Thread: gp1200r top speed of 56mph!
10-26-2014, 10:19 AM #1
gp1200r top speed of 56mph!
List of mods:
free flow tube
wfo ibody carbs jetted and no chokes
dual feed to carbs
fuel flapper removed
fresh top end 130psi across the board on mac gauge
riva cast heads
reeds are oem but new
trued and welded crank
riva top loader
r&d ride plate
gp1300 pump extension
solas 13/19 prop
wfo holeshot kit
dplate n chip
each head is routed to a separate pisser for cooling
1200r water box
riva extended nozzle
carbs drilled and restrictor on return line
advent cdi rev limit at 7500
maybe some odds and ends im forgetting
I rebuilt this ski from the ground up. Redid the hull inside and out and went through every inch of the engine. New crank rods and pistons. Compression on stock riva heads show a steady 130psi on all 3 jugs. No funny sounds and it held 10psi for like 10minutes. All seemed good to go.
put her in lake and went for maiden voyage. It took off realy nice. Pulled hard out of a standstill. Felt when pv kicked in and it startedbto pull harder. All was good till topend or lack there off. I looked at my phone gps and im showing a max of 56mph. With a max rpm on dreamo of 6500rpm, Whooooahhhh. Tried playing with advent, no ater what setting, the same, plus or minus one mph but rpm the same. Disconected pv motor and set it manualy. Pig out of the hole but picked up and took of after a bit, only got to 56 again...
pulled her out of water and checked rideplate, shoe, prop, intake. Shit maybe something had fallen off. No luck. All was there and bolted up tightly. I get no cavitation on takeoffs so thinking its all bolted up correctly.
Put her back in water. Same results, no way it goes past 56mph, no mater what I do.. wide open run for a minute and a plug chop later resulted in a nice brown residue on plugs. All 3. Compression at this point is still 130 across the board. I rchened her up a 1/4 turn. Went down 1mph and plugs got darker. ???? Help.
10-26-2014, 10:41 AM #2
Hey there s2bu...
Seems like something is seriously holding you back on the end here.
- you should be somewhere around 10mph more on top end.
the first and obvious things to check..
1/. the intake grate isn't pulling down under load.
2/. the pump shoe isn't pulling out the hull.
3/. the rideplate isn't hanging below the pumpshoe.
4/. check you haven't sucked something into the intake grate area.
1/. ensure the power valves are lifting fully in all three cylinders. (the amount of lash between the cylinders is ridiculous)
2/. if you have it swap out the advent for a stock ignition. (i had an advent that wouldn't work for shit)
3/. what jetting are you running.? (what is the 3/4 to wide open throttle response like.? I'll guess at flat as shit)
4/. you say all the heads dump overboard.? how is the pipe getting it's cooling water supply.?
My initial guess is either the advent or you are too high on your jetting.
10-26-2014, 01:37 PM #3
10-26-2014, 06:23 PM #4
Would seem fairly reasonable then to assume it's not a hull issue.
would be helpful knowing what jetting is in the carbs at the moment.?
- also are you running the full air box assembly.?
I'm still thinking the advent or the jetting..
- perhaps you could post an image of the advent with the dip switches in the image.
-( is it remotely possible you have set the rev limiter to 6500 and not 7500.??)
Last edited by quadzilla; 10-26-2014 at 06:39 PM.
10-26-2014, 07:10 PM #5
Naw.. advent is set to snap68. First dip switch to on all others off=7500rpm, bottom switch set to aftermarket coils (originaly set to oem), riva single and both sensors off.
as for the jetting, its set up to osidebills mod and has no hesitation in any throttle position. Wfo set up the carbs before sending them out to me. Air box was never re-installed. Accel pump deleted and manual primer installed. Tau ceti flame arrestors are on. No chokes and all holes filled and port matched.
I have no indication of running lean. Just no friggin top end. Lol, I'm living up to my avatar name. Hahahaha.
10-26-2014, 08:08 PM #6
hey again s2bu...
not sure how you're able to get a snap 68.? (do you mean 58?)
- it may be an idea to try flipping switch one back to OFF and ON with all the others that'll give you a 7400rpm limit. (to confirm it's operating ok)
- advent recommends ON with all the switches. then go for a few wide open passes on flat water, note your max rpm, then add 200-300 on the switch settings..
before you do any of that you NEED to get water back into the pipe or you will at best melt your freeflow and at worst stick some pistons, or melt the exhaust port edge of a piston or three.!
the jetworks mod/holeshot mod might be keeping the waterbox cooled (if it's flowing?)
- but won't be doing anything for the expansion pipe and stinger..
10-26-2014, 08:17 PM #7
Sorry meant snap 58. Big thumbs small keypad on phone
I will dump pto head to pisser and run 1 and 2 to pipe as yamaha had it.
I will also put oem cdi back in and compare between both.
10-26-2014, 08:34 PM #8
- I'm thinking you're on the ever popular 110 low's and 125 hi's with a 1.5 N/S combo..
probably the only thing that's saving your motor just now is the rich jetting..
- I always preferred 120 hi's on a mostly stock motor.
How many hours on this motor since the rebuild.?
10-26-2014, 08:38 PM #9
Should be about an hour or so on complete rebuild..
10-26-2014, 08:49 PM #10
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