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  1. #1

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    GP1300R struggling to spin 14/22 at 7150+

    My GP1300R motor struggles to turn DF 14/22 at 7150+ RPM with the following mods.
    My best speed is 75mph-gps at 7150 rpm but that is with 2 bars of fuel, superman, 80 deg temp, 300ft elev.
    Normal riding conditions are 95+ deg, 4-8 bars fuel, sit or standup riding and then my max rpm's are 6950.


    2007 GP1300R
    - oem head cut by (the late & great) Oside Bill, 136 psi, picture included.
    - VF3 reeds
    - Riva EFI controller. Settings 3,7,1,9
    - 4 deg Key
    - Power Plenum FA
    - Stock sound suppression
    - R&D Ride Plate @ 0.840
    - Metal trim tabs
    - R&D AquaVein intake grate

    - R&D D-Plate (opened up additional 0.1 inch)
    - Cowels and seat airflow mods
    - Siphon Tube and visibility spout removed & plugged
    - 3 new pistons and rings at 131 hours. Cyl #2 repaired.




    I checked compression (10 hours after rebuild) and results are:


    Date: 4/14/15 (elevation 1370 ft)
    Hours: 141.3
    1: 136 (squish 0.057)
    2: 145 (squish 0.052) (cyl #2 was repaired by Millennium at 131 hours)
    3: 136 (squish 0.05


    From reading this forum it seems the target compression is around 150 psi.
    Is my lowish compression the missing link to make more power?
    Minimum squish is 0.052 with two layers of OEM head gasket.

    I measured one layer of gasket at 0.010, can I change from 2 layers to 1 layer which should result in min squish of around 0.042.
    How much psi of compression increase should I see going to one layer and will this make any significant increase in power?
    I can only get 91 octane fuel (10% ethanol) in CA, what is my safe compression limit considering also having the 4 deg key?
    Should I get the oem head cut again for more compression?



    I appreciate any advice, Ceril




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  2. #2
    novice duudu's Avatar
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    everything looks great. Keep fiddling with the boat settings . (ride plate , trim tabs , shoe)
    Also , ported throttle bodies gave me a pretty good boost.
    R-d plate opened up ? People on the forum did that with big bores but not always . Might rob you of some power.

  3. #3
    OzarkYamMonster's Avatar
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    Hello, yes ... 75 GPS is a great number for the listed mods you have. I noticed you have a milled head .... but only 135 to 145 compression? It would appear that you may be over propped. Lower pitch=higher RPM. However, 75 GPS is outstanding on a non ported engine.

  4. #4
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    My last run was 69mph on the GPS until my throttle cable broke, I should have no issue doing 70-71 with a little more plate adjustment. No engine mods but d-plate.

    I'm 130psi compression bone stock, to have a milled head at 136 that's low. You should be somewhere near the 150psi mark. I suspect your gauge is wrong, there's no way 136psi is going to run 75mph at 7150 with a 14/22.

    I would raise your plate up some more, put the OEM trim tabs back on with .030 spacer as the metal ones slow you down. Also is it a milled R&D or bone stock?

  5. #5

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    Duudu, According to WFO the early D-Plates for 1300 application were designed for 1200 and the later ones were designed for 1300. I had my 1200 spec dplate opened up 0.1 inches on the flat portion of cutout to match the 1300 dplate per WFO advice. A little less back pressure to go along with stock sound suppression which add a bit of back pressure vs blue tube.

    Ozark, Just to be clear the milled head picture is right after it was milled, no hours on it. Compression test history shows it has always read in the 132 to 136 range since it was milled. It was only after recent cyl #2 repair that cyl #2 read 145.
    Dont have an explaination for that other than fresh nikasil and hone. Both my compression gauges read the same by the way. I had my old DF impeller repitched to 13.5/21 and plan to test that in about 4 weeks to see if I can get my rpm up to where it needs to be in the 95+ temps where I ride, without loosing top end speed. I was hoping to get some answers on going from 2 layers to one on the head gasket and what safe compression limits are with 91 octane fuel.

  6. #6
    Prism's Avatar
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    I think he's referring to the metal tabs that came off the GP1200R skis. These are,the exact same as the plastic tabs only they don't flex at top speed when shimmed. The aftermarket extended tabs are slower because they're longer. Guys also cut them the stock length and shim them. When cut there is no speed loss over any stock tab. I had a long explanation about the squish and once again Tapatalk erased what I wrote because I bumped the screen. Stupid application. Yes yes yes get the squish to no more than .040 and no tighter than .035 or so. Oside domes with .040 squish should be about 150psi. (with stock port height which you have) Detonation resistance and power is highest at or below .040. An engine with 155 psi compression and tight squish will make more power and be prone to less detonation than one that's only at 140psi and squish at .058. I wrote as to why this is true before, but search Google for terms like, 2 stroke squish, combustion chamber boundary layer, engine quench, and squish for detonation resistance. Any questions pm me and I can fill you in. As for your ski... get the squish to .040 minimum, then, turn the 3rd pot to #4 on your fuel control, ride and turn down pot #3 until max rpm is reached, once there add a tiny bit of fuel back for safety (1/2 a number) get your plate height .950 or higher. Shim in small increments to find the sweet spot. If you bounce, add .030 washers under the tabs and step the sponsons. Do all this and then let us know what you run...Speed and rpm.
    Last edited by Prism; 07-11-2015 at 09:47 AM.

  7. #7
    Prism's Avatar
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    To answer more of your questions. On my 2003 GPR I run my squish at .037" and have 147psi compression. (Seems slightly low but my port height is higher than stock causing a slightly lower reading) I have used mid grade on the lakes during vacation and have had no issues. I've ridden hundreds of miles doing so. I ran with one layer removed for a while (2 seasons) on my ski. After determining everything was great I machined it .010 and returned to a stock 2005 head gasket. (Enhanced cooling passages on 05 and up head gasket) Never looked back since. FYI I opened my d-plate like you are and still use the stock ss. Do you have any pictures of the piston wash after your 10hr inspection?

  8. #8
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    Yes the plate must be .950 or greater... gotta grind that pump housing.

  9. #9

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    Hey Prism i sent you a PM, not sure if you got it.

    Regards, Ceril

  10. #10
    Prism's Avatar
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    Ok got it. Sorry was busy for a couple days. Return pm sent.
    Last edited by Prism; 04-20-2015 at 01:16 PM.

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