Jump to content

YZ250 jetting

Recommended Posts

To start off I found a killer deal on a 1999 yz250. 

So Its a 1999 YZ250 that i got for 50 bucks!! Bike is 100 percent complete and came with a paddle, a stand and a bunch of other stuff. Bike had been sitting since 2009 and was locked up.

So i got the bike home and took the top end off. Found out the wrist bearing has seized up and a couple other things were wrong with it. So i decided to do a full rebuild. New crank, New bearings, everything. I have done rebuilds like this before so no real problems up until now. Got the bike built and all good to go, fired it up, two kicks runs like a champ.

Got the bike all broke in and was ready to open it up and use full throttle and it just falls flat of its face on the top end. Pulls great through the rev range until it gets into the top end. My dad has been helping me with the carburetor issues because I am not to keen on carbs. He thinks that is doesn't have the right jets in it. I rebuilt the carb with the rest of the bike and it has the stock jet (170) in it. 

I live in Idaho at about 4200 feet. Does anybody have any suggestions on jets or ideas on what the problem with the bike could be? If so it would be greatly appreciated. 

Thank you all. 

Share this post


Link to post
Share on other sites

Oh I also didn't mention the plug looks good. It is not black or white it actually looks really good. so that also confuses me. 

Thanks again.

Share this post


Link to post
Share on other sites
1 minute ago, 2 STROKE YZ DOC said:

Good starting points:

170, 48, 2nd clip position, 40 leak jet, 1.5 turns out on the AS. 

168, 46, 3rd clip position. Same/same

 

What do you mean by clip position?? 

  • Like 1

Share this post


Link to post
Share on other sites

Your carb has a needle with clips, take the two bolts on top of the carb out and pull out the slide. That’s the piece that holds the needle attached to your throttle cable. Now that it’s out pull back your spring back on your cable and get it loose from the slide has a notch. Now that you got that out take 6mm and unscrew the bolt in the slide. Now your needle is out the blunt thick end is what you count down on your notches. Now put it on the 2nd clip and reverse steps good luck man.

Edited by Smokey450r
  • Like 2

Share this post


Link to post
Share on other sites

By “falling flat on it’s face” do you mean it bogs heavily or almost quits when you get into the top end?  If so it might be worth taking a good look at the power valve too.  I had issues with my 2005 this last year, where it would bog and almost quit once I got above about 1/2 throttle.  I messed with all kinds of jetting, air screw, etc to no avail.  Turned out I had worn parts in the power valve and it was sticking closed or not opening fully when the bike warmed up.  Once I replaced a few parts in the power valve and cleaned it thoroughly my problem went away.

  • Like 3

Share this post


Link to post
Share on other sites
10 hours ago, Chalk said:

By “falling flat on it’s face” do you mean it bogs heavily or almost quits when you get into the top end?  If so it might be worth taking a good look at the power valve too.  I had issues with my 2005 this last year, where it would bog and almost quit once I got above about 1/2 throttle.  I messed with all kinds of jetting, air screw, etc to no avail.  Turned out I had worn parts in the power valve and it was sticking closed or not opening fully when the bike warmed up.  Once I replaced a few parts in the power valve and cleaned it thoroughly my problem went away.

That has been a concern that has bounced around my head but when i rebuild the bike i set the cylinder off and had the power valve serviced at the same time. They replaced some parts and adjusted it. Not saying it couldn't be the problem just not sure how to tell if that is the case? Is there a clearance in there you can check or how to you make sure that everything is in spec?

Thank you all

Share this post


Link to post
Share on other sites
13 hours ago, 2 STROKE YZ DOC said:

Good starting points:

170, 48, 2nd clip position, 40 leak jet, 1.5 turns out on the AS. 

168, 46, 3rd clip position. Same/same

 

Okay Thank you again and sorry to ask another what feels like a dumb question. 

What is the "leak jet"?? I thought carbs only had two jets? Like I have said before I do not know much about carbs that is why i made this post....

And where is that jet??

Share this post


Link to post
Share on other sites

Read this whole thread beginning to end. 

D7ED771A-9E10-4744-B4F3-A55CF2145C08.thumb.jpeg.7505dd87b33cbdc34e88305b29b4426c.jpeg

#27 although your carb claims a 80 is stock. 

