dual carb advice and base gasket question

1 reply to this topic
  • martyxr6

Posted January 31, 2006 - 02:00 PM


I have an 85 xr600 that i split the cases on to replace a few gears (go figure) and I thought once I had it apart i would go through the top end. I got all excited about a 628 kit, but it needs to last me a couple more years and I hear mixed thoughts on reliability. So I have decided upon a 98mm wisco w/11:1 comp and a stage 1 hotcam to compliment the increased compression. I l have an unplugged stock exhaust and am wondering if any of you have experience on how much I will need to change the stock jetting or mess with the carb slide-opening-timing. Ideally I would have liked a 10:1 compression, but wiseco seems to be the best for the $$$. So my next question is.... Does anyone have any thoughts on using two cylinder base gaskets to drop the compression ratio? I omitted the base gasket on my old xl500r to increase the compression, so the reverse should also hold true, but I worry about two gaskets squishing to much over time. My gut tells me it's a bad idea, but maybe.....? I know that by using a cam with a longer exhaust duration helps keep cylinder pressure down as opposed to the stock cam, but I still wonder if 11:1 is too high. I ride a lot in 90deg weather with only 91ron available. Trying to retard the cam timing makes me feel queasey and would require buying all the necessary tools. Am I just overthinking all of this as usual. My eyes hurt form trying to find related posts. Thanks.

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  • timothypg

Posted January 31, 2006 - 03:25 PM


hi. i,ve got an 86 xr600r and i'am in the same boat as you. i had planned on a 628 up until the last couple day's. i have been playing with the carbs and i have gotten ALOT of extra power this way. mods, aftermarket exhaust (wileyco) got a screamin deal and it is great. drilled holes in the side's and cut open the top of the air box. went to 128 main jets, my air fuel srew is only open about 3/4 of a turn so i will probably look at changeing the slow jet's also. ground inside of header smooth, wrapped header to keep some of the heat in the ex. and of the engine. (it has helped) expensive though $2.00 a foot. left the needle alone. these mods have made a BIG difference. i thought about high comp. piston but then you have to deal with more heat and less reliability in my opinoin. i personaly would not double up the gaskets. with these mods i have to be careful going into 2nd (front end comes up fast) :thumbsup: 3rd comes up easily as well, might be able to get 4th if i try. so these are some of the things i have done and i'am very pleased. let me know if you have anything. tim :thumbsup:

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