old 06-25-2007, 10:42 AM
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Default Re: 98, Cr 250 idle, HELP!!!

If you havent done it yet, I would definitely set the float. If the level is high it will run rich, pretty much no matter how much you change jets. Here is the surprise to me, and that is your low speed air screw is so far in towards rich to keep it idling right. Makes me think you have two things working here or trying to work against eachother. One is an air leak that your airscrew setting is making up for. It is more pronounced with the throttle closed and vacuum high). Usually that idicates a bad crank seal to me. You need a seal and a flywheel puller in that case.

That should get your air screw setting somewhere out at 1.5-2.0. If you set the float the rest of your jetting should clean up. The electrical controlled midrange jetting on that one goes lean when it quits working, so I never considered it a factor. If you get tired of it, disconnect and put a 1368 needle in.

There is a reason Honda was the only one using the PJ and a reason they finally quit. No one else would by them from their subsidiary company and they had lots of them on hand is my guess. If not for that set your idle with the choke feature it would have been one of my favorites. It was the biggest reason I found my KX 500's easier to use at altitude than I did my cr500 (which I far prefer riding).
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