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  1. #1

    Question Just done a hi comp re-build, carb adjustment?

    Heya guys, just a quick question, iv just had my 99 gp1200 non pv. It got a light port, 3 new oversized pistons, and a shaved and re-domed head (stock head), also replaced the little round fuel diaphragms in the carbs as the old ones were all creased. just did my first tank. So it all run in now. Iv noticed that it's a bit hesitant up top and whent I floor it from a standstill.

    Basically what I'm wondering is.. Do people generally need to adjust the carb low or hi speed fuel mixtures once doing what iv had done? As I'm thinking it feels a tad lean possibly now that it myt have a bit more power than be for??? Carbs felt all good b4.

    Iv got a prop, grate and sponsons if that matters.

    I'm goin to do a comp test this week to see what it's bumped up to compared to b4.

    Any help would be good cheers!!

  2. #2
    Yamaha artisan Cutlass's Avatar
    Join Date
    Oct 2010
    Madison, WI, USA
    I'd say yes, it probably needs some adjustment. Is everything else stock? Stock flame arrestor, stock jets, needle/seat, pop-off pressures, chokes, etc??

  3. #3
    choke plates are out now as i just put a primer in...

    yep everything else uv listed is stock..

  4. #4
    cfgp927's Avatar
    Join Date
    Dec 2005
    Warsaw, Missouri
    When you did your top end rebuild, did you completely rebuild the carbs? Or did you just replace the check valves? When you had your cylinders ported you stated changing your fuel requirements. Do you have a manual for your GP1200? I would suggest, you go back and rebuild the carbs completely, probably no need to rejet but start with the low and high speed settings about a 1/2 turn richer than factory settings adjust accordingly after bringing the engine up to temp

  5. #5
    HEY CFGP927,

    everything on the motor its sef is new (crank, rods, seals, gaskets, bearings, pistons etc)

    i have only replaced all the check vales in the carbs, nothing else.

    they ran beautifull before the re-build (crank bearing siezed due to dodgy work that was done on it b4 i bought it) i had good top speed etc

    is it true that the creesed check valves will cause it to run lean? this weekend i am going to come out half a turn with the high and low screws and see if i can notice the differance..

    im trying to find a rear seat in blue for it too at the moment as my plastic has gone brittle and started cracking from the wave jumping.. but im in australia and postage from usa would be heeps id assume?

    thanks for ur help so far too..

  6. #6
    Adam's Avatar
    Join Date
    Aug 2005
    Have a look at Osidebill's carb mods in these pages and you will see what needs to be done to stop the fuel pump valves from creasing.

  7. #7
    Took it out this weeken just gone and it's running great!! I did a bit of reading and decided to try sum br7hs plugs, was a bit puzzled at one point tho, as my dash was just sitting on 99kph and not going any faster.. Till I was cruising with my Nate on his rxp and he said we were cruising at 109kph!!! Lol my dash said 92kph!! And that was cruising at approx 30% throttle. But I would not gain any speed if I gave it any more throttle tho.. Was a slight chop on the river and a bit of a head wind. Any ideas why I can do my top speed at 30% throttle and not go any faster? Iv got a Solas prop, worx scoop grate and my worx sponsons were down. I'm running a standard ride plate at the moment... Cheers guys!!

  8. #8
    Would a R&D PRO-SERIES RIDE PLATE help me out with a few extra kph? Or will it scrub speed?

  9. #9
    Yamaha artisan Cutlass's Avatar
    Join Date
    Oct 2010
    Madison, WI, USA
    What plate are you using now, the stock '99 plate? The [email protected] ProSeries plate is a good plate. It'll be longer then the the stock '99 plate and helps get the front of the GP out of the water (when shimmed properly) which will help your top speed.

  10. #10
    Yep, just standard 99 gp ride plate at the moment.. Ok so I myt get one next.. Either that or I was looking at the extended nozzles..

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