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Yamaha Tech Originally the Yamaha XT600 Tech Forum, due to demand it now includes all Yamaha's technical / mechanical / repair / preparation questions.
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  #1  
Old 4 Jul 2013
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Has anyone put in a 11.5:1 piston?

If any one has done the high compression up grade , how does it work. Stock cam or after market. How about heat issues? I would like to put one in but would like to know about pros and cons from someone who has done it. thumpthump
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  #2  
Old 4 Jul 2013
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I have a kit piston( wiseco), cam upgrade, springs upgrade. I havent used it because its better to have engine for more years than have a little more power for a few years. It works fine but offcourse it do more wear on the rest of the engine parts. If you have done upgrade with new exhaust all the way, KN filter and bigger jets you dont need more power and if you do buy a KTM with 75bhp.
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  #3  
Old 4 Jul 2013
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I have a 86 and a 90 with a spare engine. I have gone to air pods , rejetted and raised the needles on both with after market exhausts. The 86 is set up for serious offroad and has more than enough power. However I have the 90 set up more for street and fire roads. I want more power on the 90. I was hoping to put a 11.5:1 piston and use the stock cam or maybe a stage one. I am a little concerned about heat. I was wondering about what kind of power improvement I could expect for my efforts. As for as a KTM too much money and besides Its more fun to beat the new bikes with my old 27 year old xt. thumpthump.
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Old 4 Jul 2013
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Hehe your not going to beat any KTM 75bhp with changing piston, what you get is alot more torque and more wheelies.
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  #5  
Old 4 Jul 2013
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Hard to use 75 hp in the North Carolina mountain trails. Mostly tight twists and few streights , a cliff on one side with bears at the bottom. But torque and wheelies sounds good. thumpthump
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  #6  
Old 6 Jul 2013
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Really? No one has put the 11.5:1 piston in their xt? OK , does anyone know someone who has that can comment? thumpthump
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  #7  
Old 6 Jul 2013
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hi try these

hi you could ask on xt600.de or you could contact kedo.de who sell
Item 31220: WISECO 11.5:1 Piston Kit, Complete, 95.00mm
hope this helps steve
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  #8  
Old 6 Jul 2013
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Thanks , But I can not read German and the computer says it translates but will not on the forum. I was looking for final user opinions not biased seller comments. Thumpthump.
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Old 6 Jul 2013
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Cant see why you should have a problem.

Theres an xt600 facebook group (its called "Yamaha XT-600"), a lot of guys inthere have have high comp pistons.
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  #10  
Old 7 Jul 2013
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Thanks, Ill check it out. thumpthump
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  #11  
Old 7 Jul 2013
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All the motors I've seen that someone put a high comp kit in(not XT's) have been pretty happy with them, some have had heat issues( an added oil cooler will be helpful), several didn't last as long as the stock setup, BUT, with that extra power they also beat the motor pretty hard so that's a consideration. Mostly as long as you take care of it, don't run it at 7000rpm "because it sounds cool", and be vigilant with maintenance, it should work out good. I personally would go with something like 10:1 or maybe 10.5:1 and not have to worry about fuel quality/octane as much and make up for it by a good port job and valves. To get the most out of the piston a better set of carbs (CR33's work good I here) will be in order.
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  #12  
Old 7 Jul 2013
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XT600 DUAL CR33 Carburetor Kit - Yamaha Dual-Sport - ThumperTalk

http://www.brspecialtuning.co.uk/keihin.htm

http://www.motorcycle-exhausts.co.uk...uct--4280.html

http://www.motorcycle-exhausts.co.uk...ct--15507.html

You really need to dig down in your wallet to buy these..

I have this one on my bike and it works great: http://www.motorcycle-exhausts.co.uk...uct--3595.html
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  #13  
Old 7 Jul 2013
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Thanks xtrock. I would rather go with less compression also. However the only way I have found to go 10:1 is to over bore to 98 from 95. This leaves me with no where to go without boring the cases in the future. Also, when I went to 96 overbore I had more vibration and a 98 would be worse. I have not seen any other compression options except 11.5:1 available in the US. If I can find a 88 and up jug for cheep I may go the 10:1. Yea, those carbs are nice but cost more than I paid for either xt I have. What do you think of the 250 ninja carb swap? Right now I have A pipe and am running Air pods. It has taken a while but I finally have figured how to jet for those and have got it running strong with no flat spots. What jet sizes do they give you in the jet kit? I am running first gen TT carbs with 130 and 135 mains with the needles all the way up. A super rich midrange is the secret to jetting for air pods. Without that air box I have a top end power surge that never existed stock. thumpthump
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  #14  
Old 7 Jul 2013
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It would be a shame to do but you could machine of some of the dome off the 11.5 piston to drop compression, that's if it has solid material underneath and not forged hollow to reduce weight. I do have a set of BSR33 Mikuni's from an '05 Raptor 660 that bolt right on the motor, needs some airbox to carb fab work. Just waiting for time to do the swap. They are easlily gotten off ebay for $150 to $200. You won't get the big performance gain like with the CR's but should work better than the stock things.
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  #15  
Old 7 Jul 2013
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whatever you do with your piston are you going to get the crank rebalanced? I don't have an xt but on other engines I'm familiar with a properly done crank balance allowing higher revs with less vibration is a better performance improvement than more displacement or higher comp. Of course best is all together. Is there an oil pump upgrade for the XT - good for extra heat dispersion and higher pressure in the shell bearings, compensating for some of the extra force put in by any power increase upgrades. Just a thought.
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