1994 GTX Still Bogging on the Lake

[SigEp368]

Been fighting this unit all summer, and I am about ready to throw in the towel and scrap it. At this point, the engine will start and run fine on the trailer (no hesitation, no bogging), but on the water it bogs badly at and above 1/3 throttle, in fact the RPM does not increase at all through out the rest of the throttle travel ( no matter how much I feather it). Here is a list of the activities I have completed thus far:

1. Rebuilt carbs with Mikuni Kits using the sticky (twice)
   1. passed pop-off and pressure hold tests
   2. Used settings from seadoosource
2. New o-ring in fuel/ water separator
   1. confirmed seal with a vacuum hold test
3. New Fuel selector
   1. double checked clamps on all connections up to carb
   2. removed return line and verified flow out of the carb (plugs out using starter)
4. Rectifier
   1. Voltage test climbed to 14.5-15 V at 5K(ish) (no tach but I rev'd it pretty hard on the trailer, at least more than I am normally comfortable with).
   2. Disconnected the rectifier, no change in performance during lake test
   3. Fuses are both good
5. Compression test
   1. Cold block, Open Throttle (using Autozone gauge)
      1. MAG - 150 psi
      2. PTO - 145 psi
6. Wear Ring
   1. Replaced last year, maybe 4 hrs on it
   2. No obvious signs of wear
7. New Plugs
   1. Look a little wet, but I am running double oil, so it might be that.
   2. No fluid or oil sprayed out of cylinders with plugs out.
8. Lake Test
   1. At WOT, the motor dies if the choke is operated
   2. I tried spraying fuel/oil mix directly into flame arrestor (at WOT), with no change or improvement
   3. Adjusted Low/ High Speed with no improvement to response

The compression test seemed a bit odd, it took 4-5 secs to build to full pressure with many small jumps between strokes (see video below); however, it has the same pressure ramp up profile and final pressures as my 1995 GTX (657x), which ran perfect today. There are a few other odd things I have noticed, but I am not sure how these could be related:

• Gas gauge stop working, could this indicate an electrical problem?
• When greasing the fly wheel, I did not see the boot bulge after what should have been enough grease, could crankshaft seal be bad?

I am grasping at straws, and would appreciate any help or suggestions before I give up on it.

Please and Thank you.

 

[j.harris]

Shot in the dark here, have you looked into the rotary intake valve clearance? It's the only thing I haven't seen you mention on your list.

 

[PorknBeans]

I had a very similar issue on my '96 GSX after I rebuilt the motor/carbs and replaced some items that needed some attention. But when I put the ski into the water to adjust the carb's Low Speed fuel circuit. I could not get the engine to rev at all. It didn't matter how much I adjusted the Low Speed screws, in or out, under load on the trailer. The engine would not rev. No matter how much I feathered the throttle. It would just bog. During troubleshooting, I discovered the fuse in the rear electrical box had carbon build up on the fuse's legs and that created a high resistance from the battery through the fuse to the MPEM. I tossed the bad fuse(which visually looked a hot mess! Never seen that happen in my skis before!) and installed a new fuse and...BRAAAPP! The engine came alive and the throttle response was as it should be with more incremental low speed screw adjustments. So I guess in short...check the fuses again. Pull them out and do a continuity test on them or replace them with new ones and test those as well. Check the fuse seats(where they plug into) and test the cable from both sides of the fuse holder to be certain the cables are good. These tests will ensure that the proper amount of current is getting to the MPEM to power the DC-CDI and the MPEM for proper voltage to the spark plugs. As well as the other systems in the ski.

 

[j.harris]

I just realized the 94 gtx has 2 carbs. Check that both throttle plates open and close at the same time, something about them being out of sync causes all kinds of problems.

Also that's a crazy diag up there! Who would have thought a bad fuse.