496 replies to this topic

[BDubb106 TT Addict]

RCannon said:

JD had me buy a current (99-12) yz250 jet kit for my 97 and it worked well. As far as the exhaust port mark on the piston, make sure the powervalve is not touching it. Also, once your in this far, match the open powervalve to the exhaust port. Match it PERFECTLY in the fully open position. The top end power gain is huge. The metal is so soft that its really easy to hand file or emery cloth away the imperfections.

How will I know where to start if I get the current kit? Are the jets similar or will I need to cross reference?

Could you elaborate on matching the PV a little? Im familiar with the new style PV but have no idea about the older ones. I have them removed at the moment, soaking in carb cleaner because they were sooo carboned up Im surprised they even moved.

[adam728 TT Addict]

ftball90 said:

Piston... has quite a bit of blow by for 25-26 hrs. I ride the bike hard, but I dont think I ride hard enough to create this much blow by. Anything abnormal for 26 hrs on this top end? One thing I noticed about this piston is it was extremely noisy compared to normal.

Underside:

what can you guys tell me about my jetting by looking at the plug and the piston. Seems like Im rich on one end and lean on the other??? Also IDK what those scuffs are from, not typical cold seize marks. At least none Ive seen.

Running quite lean. There's no wash on the top of your piston, and that colored spot under the crown is huge, meaning it gets hot when you are on the throttle.

Here's what my last top end after 56 hrs. I was happy to find it looking like this.






It's hard to tell, but those reeds look like they have some chipping in the 1st shot. Camera tricks, are are they damaged? If they are chipping, they are junk.

[BDubb106 TT Addict]

Thanks Adam. The reeds are chipped slightly but theyve been that way since I bought the bike. They are still sealed tightly, and only have that one small chip in the corner which is visible in the first pic. Just havnt thought about them again till now since this isnt my primary bike, not close.

As far as the top end... this bike has been rather difficult to jet, its like I keep going in circles. When I first got it, the thing was running 10x too rich on the main and 10x too lean on the pilot giving me lean surges. I richened the needle by one clip pos. and dropped the main 2 sizes and raised the pilot 3. When I did the plug chops they looked to be near perfect, but maybe I did something wrong durring my tests.

Oh well, sounds like the JD kit will be well worth the cash if it clears this issue up.

[GMO397 TT Diamond Member]

ftball90 said:

As far as the top end... this bike has been rather difficult to jet, its like I keep going in circles. When I first got it, the thing was running 10x too rich on the main and 10x too lean on the pilot giving me lean surges. I richened the needle by one clip pos. and dropped the main 2 sizes and raised the pilot 3. When I did the plug chops they looked to be near perfect, but maybe I did something wrong durring my tests.

Honestly, I can't jet a bike off plug readings using pump gas. When I get the perfect plug color it feels and sounds lean to me.
The best way I have learned to jet is to just do it by feel. I found out what rich and lean felt like and went from there.

Here's a shot of my piston, richer than Adam's, but still safe.
The plug on this piston was WHITE, it had me scared of what I was going to find when I pulled the head. I had a JD jet kit on my CR, never though much of it. Now that I'm more savy with my jetting, I want to give it a try and see if it can clean up the transitions. I'm looking forward to your review.

[RCannon]

To match up the powervalve, fit it back into the cylinder. Open it all the way. Look through the exhaust port and notice how it does not match. Mark the areas where it does not match, or the overhang, with a sharpie poked through the exhaust port. Remove valve and sand down the spots that overhang. A dremel is perfect for the job, but you could use emery paper if need be.Also match the two halves of the pv to each other. Its not as if there is an extra 5mm of material anywhere, but 1-2mm is normal. Sometimes the edge of the pv is too far back to overhang. I just ignored this. The air is traveling fast goign out of the exhanst port. Any mis-match is a big deal. Especially on a bike not known for top end power.

Notice how the open pv becomes the top of the exhaust port. You can polish this edge and carbon build up will be much less.

I have no idea if any of this applies to the new yz 250, but that older engine came alive on top end power (compared to stock) after doing this. I wish I had some pics as the description is a thousand times more complicated than real life.

[BDubb106 TT Addict]

GMO397 said:

Honestly, I can't jet a bike off plug readings using pump gas. When I get the perfect plug color it feels and sounds lean to me.
The best way I have learned to jet is to just do it by feel. I found out what rich and lean felt like and went from there.

Here's a shot of my piston, richer than Adam's, but still safe.
The plug on this piston was WHITE, it had me scared of what I was going to find when I pulled the head. I had a JD jet kit on my CR, never though much of it. Now that I'm more savy with my jetting, I want to give it a try and see if it can clean up the transitions. I'm looking forward to your review.

