Thread: help! frustrated gp1200r newbie!
08-13-2014, 06:49 PM #1
- Join Date
- Aug 2014
help! frustrated gp1200r newbie!
Howdy all, great forum here so I signed up!
I have a 2002 gp1200r with an issue, have been searching and reading these forums for days and haven't found the answer I need yet so I'm asking for help.
Here's the scoop: last ran correctly fall of last season. This ski has a center cylinder rich miss that I cannot get rid of and it is limiting the ski to 6000 rpm/45-47 mph. (would run 7000 rpm and 70 mph previously)
this ski has a riva d-plate, chip and flame arrestors-all else is stock in the engine bay)
since this showed up a month ago, I have done the following:
1) completely rebuilt carbs with the following mods: removed accel pump, 110 pilot, 120 main, dull grey 95 gm spring, 1.5 n/s 45 psi pop off, arm heights etc all correct. low speed @ 7/8 turn, hi speed @ 1 3/8 turn. drilled returns and #95 jet in mag return nipple. (all mods from this forum thank you!) I left the choke operational.
2) had 105 hours on it and compression was down to 100-105 psi on all three holes, skirt clearance was up to .007" so I have installed fresh pistons/rings etc with proper r.e.g. and clearance is now .004" .
3) reeds are in beautiful shape. I have adjusted the fuel screws leaner on the problem cylinder but it does not help the issue.
4) crank index is right on and pressure testing shows me a tight sealed engine.
5) center plug wire and cap has been replaced and I have swapped the coil to another cylinder to see if the problem moves and it does not (center plug still comes out wet and cylinder has a noticeable miss right above idle all the way to wot.)
6)have manually cycled exhaust valve motor(again with help from this forum!) and watched valves actuate while riding ski with seat off.
7) I can not see a spark issue with an inline tester while riding but its very tough to watch!
fuel valve and all tank pickup passages etc have been flushed/cleaned/looked at/blown through etc and I have checked to "flapper door" as well.
9) exhaust system has been completely dis assembled and checked for restrictions or blockages and all is clear.
the mag and pto cylinders are running great and piston wash/plug readings are beautiful. the center cylinder still misses , the plug comes out wet and noticeably colder than the other two.
what have I missed here guys? I'm out of ideas unless its deeper in the ignition...trigger maybe? do these engines trigger each cylinder independently?
any help or similar experience feedback is much appreciated and sorry for the long post!
08-13-2014, 07:37 PM #2
- Join Date
- Sep 2012
What about proper power valve adjustement? There is a procedure in the manual that tells u how to properly adjust. Just a thought and a lot of times overlooked. Good Luck
08-13-2014, 10:38 PM #3
- Join Date
- Aug 2006
I just had a similar problem and it ended up being a couple of pieces of corroded aluminum stuck under the needle and seat. It was limiting fuel flow so much that cyl wouldn't fire (miss) at any speed just above idle. Did not catch it when checking out the carbs the first time thru because I checked pop-off and it was ok and blew thru all jets ect. I went thru most everything you did, looking at CDI, coil, plug wires, ect. The corrosion was in the passage between the carb internal filter and the N/S. Made the plug look wet because there was not enough fuel to ignite. I was ready to pull my hair out.
08-14-2014, 09:40 AM #4
...btw what are you meaning in your number 2 item of piston skirt clearance exactly? Between which surfaces? (there could be another possibilty/problem to check but have to ask that question first...).
Otherwise were you able to solve the problem yet?
08-14-2014, 09:29 PM #5
- Join Date
- Aug 2014
Thanks for the helpful replies guys. I did run through the power valve adjustments. Piston skirt clearance is the difference between the cylinder bore size and the piston skirt diameter. I use that as my main indicator to determine when a top end has run its course and this engine had for sure-
As tough as it is to admit, I just finished figuring it out at the lake today and it turned out to be stupid simple...the jetting calibration was just to rich for the center cylinder to run and realistically was to rich for the other two cylinders also although they were burning it.
Apparently, our Northwest Washington air is not as dense as most other locations. I ended up almost turning the hi speed fuel screws almost the way in and turned the low speed screws in 3/8 of a turn also before it quit burbling and four stroking in the low/mid and finally gave me the last 1000 rpm it was missing up top. So after that I did some jetting and my final calibration ended up being: 117.5 main (stock) 107.5 pilot (accel pump disabled) low screws are now 7/8 open (3/4 open for center cylinder) and hi screws are 1 turn open. All else mentioned above remains the same and the ski is really running sweet now at 7100 rpm and 70 mph, smooth and responsive bottom to top. I burned 9 gallons through it this way and it hasn't missed a beat so I believe this is my setup!
Great forum, I'll be back with my next adventure.
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