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  1. #1

    Cool Not Sure about clearanses..help

    97´ gp 1200 and i measure propeller clearanses.. top of the propeller it say 0.40 0.45 and 0.50 biggest clearanse is something like 0.55 manual says it should be something like 0.35 maximum. is that clearance big enought that i should do something or not? housing and prop looks good tought..

    Second, how much that stock cylinderhead is safe to lower to gain more cranking preasure? or is it worth of doeing at all?

    i only have slight porting and reeds+rideplate done, and it accelerates to max speed same as seadoo rxt.. well allmoust.. so light tuning is wellcome

    PLEASE, note that numbers i have given is millimeters.

    Thanks to everybody who will give answers This is very good site!


  2. #2
    Mpeavler's Avatar
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    Quote Originally Posted by Tontsa80 View Post
    97´ gp 1200 and i measure propeller clearanses.. top of the propeller it say 0.40 0.45 and 0.50 biggest clearanse is something like 0.55 manual says it should be something like 0.35 maximum. is that clearance big enought that i should do something or not? housing and prop looks good tought..

    Second, how much that stock cylinderhead is safe to lower to gain more cranking preasure? or is it worth of doeing at all?

    i only have slight porting and reeds+rideplate done, and it accelerates to max speed same as seadoo rxt.. well allmoust.. so light tuning is wellcome

    PLEASE, note that numbers i have given is millimeters.

    Thanks to everybody who will give answers This is very good site!

    The more spacing you have, the more thrust you will loose from the pump. You will need to replace the 155mm wear ring section. There are a few options....you can run stainless steel stock replacement and or buy the Delrin plastic replacement. Did you notice any burn marks on the prop? When the gap increases like it has you will have more cavitation then desired which again will impact all aspects of the efficency of the pump.


    You can run 155 PSI and still run fresh 93 octane gas. If you opt for higher compression, you will need to run a mix and or straight race fuel. Keep in mind that if you do opt for increasing the compression, send it to someone who is familar with a 2 stroke...ie Riva, Group K, Lowell, etc. Of course it's worth it....more compression gives more power in the low to mid range and will allow a bigger wheel to be spun giving more top end MPH.


    Mike

  3. #3
    DAGO RACING CREW 97GPSLEEPER's Avatar
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    Bump the compression up. If your exhaust ports have been ported, your compression is actually lower right now than stock. In smooth water you will beat an RXT once everything is dialed in.

  4. #4
    Mpeavler, i didnt see any burning marks there.. like i said the housing looks so good that i wonder if only new prop will do that thing? clearanses was so little out of specification. i know best results will come if change both..

    Iam quite familiar whit these 2 stroke engines, like tear down and put back together, but not even close pro mechanic when talking about "tuning"
    So thats why i was asking if that stock head has some measure that can take away to get better compression.. or does it have to reshape that "burning space"? looks like everybody has "riva" or something else cylinderhead.. even i have read that stock is good.. you got so much cheaper parts there

    I put here one site what i found, so you could tell me if you agree everything that have written on that site. http://uri.fi/gp1200mods/

    And the reason ive not so glad to do all like you guys said (like change housing and prop both) is that i live in finland and here everything is soooooo expensive.. and here is not so many guys where to sent cylinderhead to modify.. i still agree that when ones done right it doesent have to do second time hope you understand what i mean it is still good that you guys give all information how it is done "right" even if i try to save money now, iam quite sure that i do it Right ones, even if it cost a little more

  5. #5
    jdog800's Avatar
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    Just have someone deck your heads. Any machine shop can do this. For every .o10 thousandths you will gain roughly 10 psi. The stock squish is too big anyways so there is room to play. Just dont go past .50 for the squish.
    A machine shop in the states would charge around 60. dollars to do this.

    The wear ring can be worn and still look good. The more space you have between the prop and the wear ring the less effecient the pump is. I personaly have switched to the plastic wear rings because they are easy to change and alot cheaper. When i put my new wear ring in the blades of the prop are actually touching the wall and the ring has to be cut in when i first crank up the motor insureing almost no space between there.

  6. #6

    ok..

    Prop+housing and cylinderhead come clear thanks!

    Two more guestion i have, everybody has freeflow aircleaners, but it is hard to understand that the air flow in carburetors will be bigger whit those because the original aircleaner element is only a peace of metal and there is such large holes in it

    even tought that original cleaner box is heavy.. and it looks better whit freeflow aircleaners. but you guys all know is it worth to put those aftermarket cleaners?? one point is sure, making adjusments in carburetors is much easier if that stock cleaner arent installed.

    sorry bad english sometimes

    Second, solas impeller or skat-trak? solas is more expensive

    have a good day

  7. #7

    rivayamaha

    now i got offer to buy rivayamaha cylinderheah whit changeaple burningspace, is that good? it was guite cheap and good condicion.

  8. #8
    Old Ski Insanity w/rpm500's Avatar
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    that head is a good thing ,not a bullit proof modification like a stock head milled ...
    the changeable dome(burning space) orings have been known to leak at times so
    keep a supply of orings handy...

    what cc are the domes they are supplying? other wise you will have to order domes to get yourself in the right compression ratio..

    the air box doesnt streighten the air flow out like an f/a (flame arrestor)does ..and as you say its easyer to work on...

    dont worry on your english, its fine .. i cant speak finn at all so your 1 up on me!!

  9. #9
    jdog800's Avatar
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    [quote=w/rpm500;951312]that head is a good thing ,not a bullit proof modification like a stock head milled ...
    the changeable dome(burning space) orings have been known to leak at times so
    keep a supply of orings handy...

    what cc are the domes they are supplying? other wise you will have to order domes to get yourself in the right compression ratio..

    +1 I would also go with modified stock over oring head but thats jmo.

    The stock air box does give good signal with stock motor but if you go with more compression and other modifications it just doesnt give enough air flow to make the engine happy. One word of warning. Having to large an air filter can also give you not enough signal to properly bring in enough fuel and cause a lean situation. I would recommend the short style air filters rather than the large cone k&n style filters. These are really only for carbs that have no carb signal problems.

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