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Help with yz250

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I just picked up a 2001 yz250 yesterday. It cranks first kick cold with no choke and sounds great. But when I ride it, something isn't quite right.

It will rev all day in neutral, and in first gear, but when I get in second and up it doesn't want to rev out all the way. It sounds like it's hitting a rev limiter around 3/4 throttle and it just doesn't have that "scary fast" power band that everyone has warned me about.

If I ease into it in second it will hit about half the time.

Here's what I've done so far: case oil change, spark plug cap, spark plug, air filter, new gas (he was running 50:1, I changed over to between 32:1 and 40:1).

The previous owner said it "may" have a flywheel weight on it, which I thought would tame the transition some but not kill the top end. Also it has a full pro circuit pipe on it and he said he thinks it hasn't been jetted.

I was just wondering if anyone else has run into this problem and has a quick fix solution or any ideas. When I checked the old plug it seemed rich, but when I swapped plugs it didn't look as bad so I'm not sure if it is or not. I haven't yet looked at the jets to see what's in it, like I said I've only had the bike 24 hours. I didn't know if jetting would kill the top end or not, I haven't really ever messed with two bangers and I've never put a pipe on a bike so jetting was never an issue for me.

Any help is appreciated!

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Start with jetting.  First kick with no choke on a 2 stroke is usually signs that it is way rich.

 

Jetting has to be right before you can troubleshoot other things.....  If jetting doesn't work, at least going through the process can give hints at what the issue may be.

 

Reasons why you should start with jetting:

 

Start easy without choke, not always, but usually a good sign it needs jetted.

Different fuel

Different pipe

Prev owner didn't think it was jetted.

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I just posted this in general discussion, sorry if you read it twice. I figured i may get better results from this forum.

I just picked up a 2001 yz250 yesterday. It cranks first kick cold with no choke and sounds great. But when I ride it, something isn't quite right.

It will rev all day in neutral, and in first gear, but when I get in second and up it doesn't want to rev out all the way. It sounds like it's hitting a rev limiter around 3/4 throttle and it just doesn't have that "scary fast" power band that everyone has warned me about.

If I ease into it in second it will hit about half the time.

Here's what I've done so far: case oil change, spark plug cap, spark plug, air filter, new gas (he was running 50:1, I changed over to between 32:1 and 40:1).

The previous owner said it "may" have a flywheel weight on it, which I thought would tame the transition some but not kill the top end. Also it has a full pro circuit pipe on it and he said he thinks it hasn't been jetted.

I was just wondering if anyone else has run into this problem and has a quick fix solution or any ideas. I'm hoping I can just jet it and fix it, but I didn't know if that was a symptom of needing jets or if I've got another problem on my hands. When I checked the old plug it seemed rich, but when I swapped plugs it didn't look as bad so I'm not sure if it is or not. I haven't yet looked at the jets to see what's in it, like I said I've only had the bike 24 hours.

I would love some input on what jets other people have had luck with. Like I said, I know it needs to be jetted I'm just afraid if I've got another problem and I start messing with the carb I could screw it up even worse.

Any help is appreciated!

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I just picked up a 2001 yz250 yesterday. It cranks first kick cold with no choke and sounds great. But when I ride it, something isn't quite right.

It will rev all day in neutral, and in first gear, but when I get in second and up it doesn't want to rev out all the way. It sounds like it's hitting a rev limiter around 3/4 throttle and it just doesn't have that "scary fast" power band that everyone has warned me about.

If I ease into it in second it will hit about half the time.

Here's what I've done so far: case oil change, spark plug cap, spark plug, air filter, new gas (he was running 50:1, I changed over to between 32:1 and 40:1).

The previous owner said it "may" have a flywheel weight on it, which I thought would tame the transition some but not kill the top end. Also it has a full pro circuit pipe on it and he said he thinks it hasn't been jetted.

I was just wondering if anyone else has run into this problem and has a quick fix solution or any ideas. When I checked the old plug it seemed rich, but when I swapped plugs it didn't look as bad so I'm not sure if it is or not. I haven't yet looked at the jets to see what's in it, like I said I've only had the bike 24 hours. I didn't know if jetting would kill the top end or not, I haven't really ever messed with two bangers and I've never put a pipe on a bike so jetting was never an issue for me.

Any help is appreciated!

Sounds like it'd rich on the pilot jet and lean on the main. How much compression does it have? Changing the mix ratio will effect your jetting slightly also.

