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  1. #1

    Join Date
    Sep 2010
    Lake Travis, TX

    2000 GP1200R Conversion to 1300

    I thought I would start a build thread to document my experience rebuilding/converting my GP1200. This all started 2 years ago when one of the washers bracketing the piston pin bearing got loose and wedged itself between the piston and cylinder. Fortunately the head had minimal damage and cleaned up with just a few pits leftover after machining. After some research and a last minute call to Rich at WFO, I elected to build a 1300.

    I sent my crankshaft to Competitive Crankshafts (recommended by WFO) and had it rebuilt, trued and welded. It came back looking great!

    I elected to go with Pro-X pistons for a 2003 GP1300 as they seemed to have a good reputation. I received the pistons and life overtook the project and things stalled out awhile. I happened to read a post about Pro-X pistons coming with the wrong rings for the type of ring locator installed in the pistons and sure enough, I had the wrong rings. Despite having the pistons for nearly a year, Atlantic Jet Sports and Pro-X took care of the problem and replaced the pistons and rings with a new set. Kudos to Jim at Atlantic Jet Sports for great customer care.

    I sent my pistons and cylinders to Millenium Technologies for boring, plating and finish honing to match the pistons. Soon after Millenium received my shipment, I got a message from them that they had damaged one of the pistons trying to remove it from my packaging. I was so paranoid about potential damage during shipping, I had wrapped everything in trash bags and then used spray foam to protect everything. Bad idea, apparently... One of the pistons had a shallow razor cut across the dome. Millenium reassured me that the piston would work fine and the cut would not cause a failure. Hopefully they are right... One of the cylinders required welding (I couldn't tell which one when I got them back!) and they also had to redo one of the cylinders so it took an extra couple of days.

    I sent my cylinder head to Group K for machining to match the new 84mm diameter of my pistons. I called several other shops and they were the only place that knew what was needed and could do the work. Group K also confirmed that I would need a larger diameter head gasket to match the new pistons, so I ordered a 2005 head gasket that has the better cooling for the #3 cylinder.

    I rebuilt the carbs, drilled out the return restrictor, removed the accelerator pump, capped the accelerator pump inlets, removed the tamper caps and rejetted the carbs. I epoxied the air channels in the manifold and installed V-Force 3 reeds from WFO. I left the choke plates and shafts in place as they were too much hassle to remove.

    From my (incomplete) research, I decided I could drive a 14/20 Dynafly prop. I rebuilt my pump housing and installed the impeller only to find the bearing hub was much smaller than the impeller outlet. This is when I discovered the difference between my housing and the HO pump housing. The HO pump has a larger diameter center section than the earlier pumps. I bought a new HO pump housing from WSM and this also necessitated buying a new pump cone, as well.

    I made aluminum plates to cover the exhaust outlet and the intake manifold and used a rubber gasket to seal the intake plate. I pressure tested the engine at 10psi and it lost less than 1/2psi after 30 minutes. Woohoo, I passed the pressure test! I sealed the cases and crank seals with 1211, put the base gaskets on dry and coated the head and exhaust gaskets with a thin film of grease. On the intake side, I used the 3-piece paper gaskets that came with the VF3 reeds and put Permatex High Tack gasket sealer on one side of each set of paper gaskets to hold them in place and to make sure none of the gaskets overlapped and created a potential leak. On the other side I put a thin film of grease. I guess it worked! I removed the plates, and installed the carb rack but stripped one of the 6mm threads that holds the intake manifold to the case. My bad. I forgot to use longer bolts to make up for the extra width of the VF3 reed kit. So the carbs came off and a Heli-coil went in, this time I used the correct hardware...

    With the engine assembled from carbs to exhaust manifold, I used a cherry picker and lowered the engine back into the ski. What a difference rotating the engine, carbs down, makes for simplifying this task. I bolted the cherry picker to the outer-most bolts of the exhaust collector flange, and this had just the right amount of rotation so that everything cleared the hull without even touching the side rails of the opening!

    While connecting the power valves, I discovered I had the shaft 180 degrees out of phase, so I had to remove all the cover plates, disconnect the lever arms and rotate the shaft 180 and button everything up. As I was torqueing one of the cover plate bolts, the threads stripped. F me... This one will get a Heli-coil some time after I get this boat running, or when it leaks oil, whichever comes first.

    More to come...
    Last edited by TwoGP12s; 07-08-2019 at 10:08 AM.