Thanks for this! This is the only bike that I own that I run straight pump in. All my other Yz's and F's run 50/50 pump/110 race fuel so maybe thats enough to throw my jetting knowledge off. I just dont see the need to run any race fuel in this bike since it runs as good as its going to get on anything combustible. Hence why Im getting the JD kit. Ill be sure to post up a review of how things unravel once I get my kit.

RCannon said:

To match up the powervalve, fit it back into the cylinder. Open it all the way. Look through the exhaust port and notice how it does not match. Mark the areas where it does not match, or the overhang, with a sharpie poked through the exhaust port. Remove valve and sand down the spots that overhang. A dremel is perfect for the job, but you could use emery paper if need be.Also match the two halves of the pv to each other. Its not as if there is an extra 5mm of material anywhere, but 1-2mm is normal. Sometimes the edge of the pv is too far back to overhang. I just ignored this. The air is traveling fast goign out of the exhanst port. Any mis-match is a big deal. Especially on a bike not known for top end power.

Notice how the open pv becomes the top of the exhaust port. You can polish this edge and carbon build up will be much less.

I have no idea if any of this applies to the new yz 250, but that older engine came alive on top end power (compared to stock) after doing this. I wish I had some pics as the description is a thousand times more complicated than real life.

yea Im pretty much lost. I think I get the concept but dont understand what Im supposed to take away. If I took pics of the PV do you think it would be easier to explain? Maybe you could mark the pics with paint or something? I just dont wanna screw them up. If that wont work Ill just give it a shot and pray for the best lol.

[tim512 TT Bronze Member]

RCannon said:

To match up the powervalve, fit it back into the cylinder. Open it all the way. Look through the exhaust port and notice how it does not match. Mark the areas where it does not match, or the overhang, with a sharpie poked through the exhaust port. Remove valve and sand down the spots that overhang. A dremel is perfect for the job, but you could use emery paper if need be.Also match the two halves of the pv to each other. Its not as if there is an extra 5mm of material anywhere, but 1-2mm is normal. Sometimes the edge of the pv is too far back to overhang. I just ignored this. The air is traveling fast goign out of the exhanst port. Any mis-match is a big deal. Especially on a bike not known for top end power.

Notice how the open pv becomes the top of the exhaust port. You can polish this edge and carbon build up will be much less.

I have no idea if any of this applies to the new yz 250, but that older engine came alive on top end power (compared to stock) after doing this. I wish I had some pics as the description is a thousand times more complicated than real life.

I think I understood your explanation, on my next topend I'll take a look and see what I can do :)

[tim512 TT Bronze Member]

GMO397 said:

Honestly, I can't jet a bike off plug readings using pump gas. When I get the perfect plug color it feels and sounds lean to me.
The best way I have learned to jet is to just do it by feel. I found out what rich and lean felt like and went from there.
[/IMG]

GMO, for the benefit of those who are currently trying to perfect their jetting but are very inexperienced (ie me) at what lean and rich actually feels like (beyond super obvious like a massive bog) can you please elaborate?

[RCannon]

If you take a pic of the powervalve, in the opened position, I'll try to explain. Aim the camera right down the exhaust port.

As a start, put the powervalve back together outside of the cylinder. Notice how the two pieces dont match up? Make them match and it will help a lot. Usually th eright side is slightly thicker than the left..by a mm or so.

[BDubb106 TT Addict]

Ok I get what your saying now... take the excess material off the one that is larger, in short, so they match perfectly.

Do you have to match the PV with the port as well? Thats where my confusion was. I thought that is what you were referring to.

Im still gonna take pics to for a little confirmation though.

[BDubb106 TT Addict]

RCannon said:

If you take a pic of the powervalve, in the opened position, I'll try to explain. Aim the camera right down the exhaust port.

As a start, put the powervalve back together outside of the cylinder. Notice how the two pieces dont match up? Make them match and it will help a lot. Usually th eright side is slightly thicker than the left..by a mm or so.

Once I put the PV back into the cylinder I saw exactly what you were talking about, the right valve was about 1.5 mm larger than the other all the way around. appx 1mm on the flat side (open), and .5mm all the way around on the rounded edge (closed). I evened the whole thing up so that they match perectly all the way around and match the port perfectly.

Snapped some pics of the work, dont know how well you will be able to tell from the pics because it was hard to get the correct angle so you could see that they lined up perfectly but here is what I got.

Pv cleaned up and matched.



Inserted into the cylinder.



These are the closest ones I got to getting a straight on shot.




It was rather easy to get them close with the dremmel, I then took a peice of fine sand paper and cleaned them up so they were perfect and smooth, next will be to polish them so the carbon doesnt stick to them as easily. Thanks for all your help Roland:thumbsup:

[BDubb106 TT Addict]

GMO397 said:

I think that cylinder looks dirty!!! hard to give much advice, clean it up and post some pics. If you've got a new cylinder already, I'd just keep that as a spare and get it replated later, use that cash to make it a sweet bike now!