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I haven't checked compression but it seems really high just from kicking. I'm comparing to a buddies 03 cr250 and my yz seems much harder to turn over.

Would anyone happen to have an idea of what jets to recommend for it?

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I haven't checked compression but it seems really high just from kicking. I'm comparing to a buddies 03 cr250 and my yz seems much harder to turn over.

Would anyone happen to have an idea of what jets to recommend for it?

If you don't have a manual look up your bike on TT parts and see what stock jetting and needle is . Start over from factory settings. 

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I just posted this in general discussion, sorry if you read it twice. I figured i may get better results from this forum.

I just picked up a 2001 yz250 yesterday. It cranks first kick cold with no choke and sounds great. But when I ride it, something isn't quite right.

It will rev all day in neutral, and in first gear, but when I get in second and up it doesn't want to rev out all the way. It sounds like it's hitting a rev limiter around 3/4 throttle and it just doesn't have that "scary fast" power band that everyone has warned me about.

If I ease into it in second it will hit about half the time.

Here's what I've done so far: case oil change, spark plug cap, spark plug, air filter, new gas (he was running 50:1, I changed over to between 32:1 and 40:1).

The previous owner said it "may" have a flywheel weight on it, which I thought would tame the transition some but not kill the top end. Also it has a full pro circuit pipe on it and he said he thinks it hasn't been jetted.

I was just wondering if anyone else has run into this problem and has a quick fix solution or any ideas. I'm hoping I can just jet it and fix it, but I didn't know if that was a symptom of needing jets or if I've got another problem on my hands. When I checked the old plug it seemed rich, but when I swapped plugs it didn't look as bad so I'm not sure if it is or not. I haven't yet looked at the jets to see what's in it, like I said I've only had the bike 24 hours.

I would love some input on what jets other people have had luck with. Like I said, I know it needs to be jetted I'm just afraid if I've got another problem and I start messing with the carb I could screw it up even worse.

Any help is appreciated!

 

It could be that the fuel filter is clogged / not letting enough fuel flow.  Pull the fuel line from the carb, and then see how it flows into a bottle.  It should flow pretty good if nothing is blocking it.  If it is trickling, pull the filter and see if it flows freely from the petcock.  If it is the filter, get one at an auto parts store. It could be the petcock too, but make sure you have the o-ring or gasket, etc. because the old one will probably be no good for re-use.  The next thing would be the carb.  Probably not affecting your issue, but how's the reeds? 

Edited by mch

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Jetting is an easy place to start. Stock is a 50 pilot, N3EJ 2nd or 3rd clip, 178 main.  Even with a pipe on it, it shouldnt be far off. Elevation makes a big difference too.

 

I feel like theres about 9 billion threads on this subject as well.

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Take powervalve out and make sure its operating smoothly. Maybe it isnt opening. That would cause it to fall flat. No power band could be a stuck pv, especially if its been run rich. It gums fairly quick depending on oil type and riding style.

Edited by dbart250
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Update:

Today I took a look under the hood, and found that the previous owner had the needle set to the very top slot (leanest) and a 190 main jet and the air screw 3 turns out. I'm trying to go all the way back to stock now with everything. I got the needle and air screw and it did much better around the neighborhood but still not 100%.

I'm going tomorrow to buy the stock main jet. I figure after I ride some with all the stock settings I can check the plug again and see if I'm rich or lean.

But I have had a few mentions of the power valve. How do I check to see if it is stuck or not? I've heard pull the pipe and look, but I've never messed with power valves before so I didn't know where to start

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Theres a cover you have to get off that covers the pv. Now, i have an older bike so its much simpler, but if you dont have a manual i would get one. I know everyone says that, but its worth the money, especially for this stuff. With that said, you should be able to move the pv by hand and see if it is gummy. If you pull the cover and its hard to tell whats what, it needs to be cleaned!

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I would take a look at the reeds too. Just to make sure they aren't damaged and are sealing well. I had a cr that felt like it was being held back, spent a lot of time playing with jetting before I decided to pull it down to investigate and as it happens, my reeds were shot. A new set saw me right.

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Look in the FAQ section at the top of the Yamaha 2 stroke section. There is detailed info on how to jet your bike and there. Read it and follow the instructions that is the only way to get it right. You can also get a free downloadable shop manual too, That is what I use.

My guess is proper jetting will fix your problem.

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