The 99 has been a bitch to jet 80% of the time and many just jump to a newer carb w/o connecting the TPS as your harness does not support one. 

After hours of jetting frustration, and cash for jets, the alternative is best. 

  • Like 1

Share this post


Link to post
Share on other sites
2 minutes ago, 2 STROKE YZ DOC said:

Read this whole thread beginning to end. 

D7ED771A-9E10-4744-B4F3-A55CF2145C08.thumb.jpeg.7505dd87b33cbdc34e88305b29b4426c.jpeg

#27 although your carb claims a 80 is stock. 

The 99 has been a bitch to jet 80% of the time and many just jump to a newer carb w/o connecting the TPS as your harness does not support one. 

After hours of jetting frustration, and cash for jets, the alternative is best. 

I have a carb for what i was told was a 2001. I looks identical other then it does not have the fuel cut solenoid valve or the hole for it. Would this be a better option?

Share this post


Link to post
Share on other sites
6 minutes ago, Ginger256 said:

I have a carb for what i was told was a 2001. I looks identical other then it does not have the fuel cut solenoid valve or the hole for it. Would this be a better option?

You could try it. Should have solenoid and TPS if it’s an 01. 

DC88F89E-6C02-4E06-BCAA-9871D5FEC55A.thumb.jpeg.9bf6e291239552f67c5c06c96b10bce9.jpeg

This is an 01

Share this post


Link to post
Share on other sites
16 minutes ago, 2 STROKE YZ DOC said:

You could try it. Should have solenoid and TPS if it’s an 01. 

DC88F89E-6C02-4E06-BCAA-9871D5FEC55A.thumb.jpeg.9bf6e291239552f67c5c06c96b10bce9.jpeg

This is an 01

Okay ya. I have no idea what carb that is. Ive look at 98-2002 and non of them are that carb. So who knows. 

Am i able to get that #40 jet just anywhere? Should be a pretty common thing? 

 

Share this post


Link to post
Share on other sites
1 hour ago, 2 STROKE YZ DOC said:

As common as a cold at a kehein dealer. 

UGGGGGGG local power sports place cant even get it. guess im waiting a couple days

1 hour ago, 2 STROKE YZ DOC said:

As common as a cold at a kehein dealer. 

UGGGGGGG local power sports place cant even get it. guess im waiting a couple days

Share this post


Link to post
Share on other sites

Well i couldn't get a 40 today but i had a 50 kicking around the garage and WOW. i set it to exactly what you said to haven't tweaked it at all and A WORLD OF DIFFERENCE!!!! Incredible, so going to order the 40 and see if it gets even better!!!

  • Like 2

Share this post


Link to post
Share on other sites

1999 YAMAHA YZ250 JETTING

Main jet: 172

Pilot jet: 50

Power jet: 80

Needle: N3VF

Clip position: 2nd from top

Air screw: 1-3/4 turns out (1 stock)

 

Share this post


Link to post
Share on other sites
2 hours ago, Ginger256 said:

Well i couldn't get a 40 today but i had a 50 kicking around the garage and WOW. i set it to exactly what you said to haven't tweaked it at all and A WORLD OF DIFFERENCE!!!! Incredible, so going to order the 40 and see if it gets even better!!!

SLC isn't terribly far and I know that Rockymountainatv is just past provo, depending on where you are in Idaho, you could be as little as 2 hours away.

  • Like 1

Share this post


Link to post
Share on other sites
3 hours ago, Ginger256 said:

Well i couldn't get a 40 today but i had a 50 kicking around the garage and WOW. i set it to exactly what you said to haven't tweaked it at all and A WORLD OF DIFFERENCE!!!! Incredible, so going to order the 40 and see if it gets even better!!!

Getting close makes a world of diff, but don’t go to far the other way. Keep us posted on your settings when you get it crisp. 

Share this post


Link to post
Share on other sites
2 hours ago, 2 STROKE YZ DOC said:

Getting close makes a world of diff, but don’t go to far the other way. Keep us posted on your settings when you get it crisp. 

I will definitely keep posting as I can. I am in the Air Force and go on a deployment next Tuesday so hopefully i can get it going good and get a ride on it before i leave!!!

Thank you for everyone's help. Very much appreciated.

  • Like 3

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Reply with:


×