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  1. #1
    rhyne717xp's Avatar
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    Tuning aftermarket flame arrestors with accel pumps headaches.

    I have a project 96 xp thread already. I have gotten opinions from a local shop to disable the accel pumps on the 38/40i 99spx carbs i am attempting to run. I may try a few more attempts before I disconnect them. What do you guys think? Try to tune with accel pumps or disconnect them?

    Does anyone know if the pumps contribute to the total fuel delivery consistently or just when the throttle is hammered?

    I am thinking of trying a higher pop off than 21psi. Since the raw fuel gets injected when the throttle is hammered. Pop-off is most effective just off idle anyway. Opinions appreciated.

    Thanks.


  2. #2
    This is how I run a jetski shop in the desert nmpeter's Avatar
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    the local shop appears to be one to avoid for tuning advice. Clearly they don't grasp the concept of the need of the accelerator pump to overcome a metering issue

    To meet emission standards of the day, the engines ran lean, the accel pump was in place to prevent stalling when you suddenly transitioned between idle and full throttle.

    If you observe the operation of the pump, you see that the cam squeezes fuel out in relation to the speed the throttle is opened.

    With the aftermarket f/a you are likely running even leaner then expected.

    You need to do some plug reads to see where you are, but my first move would be opening the low speed screws 1/2 turn, leave the high speed screws shut and do some plug reads
    One running flat out to check the high speed mixture..then another after say 3 minutes at mid throttle cruise to see how the mid range is metering.

    Pop-off pressure settings keep the mixture steady during 1/4 to 3/4 throttle settings.

    Find the mikuni tuning manual..lots of really valuable info in there..

  3. #3
    rhyne717xp's Avatar
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    Quote Originally Posted by nmpeter View Post
    the local shop appears to be one to avoid for tuning advice. Clearly they don't grasp the concept of the need of the accelerator pump to overcome a metering issue

    To meet emission standards of the day, the engines ran lean, the accel pump was in place to prevent stalling when you suddenly transitioned between idle and full throttle.

    If you observe the operation of the pump, you see that the cam squeezes fuel out in relation to the speed the throttle is opened.

    With the aftermarket f/a you are likely running even leaner then expected.

    You need to do some plug reads to see where you are, but my first move would be opening the low speed screws 1/2 turn, leave the high speed screws shut and do some plug reads
    One running flat out to check the high speed mixture..then another after say 3 minutes at mid throttle cruise to see how the mid range is metering.

    Pop-off pressure settings keep the mixture steady during 1/4 to 3/4 throttle settings.

    Find the mikuni tuning manual..lots of really valuable info in there..
    Thanks, I have read the mikuni tuning manual a few times also the group k. I just need some more time, patience, and perseverance. I really have my heart set on using accelerator pumps. I have the OEM carbs too, I could jet to proks as well. I bought these 99spx carbs a few years ago to run on my 95 717xp.

    I have quite a bit of $ invested in those pumper carbs. They are in like new condition with a fresh rebuild kit.

    I am wanting to acheive the best take off and throttle response with what I have to work with.

  4. #4
    This is how I run a jetski shop in the desert nmpeter's Avatar
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    You have the needed materials..now invest the time and carful observation and you should be able to get it done.

    It _really_ helps to have a test tank for something like this, but you can do almost as well finding a secluded place where you can tie your jetski down to a trailer really well and run the crap out of it.

    it's hard to do a plug chop when you're standing in five feet or water.

    Group k stuff is really good for 951 tuners, I was impressed with their level of detail and obvious experience.

    I've heard glenn perry over at ppg was also a goto guy on 951 issues

    I never replacd the engine in the 951 I bought a few years aso..too pricey and I'm not a huge fan of the XP hull and seat setup being a bit of an older fart

  5. #5
    rhyne717xp's Avatar
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    Quote Originally Posted by nmpeter View Post
    You have the needed materials..now invest the time and carful observation and you should be able to get it done.

