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05 & 06 Yz250 Pipe Mod

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current bike for this mod and testing- 06 YZ250, stock silencer and motor, jetted for Florida with a mix of race/pump fuel.

I have two stock pipes at the moment, one is a 06 and the other is a 05. As some might know the 06 (and 07) pipe is slightly different than the 05 pipe in that the 06 pipe's head is 2mm longer... (well actually the part of the pipe that connects to the cylinder is welded on the rest of the pipe 2mm further out in 06). This is what made the 06 bike feel torqier and crisper Vs the 05. Both the 05 and the 06/07 pipes have the same part numbers but they are different and Yamaha even said it had a new exhaust when they released the 06.

So I built a spacer for the 05 pipe to slide into the pipes head and pull the pipe 1/8" outward away from the exhaust port. This is very close to the 2mm that was added in 06 so I assumed it would perform like a 06. I was wrong....

What I stumbled into was a great combo or mod.

For comparison 06 pipe pulls strong and crisp from the bottom, yanks firmly through the middle and signs off slowly but sometimes early in the top-end. The 05 pipe (without the spacer) pull strong off the bottom (but not as strong as the 06), yanks firmly through the middle and revs out further throughout the top, but overall doesnt feel as crisp as the 06 pipe.

Now, the 05 pipe with the 1/8" spacer added.........

On startup it is instantly noticeable that something is different, on the stand the engine is much sharper and crisper, throttle is touchier and it sounds hyperactive. You can actually hear much more pinging (that sharp 2 stroke sound) going on inside the pipe. On the track the bike has a sharper throttle responce at any RPM and always follows with a rush of pull. The throttle cracks open sharper than the 06 pipe and then follows with same torque and bottom end as the 06. The mid range output seems to be the same however it sounds crisper and cleaner and feels somewhat snappier if punched while in that range. Heres the real improvement, the bike actually has a real top-end. Usually exhaust spacers give up some top for more bottom and thats why Im confused. The top-end is a rush that yanks the bike forward more than the strong mid range ever did. The bike seems to get me to the face of the jump much easier and much faster, going 3rd,4th & 5th is just plain faster and the bike sings a strong note while doing it. It will also pull through deeper power robbing sand better, and the improved top-end is always only a clutch stab away.

Of course I tried (back to back) the 06 pipe again and the 05 pipe without the spacer again and then it was final... The 05 with the spacer was the setup for me.

Brings the question... if the 06 pipe's only differnce from the 05 is its head being extended 2mm then why does the 05 with a spacer perform better than the 06? I could only think that maybe since the rest of the 05 pipe wasnt formed for this extra head lenth (like the 06 was) that using the spacer also changes the pipes stinger lenth as the cylinder see's it. Thats all I could come up with.:applause:

My springer final thought.......

If you have a 05 YZ250 or a 05 YZ250 pipe this could be a good mod for you. If you have a 06/07 pipe, your doing good as-is because the 06 pipe is a great pipe, however the 05 with a spacer could be better if you need more get up and go and like a super crisp bike.

I think the only downside (for some people) to the 05 pipe with a spacer is the bike will act a little too hyperactive and quick on the draw for the guys that like a more mello powerband and massive flywheel weights.

Just a reminder of how sometimes its the little things that make the biggest difference.

Latter today or tomorrow I will try to get up some pics (on this thread) of the spacer and instructions on how I made mine (using a old aluminum skid plate for the material).

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Great Mod. I am anxious to try one on my bike.

Material sounds like no problem, but did you do anything special to cut out the inside portion of the spacer?

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Yes, great mod and thanks for posting. I have several 06 pipes in the garage, now I wish I had an 05 pipe hanging around.

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I was thinking about trying a thinner spacer..My son's RM 85 has a spacer in the exhaust.

If 2mm is the differeace on the 06 then that would be about a .080"(.0787") spacer..03937=1mm

But,if the 1/8" or.125 (3.17mm)which is only.046" diff.then that sounds like the thing to do.

I might try a couple of different thickness.

