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  1. #1

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    2000 gpr1200 big bore questions.

    hi all. i have some questions i hope someone that has done this can answer for me. i have a 2000 GPR1200 that i bought blown up. i have put in a new crank, new 1300 topend from lowell horning, 150PSI head, and new stock reads with a spacer. i have the D plate installed. i will put on aftermarket flame arrestors. i need to know what pitch impeller to run and what jetting to run. i will take the choke plates out and take off the accelerator pump. any input will help, thanx! oh ya....im around 500 ft above sea level.


  2. #2
    butterbean_29512's Avatar
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    See the sticky on gpr carb upgrade/accel pump removal in the yamaha how to section. Did mine, runs well, I'm in the middle of tuning it in.

  3. #3
    Quote Originally Posted by tacoma69 View Post
    hi all. i have some questions i hope someone that has done this can answer for me. i have a 2000 GPR1200 that i bought blown up. i have put in a new crank, new 1300 topend from lowell horning, 150PSI head, and new stock reads with a spacer. i have the D plate installed. i will put on aftermarket flame arrestors. i need to know what pitch impeller to run and what jetting to run. i will take the choke plates out and take off the accelerator pump. any input will help, thanx! oh ya....im around 500 ft above sea level.
    Did you ask Lowell about jetting specs? You may need to start a new topic specifically looking for jetting specs. Are the cylinders ported?

  4. #4

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    all lowell said was jet rich and work my way down...... he said the cylinders are ported. the exhaust ports are polished. after lots of reading i think a 14/25 impeller is a good starting point. for jetting.....
    Pilot 120
    Main 130
    N/S 2.0
    95 spring
    any thoughts?


  5. #5
    Quote Originally Posted by tacoma69 View Post
    all lowell said was jet rich and work my way down...... he said the cylinders are ported. the exhaust ports are polished. after lots of reading i think a 14/25 impeller is a good starting point. for jetting.....
    Pilot 120
    Main 130
    N/S 2.0
    95 spring
    any thoughts?


    I'll repeat the same good advice. Start a new thread specific to the jetting ofa 1200 with ported 1300 jugs. You'll need those inputs if you want to start close to final adjustments.

    I'm sure you realize the headache of getting to the carbs on the 1200...which frankly I think is why many guys go to the free flow.

  6. #6

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    talked again with lowell. this is what he said, in case any one is doing the same. OEM carbs: N&S =’s 2, Spring =’s 80, Pilot Jet 115, Main Jet 135. Low speed 1 turn, High speed 1.5 turns. Accelerator pump & chokes removed. Drilled returns w/ one jet (95) to restrict return flow. he agreed with the 14/25 impeller. thanx for the comments!

  7. #7
    Prism's Avatar
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    When you get it all together and start tuning, make sure you have an aftermarket pulse tach to record max rpms. They are accurate to a 10rpm window. I use a PET tach now, I have used a Tiny Tach but you need to hold the peak rpm for almost 2 full seconds for it to update and R&D lists a TTO tach for use with a GPR although I've never used one. Also get an accurate GPS thats mounted for speed readings. You may have to tweak HS settings between summer heat and fall coolness. Make sure you can pull that prop to 7100 rpm in the heat when done.

  8. #8

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    ok, just waiting for all my parts to come in. thanx!

  9. #9
    Are the cylinders ported? 14/20-14/23 max. 14/25 too much

  10. #10

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    cylinders are ported, head machined to 43cc. (should be around 150psi). the impeller is ordered, so if its to much i will have to get it repitched. someone else with the same setup but no ported cylinder was running the same impeller at just over 7000rpm. i thought sense mine was ported i could do it.....i mite be wrong! lol....

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