    It _really_ helps to have a test tank for something like this, but you can do almost as well finding a secluded place where you can tie your jetski down to a trailer really well and run the crap out of it.

    it's hard to do a plug chop when you're standing in five feet or water.

    Group k stuff is really good for 951 tuners, I was impressed with their level of detail and obvious experience.

    I've heard glenn perry over at ppg was also a goto guy on 951 issues

    I never replacd the engine in the 951 I bought a few years aso..too pricey and I'm not a huge fan of the XP hull and seat setup being a bit of an older fart
    Lol, GP is a great guy. I have talked to him personally on the phone. I chat with him on SD dot net here and there. I actually bought my proks, NS's from PPG. I try to buy from them when I need new parts. I found that Greenhulk gets better response in regards to two stroke skis than SD dot net. It seems it has evolved into a 4 tec site. Glen has valuable knowledge on ALL SEADOO'S.

    I could use a little help with all the rain I seem to get on my days off from work too. LOL!!!
    Last edited by rhyne717xp; 05-03-2013 at 08:06 AM.

  6. #6
    rhyne717xp's Avatar
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    Okay this the jetting im gonna try next time, the last settings were too rich. From what I figured from factory specs is that the accel pumps have a value of 7.5 going from 99spx specs. So I am hoping this will work. I plan on going up one size from 99spx stock settings and of coarse pop off @ 21psi with 2.0s
    Current jetting
    70 pilots
    142.5 Mag 145 pto
    highs 1 out
    lows 1.5 out
    using prok F/A's with outer wears.

    I have trailer tested on the hose, had great throttle response and came back down to idle fine.

    What do you all think? Lean or right on?

  7. #7
    This is how I run a jetski shop in the desert nmpeter's Avatar
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    what are the plugs saying?

    "trailer testing"..is for the honey boo-boo crowd. the only thing that will tell you is if your cold start setup is ok.

    you can't test an automatic transmission for shifting problems when the car is on blokc.

    you cannot possibly tune an engine without putting a load on it..and for a pwc..that means in water.

  8. #8
    rhyne717xp's Avatar
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    Quote Originally Posted by nmpeter View Post
    what are the plugs saying?

    "trailer testing"..is for the honey boo-boo crowd. the only thing that will tell you is if your cold start setup is ok.

    you can't test an automatic transmission for shifting problems when the car is on blokc.

    you cannot possibly tune an engine without putting a load on it..and for a pwc..that means in water.
    I can't wait to get back to the lake, I haven't had time, busy at work, weather hasn't cooperated, got a pregnant girlfriend etc.....ultrasound tomorrow . Hope we find out its a boy.

    Im gonna take a well deserved 3 day weekend this friday for some "me" time, get some tuning time.

    Plugs were black so i went down to 70 pilots from 72.5. I planned on starting rich but evidently WAY RICH. Better rich than sorry.

  9. #9
    This is how I run a jetski shop in the desert nmpeter's Avatar
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    while it's always been a point of debate, running too rich, in my view will lead to seizures, almost as easily as running too lean.

    think fuel/oil ratio on one side and oil/dilution on the other side

    it's like some guys insist on splitting tens at blackjack.

    don't diddle daddle to get it on the spot and perhaps throw a few oz's on injector oil into the gas tank

    good luck on the new baby

  10. #10
    rhyne717xp's Avatar
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    Quote Originally Posted by nmpeter View Post
    while it's always been a point of debate, running too rich, in my view will lead to seizures, almost as easily as running too lean.

    think fuel/oil ratio on one side and oil/dilution on the other side

    it's like some guys insist on splitting tens at blackjack.

    don't diddle daddle to get it on the spot and perhaps throw a few oz's on injector oil into the gas tank

    good luck on the new baby
    Thanks man, a couple of OZ's in the tank won't hurt a thang, I am actually impressed with how clean my 96xp burns, it smokes very little at start up then burns clean. My 717xp is a cheech and chonger for a bit longer. Lol
    I did ever think I would have kids, im 36 and never been married, found me a younger girl a year and a half ago, and here i am, LOL!!!

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