Hey man took some pics of the cylinder all cleaned up, I noticed that there are some scuffs at the bottom on the intake side. Also looked closer at the piston and there are marks are on the intake side as well. Im guessing some dirt got past the filter and roughed it up a little.

However plating looks great and cross hatching is still very visible all the way throughout.




I think Im gonna go ahead and get it replated anyways. Something about it just worries me. IDK if it was the piston or the cylinder but that thing sure was noisy throughout that top end. Then it can sit there as a spare.:thumbsup:

Edit: it still looks dirty in these pics... I washed that thing 3 times and wiped it out with a "lint free" rag. Guess it wasnt so clean after all.

Edited by ftball90, 18 December 2011 - 07:40 AM.

[BDubb106 TT Addict]

I also got around to checking the crank out today, 100% perfect. Not the least bit of up and down play and only 1.6mm of side to side play which is well within the recommendation range in the manual.

Ill also be changing my ratio from 40:1 to 32:1. After a great write up by Chokey I decided to measure the oil pool in the bottom of the crank. It was non existant. I knew I was riding the bike hard but didnt realize I was riding it that hard. Kinda had me worried as he brought up that Amsoil Dominator doesnt have any additives to protect against rust and corrosion like alot of other oils do so its of upmost imporance to make sure that the rest of the motor (crank) is getting enough oil. He said the pool should be between 1/4-1/2 inch deep. Mine was dry. I was happy to see that there was no rust or corrosion but there was not a drop of oil under the crank.

[GMO397 TT Diamond Member]

ftball90 said:

I also got around to checking the crank out today, 100% perfect. Not the least bit of up and down play and only 1.6mm of side to side play which is well within the recommendation range in the manual.

Ill also be changing my ratio from 40:1 to 32:1. After a great write up by Chokey I decided to measure the oil pool in the bottom of the crank. It was non existant. I knew I was riding the bike hard but didnt realize I was riding it that hard. Kinda had me worried as he brought up that Amsoil Dominator doesnt have any additives to protect against rust and corrosion like alot of other oils do so its of upmost imporance to make sure that the rest of the motor (crank) is getting enough oil. He said the pool should be between 1/4-1/2 inch deep. Mine was dry. I was happy to see that there was no rust or corrosion but there was not a drop of oil under the crank.

My crank lobes looked way dirtier than that w/ only 40 hours and 927. Looks good in there!

I didn't have a pool in mine either, and I run 32:1. I'm going to try 28:1-24:1, can't hurt anything and it's great for peace of mind.

Have you mocked up the 98 cylinder to your bottom end yet?

[FIVEWIDE TT Gold Member]

Same turnout gear same harbor freight tools and stand, almost same bike in the same condition on the same stage of my build....you have all the symptoms of my disease...there is no cure.

[RCannon]

ftball, that looks really good. Its amazing to me to feel how much a slight mis-match made here in top end power. I think you'll be happy with the result.

[BDubb106 TT Addict]

GMO397 said:

My crank lobes looked way dirtier than that w/ only 40 hours and 927. Looks good in there!

I didn't have a pool in mine either, and I run 32:1. I'm going to try 28:1-24:1, can't hurt anything and it's great for peace of mind.

Have you mocked up the 98 cylinder to your bottom end yet?

No Im still waiting on it. Got all the parts from a seller on ebay so Im still waiting for them to arrive. As soon as I get it I will be sure to post pics of how everything works out.

RCannon said:

ftball, that looks really good. Its amazing to me to feel how much a slight mis-match made here in top end power. I think you'll be happy with the result.

I hope so... I was rather amazed at how soft that material was. Quite a bit of material had to be taken off to match them to the port. Why does Yamaha not clean these things up a little better? Im gonna take a look at the valves on my 03 and 08 as well to see if they are off as well.

[BDubb106 TT Addict]

FIVEWIDE said:

Same turnout gear same harbor freight tools and stand, almost same bike in the same condition on the same stage of my build....you have all the symptoms of my disease...there is no cure.

Lol I dont want a cure... I love it, not many people can say they love thier job, and have as much fun doing it as I can.

perfect job and perfect hobby. I just cant get enough of either.

[RHanson94 TT Bronze Member]

ftball90 said:

lol it sucks... takes forever to copy image codes from photobucket

You may have figured this out already but in photobucket, you can select all the pics you want and then down at the bottom there is an option under the "choose action" button to generate the image codes of everything you've checked. It'll show the list of them and then all you have to do is copy and paste. If you want them in a particular order, you have to make sure you have them organized that way in your album.

[BDubb106 TT Addict]

Anyone know what I can use to clean the cylinder studs?

Mine are extremely corroded. Or if they can be replaced I might just do that.