Thanks

Doug

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Yes, different thicknesses wouldnt hurt. I only tossed in one that was 1/8" thick because the skid plate that i used to cutout the spacer was 1/8" thick. I had planned to mill it down if the results were not as good. But with the results I gotten, I wont be changing a thing. Its good enough for me, for now.

Rcannon, I will grab a pic as soon as I can. Hopefully tomorrow.

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UpAllNight ,

Here's an idea.What about trying a spacer for the pro circuit works pipe,since its a mid-topend pipe.I would like to see the results.

Havent tried a PC... I dont even have a PC. All I have is 05 and 06 stockers.

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Maybe the factory didn't do this to the 06 pipe because it sounds like this may cause a lot more pinging on pump gas. Thats ok with me though I run the good stuff. So does anyone have an 05 pipe they would be willing to sell me?

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Maybe the factory didn't do this to the 06 pipe because it sounds like this may cause a lot more pinging on pump gas. Thats ok with me though I run the good stuff. So does anyone have an 05 pipe they would be willing to sell me?

What I ment when I said it made more of a pinging sound was that it sounded sharper in the pipe... I wasnt referring to pre ignition or spark knock.

I run a race/pump mixture and didnt really notice any issues.

I also wondered why Yamaha didnt use this pipe profile on the stocker. The only thing I could think of was they wanted a more rider friendly powerband.

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What I ment when I said it made more of a pinging sound was that it sounded sharper in the pipe... I wasnt referring to pre ignition or spark knock.

I run a race/pump mixture and didnt really notice any issues.

I also wondered why Yamaha didnt use this pipe profile on the stocker. The only thing I could think of was they wanted a more rider friendly powerband.

Ya I know what you are talking about it just sounds a lot more crisp and like it has some higher compression. I was just thinking maybe they experimented with this and it caused too much pre detonation on pump fuel. Did you try the 06 pipe with a spacer or maybe even the 06 with a .075" spacer would be the same? I am a machinist so maybe I'll do some experimenting with some different sizes on the pro circuit pipe, since I don't even have a stock pipe.

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You know, I should have tried the 06 with the spacer just to see. Let us know what it does with the PC pipe.

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Any chance this pipe mod could raise the exhaust port temp to levels that would begin to do damage?

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Any chance this pipe mod could raise the exhaust port temp to levels that would begin to do damage?

I used this on two track so far... and one of the tracks has a part where I go from 2nd all the way to the end of 5th WFO in deep same twice a lap. No problems yet.

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Have you pulled the head to take a look at the top of the piston, or looked up into the exhaust port with a light to check out the top-edge of the piston? Just wondering.

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No I havent... Im almost sure it will be ok though. I have used pipe spaces in various bikes since like 1997 and never had any failure due to one.

On the flip side... on 125's we use to shave off some of the pipes flange to bring the head closer to the cylinder, this would give the bike a stronger top-end. In some cases this would make a crappy 90's stock pipe feel just as good as some of the better aftermarket pipes of that time.

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If you ever have time, try pulling out the intake spacer. I think it may give you more of what you like in this bike.

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On that website RCannon posted there are 2 different styles of spacers. One that goes in front of the exhaust flange, and one that goes behind. Where exactly did you put your spacer?

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Have you pulled the head to take a look at the top of the piston, or looked up into the exhaust port with a light to check out the top-edge of the piston? Just wondering.

Ok I looked up into the exhaust port today... Piston looked as new as it is (been in there for about 2 months now). The head looked as good as normal as well.

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Ok here is some pics...

Picture013.jpg

Picture014.jpg

Picture015.jpg

Notice i cut the outside diameter to fit perfectly inside the flange of the pipe. And I also cut the inside diameter to just a hair larger than the inside diameter of the pipe. You dont want the spacer hanging into the exhaust flow, but on the same token you dont want a large open gap or space because you cutout the inside diameter too large.

I cut this out of a 1/8" thick old skid plate made out of aluminum. I used a compass (the one used to draw perfect circles) to help with making the circles. I cut it out using a jig saw and a blade for tight circles, then finished with a grinding stone on a drill to smoothen out the edges.

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