  2. #2

    Join Date
    Sep 2010
    Lake Travis, TX
    List of Modifications

    Drilled return restrictors and added 100 jet in return line (changed restrictor jet to 90)
    Extended both fuel pickups to bottom of tank and removed flapper
    Filled intake manifold channels for better carb signal
    V-Force 3 reeds
    Rebuilt and Rejetted carbs, removed tamper caps and accelerator pump
    Removed Fuel Selector and added a 2nd fuel filter
    Added Fuel Pressure Gauge
    Added primer to all 3 carbs using oil injector port. Added a 3-port fuel filter in the return line as a small reservoir for primer fuel
    Removed stock airbox and added Pro K flame arrestors
    Capped the original ports for the accelerator pump fuel
    Replaced all the fuel lines with Low-Permeation Fuel lines. Also used Low-Permeation Tygon primer lines. - MAJOR FAIL !!


    135 Main Jet
    115 Pilot Jet
    1.5 Needle
    80g Spring
    Popoff adjusted to 38psi
    2psi at idle, 7psi at WOT - #90 restrictor jet in return line

    Pro-X pistons - 84mm
    Millenium overbore, replate and hone to finished size

    Group K machined for 84mm (Compression 127-129)
    2005 1300R Head gasket with improved cooling for #3

    D Plate and resistor
    Riva Free Flow - removes resonator
    Manifold gasket modified to increase cooling flow to #3 (lower holes same as #2)
    2003 GP1300 new-style power valves - these have the larger diameter bevel to match the bore size for a 1300
    Installed '05-'08 Ring Joint exhaust pipe

    Outlet from cylinder head between #2 and #3 dumped overboard and corresponding exhaust water inlet plugged
    2005 Head gasket and modified exhaust gasket (as above)

    Jet Pump
    14/20 Dynafly Impeller
    HO Pump Stator/Bearing housing and matching cone
    Blueprinted HO Pump Stator
    Grease/ATF mix for lube
    Rooster tail port plugged
    Suction pipe trimmed shorter
    Pump Seal kit installed and pump shoe sealed with 4200
    85mm Exit Nozzle installed (original is 87mm)

    Replaced the Ride plate and intake grate threaded hull inserts with the single piece versions
    Added an electric bilge pump with a lighted on/off switch
    Increased the airflow capacity of the side covers
    Installed R&D Speed Plate

    4 Degree advance key
    Removed oil injection pump, installed block-off plate
    WaveEater Power valve connectors
    CanDoo GPS speed sensor
    Pet-2100dx Tachometer - Blue wire in attached image
    New traction mats
    New seat cover
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    Last edited by TwoGP12s; 09-14-2019 at 07:50 PM.

  3. +1 by:

  4. #3

    Join Date
    Sep 2010
    Lake Travis, TX

    Got it started today! YESS!! It idled pretty smooth, too, all things considered. I only let it run for 10 seconds or so as it wasn't on the hose. Before starting, I had to fix a leaking primer hose and there are a few other issues with the primer circuit that needs attention, like why fuel won't flow to the back 2 cylinders...


    I also noticed last night that the Power Valve servo wasn't cycling, but it will return to closed, if I manually move it open. More trouble shooting to follow, but this may explain some of the power loss I noticed before I found the bad cylinder... At least it is adjusted properly - the hole in the pulley aligns with the hole in the power valve housing on the cylinder. Yep, definitely bad. I ordered a replacement off eBay for a decent price and the seller claims it works perfect, so we'll see.

    Low Permeation primer lines suck! I worked on the primer lines and discovered the problem. The tubing I purchased has an inner liner that is resistant to everything known to man so I thought it would be a good choice. It wasn't specifically marketed as low permeation, however, but it was highly resistant to chemicals according to McMaster-Carr. The problem is that the liner is not adhered well to the outer jacket. With the small primer fittings, it is very easy to misalign the tubing, especially when you are pushing it on by feel. Well, I managed to fold over the liner and the fuel dissected the complete length of the liner from the jacket and nearlyy occluded all flow! When I pulled the tubing off of the first tee, the whole liner came out stuck to the tee while the jacket pulled off of the tee. So, I had to replumb the whole primer system and that meant the stinger had to come off again for the umpteenth time...


    Got the ski in the water today and rode for close to an hour and burned up ~6gal of premix. I zip tied the power valves open for now. I tried to keep it below 5000rpm for that ride, but it is hard; it really grabs the revs!! A little drama with the eBay seller , but we worked it out and I should be good to go by next weekend for the replacement power valve servo!

    With the cooling mods, I'm not noticing water out the starboard pisser. Good flow from the added outlet and the port-side pisser. I matched the through hull size to the water outlet from the head, but I'm wondering if the 5/8" through hull is too big and that's why I'm not seeing any water out the starboard side...(It turned out I had the stinger rubber coupler slightly rotated so that the water outlet was not at the bottom of the coupler. After rotating the coupler to reposition the outlet, I am now seeing water out both pissers).

    The fuel pressure was a little low, barely off the stop at idle and less than 5psi at 5000rpm, so I will need to go down a size or two from the 100 jet in the return line.

