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1989 CR250 ------- Idle?

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A friend just got an 89 Cr250 and I told him I would perfect the jetting. It doesnt idle right now and it has trouble starting. The comression was tested and is great, the filter is clean, carb is clean etc. I cant find the idle speed jet to adjust the idle higher. I messed witht he pilot air screw for a second or two but I cant really figure anything out about the air screw or pilot jet size without getting it to idle. There is no idle speed jet that I can see and I was wondering if anyone can help me out. Also what plug does it need? Thanks!! I will pay back any good info by adding to your rep(gas tank)

Thanks

Phil

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I know at least on my bike 98 cr250 that the choke knob can be spinned to adjust the idle speed. sorry if im wrong

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Idle has always been a sore subject for me. In my opinion and a lot of folks I know that race or used to race, a bike like the 250 should not idle. But that is just our humble opinion. I know that this does not offer any helpful advice and I am sorry for that. But the idle should come from the right hand. Idling these "race" bikes sets up for fouled plugs and buildup on the top end. Atleast that is what I have seen. As far as I know there is no idle jet on a 250. But I have not seen or worked on a carb any older than a 97. The only thing that I could think of that would help is playing with the needle and airscrew.

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Okay well every racing 2 stroke I have ever owned has idled perfectly. Maybe old 250's dont...maybe they do.. I'll have to figure it out for myself. I'll keep you guys posted.

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These jetting specifications are designed as a rule of thumb. They are in no way absolute. Variations in air density, specific gravity of fuel, altitude and other engine modifications play a large part in jetting. It is the responsibility of the owner to determine proper jetting for their engine.

HOW TO JET - THE BASICS

Plug reading doesn’t work. Revving the engine while it’s sitting in the garage doesn’t work. Other than Dyno testing, the steps below are the only way you can consistently jet your engine.

1. Find a gentle slope that you can ride in 2nd or 3rd gear. Look for something that will put a decent load on the engine. This will be your tuning test area.

2. Make the recommended jetting changes. Always start rich and work leaner.

3. A basic outline of which jet is active at a particular throttle setting:

Pilot Jet = 0 to 1/4 throttle. Needle = 1/4 to 3/4 throttle. Main Jet = 3/4 to Full Throttle.

● Changing the Main Jet size won’t affect how your engine idles or runs at 1/4 throttle.

● Engine RPM isn’t what determines which jet is active - only throttle position does this.

4. Start and warm up the engine, then ride your ‘test hill’. Any point where you feel the engine stumble or hesitate indicates a rich condition. Note the throttle position and modify the corresponding jet (1/4 to 1/2 throttle = leaner needle. 3/4 throttle or more = leaner main jet).

5. Only change jetting by 1 step at a time, and 1 circuit at a time (don’t change needle and main at the same time). Re-check after every change.

6. Once the engine runs smoothly throughout, you’re jetted!

If you ever notice an abrupt change loss of power, or engine sounds changes, shut it down.

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I know at least on my bike 98 cr250 that the choke knob can be spinned to adjust the idle speed. sorry if im wrong

I'm with you. all the crs I've worked on have either the screw to lift the slid, or the choke knob turns to raise and lower idle. If it's on the choke knob, you can unscrew the knob at the base and pull out the whole assembly in one piece. (it has a needle at the end that goes into a jet).I just had a friends cr500 (with that carb) that was very eratic. I found that at the bottom of that choke/ idle assembly, there is a needle and jet but, the jet was not the screw in type, it was pressed in and had come out of the hole. I had to swell the brass jet and tap it back in.

Also, 2-strokes should be able to idle. Mine idle great. you just don't want to idle them for long because they "load up". if they don't, something is wrong like carb, air leak in boot, leak in crank seals, low compression, gaskets etc.

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I personally don't like and never have let mine idle. To each his own I guess. If you like it to idle then make it idle. Every mechanic that I know that runs and preps race bikes does not have a two stroke that idles. Don't take this as picking a bone with you t-roy. Just my couple pennies worth.

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Well I have never heard this and I'm curious. All of my 2 strokes idle and I let them idle for very long periods of time without fouling plug, smoking, bogging once throttle is opened etc. Several of the bikes were professionally jetted.

Assuming the bike is idling with no problems, is there any advantage with a carb jetted so that it will NOT idle? Do you jet it too rich or too lean to do this? Explain it to me and I will try it out!

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There is no particular advantage, other than you dont have to worry about fouled plugs, less carbon build up in the cylinder. A lot of these things can be traced to type of oil used in premix and gasoline used also. So there are a lot of variables. If you are happy with you jetting and the idling of you bikes then stick with it. It sounds like you have had good guys do it for you and it is working so no reason to change it. This more like one of those things that you see in "What oil to use" threads. There is not particular right or wrong way. Personal preference.

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Well I have never heard this and I'm curious. All of my 2 strokes idle and I let them idle for very long periods of time without fouling plug, smoking, bogging once throttle is opened etc. Several of the bikes were professionally jetted.

Assuming the bike is idling with no problems, is there any advantage with a carb jetted so that it will NOT idle? Do you jet it too rich or too lean to do this? Explain it to me and I will try it out!

That's good jetting. 👍 IMO. If the jetting is right, and no air leaks. it should idle but, I would not let it sit idling for too long because there is no air moving across the radiators.

Pugnasty, I'm not saying that you should let it idle. I'm just saying it should be able to idle IMO.:worthy:

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I have always had mine set to just below able to idle. I would rather it die than have it running on idle. It is not a problem to me to just keep blipping it or let shut down. But hey, to each his own.

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A friend just got an 89 Cr250 and I told him I would perfect the jetting. It doesnt idle right now and it has trouble starting. The comression was tested and is great, the filter is clean, carb is clean etc. I cant find the idle speed jet to adjust the idle higher. I messed witht he pilot air screw for a second or two but I cant really figure anything out about the air screw or pilot jet size without getting it to idle. There is no idle speed jet that I can see and I was wondering if anyone can help me out. Also what plug does it need? Thanks!! I will pay back any good info by adding to your rep(gas tank)

Thanks

Phil

OK, well the choke knob IS the idle speed adjuster. I also have an 89 CR250 and I had to adjust the idle also. As for the plug question, the stock plug is a BR9ES (from NGK?)

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don't you get the most performance out of the bike if it doesn't really idle?

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i also have an 89 cr250, and yes the idle is on the choke, but i have never gotten mine to idle no matter how much i turn the choke. Id rather not idle though, she already eats up enough fuel. And i run a BR8EG which is what the book calls for i believe, the BR9ES Will also work.

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the reason racers set theire 2-strokes up with no idle is to compensate for the lack of engine braking, 2-strokes produce very little engine braking and by basicly killing the engine everytime you let go of the gas you create more drag on the rear wheel, it's "pretend" engine braking...

every 2 stroke that's healthy should be able to idle, and unless you race there is no reason to not let it idle either, a properly jetted bike WILL NOT foul plugs just because they idle for 10 secs or so, that's just a myth. there is no other gains from having a bike that does not idle, if you ride offroad it's just a pain to have to keep blipping the throttle in order to keep the bike alive.

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