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Clint

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Reply with quote  #1 
Hey guys. Just wondering if i would need to do anything else to my engine after putting a wiseco high comp piston in its completely stock/ stock boar and i was concerned after reading alot of things on the net about running race fuel and stuff.. i run 98 octane fuel at the moment and was out on the weekend and thought it may have been lagging in power.its 6 hours in after the rebuild.. any suggestions would be appreciated thanks clint
TxOutlawRider

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Reply with quote  #2 
Hi Clint,
  I really am not that well versed in the Fuji motors, but in general the primary things that effect how much compression you can run is 1) Octane of the fuel youre using, 2)actual Cylinder pressure produced (primarily decided by camshaft choice and positions, compression ratio, and load placed on engine), 3) heat in the combustion area (primarily determined by engine temperature, intake air temp, combustion chamber shape and surface area, sometimes carbon deposits and air/fuel Mixture), 4) Spark advance - high combustion pressures create higher flame speeds and too much spark advance ignites the mixture too soon.  5) Time- if the piston is moving fast enough it doesn't have as much time for the air/fuel to spontaneously combust .

Soooo... with all that said, how high is the compression of the piston you're using?
  What cam are you using and is it installed advanced or retarded? 
  Do you have any type of aftermarket CDI?  They tend to use a little more spark advance and it comes in sooner- leading to problems in a high compression motor.
  Is youre cooling system working ok?  Cooler engine temps and cooler outside temps create cooler combustion temps...which helps with using higher compression.
  Also you might try richening up the fuel mixture some to combat higher combustion temperatures. 
  Last, are you really placing allot of load on the motor, like sand paddles, towing,  or "lugging" the motor?

All that said... I'm sure if you let us know what the compression ratio is for your piston, someone here has actual experience with it and can tell you what you can run.  
  Ive been running 12.5 to 1 on my KTM motored Outlaw with bigger camshaft on pump gas (91-93 octane) for years without any issues, but that doesn't mean it'll work like that on a Predator 500 with stock cam.

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distraction628

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Reply with quote  #3 
12.5 and under 91, 12.7 and up to 13.2 , 94+,  13.3 to 13.5, 98+, and 13.6 to 14.3 , 110. that has what I tested on the fuji motor, based on stock CDI. add  timing advancement, add octane.
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TxOutlawRider

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Reply with quote  #4 
Quote:
Originally Posted by distraction628
12.5 and under 91, 12.7 and up to 13.2 , 94+,  13.3 to 13.5, 98+, and 13.6 to 14.3 , 110. that has what I tested on the fuji motor, based on stock CDI. add  timing advancement, add octane.


This is where real world experience can really help others. 

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2007 Outlaw IRS

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Clint

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Reply with quote  #5 
Hey guys thanks for the feed back..well its a 12.5 comp ratio i was told and its stock cams standard cdi standard exhaust and stanard air box im pretty sure the cooling system is working well i flush it and put new fluid in every year or so and us 98 pump fuel..with my riding i do alot of trails no sand paddels or sand and the temps in Australia get pretty hot somtimes so im a bit stumped cause when i 1st rebuit it it went really well i thought it felt better than stock but i took the beast out on a hot weekend and it felt like it went well for about 20 mins then may have lost a little power i did notice it was getting hot if that helps??
Clint

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Reply with quote  #6 
Hey guys thanks for the feed back..well its a 12.5 comp ratio i was told and its stock cams standard cdi standard exhaust and stanard air box im pretty sure the cooling system is working well i flush it and put new fluid in every year or so and us 98 pump fuel..with my riding i do alot of trails no sand paddels or sand and the temps in Australia get pretty hot somtimes so im a bit stumped cause when i 1st rebuit it it went really well i thought it felt better than stock but i took the beast out on a hot weekend and it felt like it went well for about 20 mins then may have lost a little power i did notice it was getting hot if that helps??
Clint

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Reply with quote  #7 
Also with it getting hot the temperature light didnt come on i just noticed it around my legs the temp light is working fine.just not sure on what to do is it worth rebuilding it again back to a standard piston or a 11.1 comp piston or just adding more after market parts to it but then will it be reliable and how much more power will i get? The stock air box i like with the 2 stage filter cause the trails i ride with friends normally get pretty dusty and that set up works well as i dont know anyone who runs a k n filter in theres??
distraction628

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Reply with quote  #8 
Ok first off, stock exhaust isn't a good choice with 12.5 compression. The stock air box  is fine with a good filter. But you can make improvements .  The power loss after 20 minutes could be a lot of things.  But it sounds like you need to re-jet the carb. As the motor gets to operating temps, it's needs for fuel changes. Heat your feeling, I assume off the header,  usually indicates lean on the needle and main.  I would start by going up 2 full main jets and moving the needle clip towards the  fine tip end two slots.. Then adjust as needed. Or put on a dyno and have a shop tune it.

I would fine a better exhaust , such as a good slip on, like Aaen, HMF, Pure Polaris, etc.  They also will require re-jetting.

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Clint

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Reply with quote  #9 
Cool thanks heeps for the information ill definitely be doing this as i wanted to put a hmf slip on pipe for a while now.but with jeting the carby is there any jets you could recommend as im not sure on what my best option would be or the size of the jets i dont even know what size the stock jets are?
Clint

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Reply with quote  #10 
Also is there a certain size jets i should buy and should i get the whole kit or just the jets? Thanks
distraction628

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Reply with quote  #11 
Stock  main is 150, pilot is 45
Get a 48 pilot, 155, 157.5, 160,,162.5, 165 , 167.5mains. Start with the 167.5main and the 48 pilot with the mix screw at 1 3/4 turns out and adjust for best idle at 1800 rpms. and see how it is, then  go down one main  jet at a time. Start doing full throttle runs in 4th gear. see what one gives you  the best pull.  That is a short version. there is tons of info on here how to jet it well.  Using a a/f gauge is best or time on a dyno.

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07 525, 06 500, 10 525s 09 RZRs, 04 Ram 2500 Cummins 6spd, 08 Fuzion toy-hauler
Clint

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Reply with quote  #12 
Awesome thanks for the information dude that will help me alot thank you.also do you recommend any brand to go for with the jetting kit?
Clint

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Reply with quote  #13 
Ive seen stage 1,2s,3s jet kits is this what i should be looking at?
distraction628

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Reply with quote  #14 
Ok some like jet kits like dyno jet.  I do not!!! I would not but a jet kit. I would just buy the jet sizes I listed. from a good place such as jet-r-us/ or a dealer, now jets r us does have a jet kit , really there just selling you a bunch of main jets not a kit with a needle .  http://www.jetsrus.com/a_jet_kit_atv/polaris_500_predator_2003-2007.htm



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07 525, 06 500, 10 525s 09 RZRs, 04 Ram 2500 Cummins 6spd, 08 Fuzion toy-hauler
Clint

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Reply with quote  #15 
Awesome thanks so much for this information dude ill get ordering this straight away without this site i would be lost thanks again..can i get the 48 pilot on this site aswell?
distraction628

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Reply with quote  #16 
Yes they have every jet you need.
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07 525, 06 500, 10 525s 09 RZRs, 04 Ram 2500 Cummins 6spd, 08 Fuzion toy-hauler
Clint

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Reply with quote  #17 
Thanks alot dude 🤘😎🤘
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