    I checked compression after my ride and they were all between 125-128 (cold compression was 127-130) with all the plugs out, running off the battery only. I guess I'll do a solder test to check my squish band and see if I can remove the center layer of the head gasket (Nope, my gasket only had 2 layer from the start...DOH! ).

    It's good to be back on the water!!


    I replaced the power valve servo with a model from a 2000 XL 1200. The cables and bracket are different, so I had to use my old cables, but everything matched up just fine. The power delivery is now more linear, not as abrupt as it was with the power valves locked open. WooHoo!

    I also changed the return jet from a 100 down to a 90. This definitely helped the off-idle/low rpm fuel pressure and I now see 2psi at 2500-3000rpm. It was too rough today to do a sustained run at WOT and look at the fuel pressure gauge but I'm guessing it is in the 6-7psi range. It looks like the 90 return jet may be a keeper for my setup. I'll keep an eye on this as I start to tune the carbs and see if I can lean out the idle and maybe a bit on the hi speed circuit, as well.

    My last 2 attempts at getting decent borescope pictures were hindered by the bright daylight, which completely washed out my laptop screen. I'll try again after dusk and see if I can get a decent image of my piston wash. I have a 10-15 minute ride through the no wake zone to get back to the dock and this may complicate things a bit...

    I had planned to install new traction mats today, but the instructions say to let the mats sit for half a day to let the adhesive fully cure after installation. This could be a challenge! It's also time to replace the seat cover again. My old cover is disintegrating now that I'm riding regularly again. Oh darn !


    I installed the CanDoo GPS speed sensor and calibrated the sensor to my gauges. I tie wrapped the unit to the fuel filler hose for now. I may change its location later. No more Dream-O-Meter!

    Borescoped the engine after dusk. It was much easier to see the image on my laptop. The piston tops are slick with oil, no doubt caused by the 10-15min slog through the No-Wake zone and the rich mixtures. I've switched over to synthetic oil and dropped the ratio down to 40:1, but there is still no discernible piston wash. I still haven't leaned the mixture yet.


    Got the new traction mats installed. WooHooo!! It looks better already


    Installed the PET 2100dx Tachometer. Adjusted the carburetors - my T Rex arms can not reach the forward carb idle mixture screw, even if I remove the battery box and electric box. So, out came the stinger yet again. I adjusted the idle screws to 1 turn out (from 1-1/2) and I set the mains to 1-1/4 out (from 1-3/4 out) except I adjusted #3 (PTO) to 1-1/2 out. The engine started right up and after a minute of idling in the no-wake zone I goosed the throttle and the engine promptly died. Uh-oh, did I lean the idle mixture too far?!?

    The engine started right up again and I motored out of the no wake zone. This time I slowly added power and there was no hesitation and it pulled hard all the way up to WOT. Cool! I tried a few throttle snaps to WOT from idle and the engine revved with abandon! Phew, it sounds like the idle screws are about where they need to be. Sustained runs at WOT showed no signs of heat saturation and no loss of rpm, so all looks good for now.

    I think I'm hitting the rev limiter with the Dynafly 14/20 impeller. The engine revs hard right up to 7200rpm and holds right there. It feels like the engine could easily rev to 7500 or more. I'll seek out some expert advice on whether I should try a higher pitch impeller or stick with what I've got and enjoy the acceleration.


    I thought I was hitting the rev limiter, but I have been told the RPM limit is 7400-7500. On smooth water it's steady at 7170rpm and 67mph (GPS). I went for a 80 mile ride today with a few stretches of perfect water. I had a sustained run of nearly 15min @ WOT and a steady 67mph with 1/2-3/4 tank of 40:1 premix gas. I'm pretty happy with the ski right now. Once I get a decent picture of my piston wash I'll post the pics. About the only mod I'm contemplating now is taking the middle layer out of the head gasket to bump the compression a touch (turns out it was already a 2-Layer head gasket).


    Installed an 85mm jet pump exit nozzle today. I picked up 1 mph and my rpm's dropped ~20-30rpm. Next up is the '05-'08 ring joint pipe.


    Installed the '05-'08 ring joint pipe, but there was no smooth water where I could test the results. I painted it black to sorta match my stock exhaust to maintain the pseudo stock appearance. Next I'll check the squish clearance and remove the inner head gasket layer(my bad, it was a 2-layer gasket all along). I'll post piston wash pics and compression numbers at that time.


