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  1. #1

    951 RX transplant in my GSXL, Carb Issue?

    I have a 1998 GSXL. I pulled a donor motor from a 2001 carbed RX(complete motor and carbs). I kept the 1998 GSXL MPEM, rear electrical, throttle cable, and oil pump cable and everything else. I mounted motor, replaced all fuel lines, cleaned my fuel selector, cleaned my gas tank, put in fresh gas, cleaned carbs(including filter screens), new plugs, set the low speed screws at 1.5 turns, set idle at 3000 RPM and replaced pump diaphrams. The motor fires up great, idles fine, but when I pull the throttle the motor hesitates then bogs(the motor will rev up, you just have to keep pulling throttle). In the water I can barely get it to idle and then dies when you pull the throttle. Today, I pulled the carbs out again, just to see if some junk got back in the carbs, but did not find anything. Tomorrow, I am going to bypass the gas tank and use an external tank to see if my sending unit may have had clogged tubes?
    It seems to be a carb issue, but could it be something electrical. The RX had dual coils(I still have electrical box from RX). I don't use the TPS because I am using the GSXL throttle and MPEM. I have been reading many posts here and could not find an issue exactly like mine, any input would be appreciated?


  2. #2
    RumRunnerRon's Avatar
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    Quote Originally Posted by Darkside View Post
    I have a 1998 GSXL. I pulled a donor motor from a 2001 carbed RX(complete motor and carbs). I kept the 1998 GSXL MPEM, rear electrical, throttle cable, and oil pump cable and everything else. I mounted motor, replaced all fuel lines, cleaned my fuel selector, cleaned my gas tank, put in fresh gas, cleaned carbs(including filter screens), new plugs, set the low speed screws at 1.5 turns, set idle at 3000 RPM and replaced pump diaphrams. The motor fires up great, idles fine, but when I pull the throttle the motor hesitates then bogs(the motor will rev up, you just have to keep pulling throttle). In the water I can barely get it to idle and then dies when you pull the throttle. Today, I pulled the carbs out again, just to see if some junk got back in the carbs, but did not find anything. Tomorrow, I am going to bypass the gas tank and use an external tank to see if my sending unit may have had clogged tubes?
    It seems to be a carb issue, but could it be something electrical. The RX had dual coils(I still have electrical box from RX). I don't use the TPS because I am using the GSXL throttle and MPEM. I have been reading many posts here and could not find an issue exactly like mine, any input would be appreciated?

    Timing issue perhaps? The Mpem was from the old engine. You may have to have the timing adjusted.

  3. #3
    Work Harder, Millions on Wellfare Depend On Us! ultramaxracing05's Avatar
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    the 99+ had a TPS sensor on the throttle cable.That controlled the timing.
    I recommend just changing the mag cup on that engine to a 98 model.


    the 99-up wont work since you have a 98 mpem.
    unless you change out the mpem to a 99+ but that will involve more $$$

  4. #4
    flyin' the friendly skies airbornexp's Avatar
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    Quote Originally Posted by ultramaxracing05 View Post
    the 99+ had a TPS sensor on the throttle cable.That controlled the timing.
    I recommend just changing the mag cup on that engine to a 98 model.


    the 99-up wont work since you have a 98 mpem.
    unless you change out the mpem to a 99+ but that will involve more $$$
    +1 changing the mag cup is much cheaper

  5. #5
    KrunchovXPL-GTX-RX's Avatar
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    The Mag is the same but as these gentlemen have so accurately pointed out, the cup is different (in both the number of magnets and the timing in relation to the crank key).

    I am a bit surprised it ran at all.

    I know of one instance (though it was the opposite, a '98 cup in '99+ boat) where all it would do was backfire (it even blew the exhaust hose off the water box).

    Get the right cup on there and I think you will be fine.

    As to the fuel. In theory, the only place other than the carbs that you will see a blockage would perhaps be the fuel valve or maybe the screen at the bottom of the baffle. I suppose one that is bad enough may have blocked lines, but that is too nasty to even want to think about.

  6. #6
    I started GSXL today and it is back firing like an old Model-T. I have a perfect shape mag cup from the '98 motor, sounds like great advice. I will yank the motor again and give guys an update when I change the the mag cup. Thanks for the input!

  7. #7
    Work Harder, Millions on Wellfare Depend On Us! ultramaxracing05's Avatar
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    Quote Originally Posted by Darkside View Post
    I started GSXL today and it is back firing like an old Model-T. I have a perfect shape mag cup from the '98 motor, sounds like great advice. I will yank the motor again and give guys an update when I change the the mag cup. Thanks for the input!
    once your at it, check the reed valves, most likely they are broken, it was not wise from your part to run that engine like that, a backfire on a 2 stroke that has reed valves is just asking for trouble.

  8. #8
    KrunchovXPL-GTX-RX's Avatar
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    Quote Originally Posted by ultramaxracing05 View Post
    once your at it, check the reed valves, most likely they are broken, it was not wise from your part to run that engine like that, a backfire on a 2 stroke that has reed valves is just asking for trouble.
    DING!

  9. #9
    Ok, checked reed valves and they are like new. Replaced cup. Fired up, motor runs good, no back firing, but still have carb issue. I cleaned the carbs real well and replaced pump diaphrams, but still have a bog when I pull the throttle. I have 3 sets of carbs I could use. The carbs I am using now are from the 2001 RX(all stock), the set from my 98 GSXL(has a smaller accelerator pump?), or another set that I have from a 1999 XPL, which has a primer kit installed and accelerator pump removed. I know I need to completely rebuild one set and go from there? Please give me some advice?

  10. #10
    Work Harder, Millions on Wellfare Depend On Us! ultramaxracing05's Avatar
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    did you check the pop off on the carb? and did you also check the small check valves on the diagphram plate?

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