    I was having problems testing the exhaust change above. My PET 2100DX tachometer was showing erratic readings above 6800RPM. I got it sorted out today but there was no smooth water for testing. However, it looks like this change brought the RPM back up to a steady 7200 RPM. Unfortunately, this did not translate into a measurable speed gain with the CanDoo GPS mod. Subjectively, the ski definitely accelerates more quickly to 68, but it can't quite make it to 69mph. I could probably get to 70 with a ride plate change, but that is more money than I want to spend, and I don't want to give up any rough water handling/performance ( I.HAVE.A.NEED.FOR.SPEED. I couldn't resist and ended up buying a R&D Speed Plate).

    I pulled the head last night and checked piston wash and replaced the head gasket. When I took the ski out the next day, it ran terrible. WTF?!? I pulled the plugs and they looked a bit oily but otherwise unremarkable. Compression was close to baseline. I put in new plugs and torqued them to 15 ft-lbs and went riding again. It was a different ski right from startup and was back to its normal agro behavior. I'm happy again.

    Piston wash after 15hrs looks a touch lean, but there is a clearly discernible 1/2" semicircle adjacent to the transfer ports that are getting scoured by the fresh air-fuel inflow. I'll post the pics here but will seek feedback in a piston wash thread. I'll probably open/richen the hi-speed jets 1/4 turn before it cools off in the fall.

    I rode the length of lake Travis and back, roughly 120 miles, and I averaged 50-55mph for most of the trip. It was a beautiful day on the water!


    Rode about 35 miles (one way) to find smooth water for some speed runs. It was still a little breezy, but 69mph was no problem. I finally got far enough up the Pedernales river where it was smooth and sheltered from the wind and 70mph was mine. I was seeing right around 7230rpm with a slight tendency to porpoise. Not sure if this was the water conditions or the ski, but the porpoising was bad enough that I think it made 70 difficult to achieve until I was on just the right water conditions.


    I think I Hydrolocked the ski today. I was out riding, having fun, taking a lot of water over the bow and handlebars and the ski got real rough, lost power and eventually died. I got it restarted and limped back home. Later that evening I pulled the plugs and checked the compression: 130-30-130. The borescope didn't show any anomalies, but I didn't move each piston to the bottom of it's bore before I took a look. I'm going to pull the engine and tear it down to troubleshoot. I don't want to do this down on the dock with the engine in the ski. I'm pretty certain I bent a rod...

    I pulled the motor and found a bad piston. Thankfully, the rod looks fine. I sent the cylinder off to Millenium for repair and replate with a finish hone to match a new piston.

    The engine is finally back together after dealing with a few issues. Once again I got the wrong rings with my Pro-X pistons...unbelievable. Pro-X took care of the problem, I just had to wait for their next production run. Millenium also sent me a Pro-X piston with the wrong ring set, but they also took care of the problem promptly. I did have a problem with the power valve not moving freely through its full range on the newly plated cylinder, but a little bit of quality time with a file or two remedied the problem. And, believe it or not, the piston I received from WSM had a ring problem - they only sent me 1 ring instead of the required two. They too, took care of the problem. What is it with me and piston rings...

    Anyway, I got the cylinders assembled, finally, and the head bolted on with a late model gasket. I modified the exhaust gasket to increase the #3 cooling and installed the header pipe. While putting the carbs on, I stripped the very last bolt and had to pull the rack off and place a heli-coil in the thread (and yes, I was using my Snap-On inch-pound torque wrench). Before I started engine assembly, I had disassembled all my carbs and found creased fuel pump check valves on the carb with the bad cylinder, so I replaced all of the check valves. Everything is back together now and I hope to install the engine tomorrow when I get home from work. WooHoo!!

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    Last edited by TwoGP12s; 03-28-2020 at 12:01 PM.

  5. +1 by:

  6. #4
    Hi. what are the final adjustments of the H and L ?

  7. #5

    Join Date
    Jul 2019
    Buffalo, NY
    Great writeup!!

    We just pulled the carb rack off and I was surprised to see no gaskets on the reed cages or retaining plate... only the carb rack. Am I missing something or should I used the high tack sealant?

  8. #6

    Join Date
    Jul 2019
    Buffalo, NY
    How's the ski been running? We have yet to pressure test the block and see what we really have going on.

    I am intrigued with the #3 cooling mod. I haven't heard of that yet.....
    please elaborate.

  9. #7
    Where do you live on lake Travis. Iím in Lago Vista mile marker 26 across from Briarcliff. A friend blew his 1200r motor a couple of weeks ago. Looking to reassemble as a 1300r. I have a 14 FZR on my dock.

  10. #8
    Adam's Avatar
    Join Date
    Aug 2005
    It’s running a bit lean still ! The pistons should be shiny around the outer edges ( No carbon) . This is because the piston crown is getting hot enough to burn the oil and carbonise the outer edges . Go richer on the main jet 137.5 .

  11. #9

    Join Date
    Jul 2019
    Buffalo, NY
    Any updates?
    I sent you a PM regarding the epoxied intake crossovers

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