Help Please! Issues with a 98 GTX Limited. Will not take the gas.

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sledman1

sledman1

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Looking for some help on a 1998 GTX Limited (951). The engine starts and idles but sputters and backfires once you give it the gas and you get above about 1500 RPM’s. 125 psi compression both cylinders. I have swapped out the gray fuel lines. Cleaned the carb filters. Tried a second set of carbs with the same results. Cleaned the RAVEs and also tried a second set of RAVEs with no change in performance. Removed and inspected the Reeds. Tried running the engine with a fuel line going directly from the carbs to a gas can. Again no change in performance. Also tried spraying gas directly into the carbs while running the engine with ¼ throttle applied with little affect on the sputtering and backfire. I sprayed some carb cleaner at the PTO end of the motor while it was running to see if there was a bad crank seal on that end. No affect on the idle when I did that. The backfires are kind of a hollow sounding backfire. Not a real loud type. What is this type of backfire an indication of? Running lean? Timing? Any idea’s as to what else makes sense to check would be greatly appreciated. Thanks, Don
 
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Engine comp is a little low but it should run.
Try new plugs of the right type. I've seen new plugs that are bad out of the box. Make sure you gap them first. I don't have a manual for 98 but probably between .20 & .24 inches. This is the easiest and cheapest fix to start your diagnose.
A Bad Battery and fuses shouldn't make it run rough.
 
New plugs. Battery charged and in good shape. Compression 125 both sides. Did not check the fuses. Figure it would not run at all if a fuse was blown
 
did you clean your fuel selector switch? a gummed up/clogged/broken fuel selector switch could give you a delivery issue, as well as a fuel filter...did you replace the fuel filter? odds are that its the original and so clogged with crap...especially considering you live up near where i used to be, and the season is NOT LONG AT ALL, meaning, most ppl let those skis sit til next season with old/bad/dirty fuelin them, and then just try firing it up next season.
 
You have a 951 so a compression of 125 is fine. Spark plug gap is .021". Since you have already worked on the fuel system, I would look at the ignition. The first thing I would do is unscrew the spark plug caps, cut the wires back about 1/4" and screw the caps back on with new cable ties.

Lou

P.S. 96SPX makes a good point, I have never had much luck cleaning the fuel selector valve, I find it's best to just replace it, about $20.00.
 
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A clogged fuel selector switch is why I tried running the ski with a fuel line directly from the carbs to a gas can. I will check the plug gap but I would be supprised if that was the problem. I have tried a couple sets of plugs. I will also trim the plug wires and re-install the plug caps. The performance is really bad. If I had it in the water I would top out at 5 or 10 MPH. Thanks so much for your ideas.
 
yea, i'd do the fuel selector switch, and im not an expert, but i'm leaning toward running it with a line directly to a gas can kinda isn't the same as a closed/pressurized fuel system..so either way, you're gonna hafta get that fuel selector anyway..let me know if that helps/fixes your problem when your done....
 
I think you have an ignition problem, you have tried everything fuel related with known good compoants. Do you have a good ignition module to try? It does ack like it is falling on it's face at the transion point where the pilot switches over to the main but you have replace the carbs with known good carbs so that should rule them out. You have by-passed the fuel valve and even with miss gapped plugs it should rev up so all that is left is something ignition related. Another thing to check is the woodreff key on the flywheel, it could have sheared and cause the timing to be off. I also had a motorcycle that the pickup coil was too close to the flywheel and caused the plugs to fire at the wrong time and fire multiable times in one stroke. I hooked up a timing light to the plugwire and a "O" scope to the pickup coil and you could see the trash comming from the pickup coil and the timming light would constantly flash when you were just tring to start the engine. After finding this and looking really good at the flywheel and pickup coil you could see where they were touching.
 
Here is some additonal information on my issue. I swapped out the motor in my 98 GTX limited for a 99 motor. Found out the they changed th emagneto configuration between those years. The 98 has 2 trigger points on the mag and the 99 has 4. So I swapped out the magneto and installed the 98 magneto on the 99 engine. I lined up the hole in the fly wheel with one of the trigger points on the 98 magneto as decribed in both the 98 and 99 service manual. Now with the 98 magneto installed the ski will not run at all. I have spark and fuel. Timing must be so far off that it will not start. Chrisxp your right about the change in the coil setup but I would think since I have a 98 MPEM, Coil and Magneto that this would work. The magneto could be rotated and mounted in two other positions (6 bolt locations and two trigger points) changing the timing. Could I use a timing light to try and figure out how to mount the megneto? Or look at the position of the trigger coil to trigger points with the #1 cylinder at TDC? Getting cold here so I am about to bag this little project until the spring. Sure would love to get it set before I store it away. Thanks again for all your help.
Don
 
I am going to pull the magneto cover (again) and see if the position of the hole in the flywheel is different between the flywheel on the 98 and 99 motors. The manual has you use this hole in the flywheel to to properly align the trigger points on the magneto. This would screw up my timing if there is a difference in the position of this hole relative to the crankshaft keyway on the two flywheels (ring gear). If there is a difference then I will swap out the flywheel.
 
brock1 said:
Weak coil is a possibility i would test the spark strength coming out
Click to expand...

I had the motor running with the 99 magneto. Would idle but not take the gas at all. I think it was an issue with 4 pulses for every rotate being sent to the 1998 MPEM when it was designed for only 2 pulses per rotation. So I think my spark is good since it at least started before I swapped out the magneto's. Now I think the engine will not start because my timing is totally out of wack. As I stated in my earlier post that maybe the flywheels are different between the two motors.
 
98 GTX has one ignition coil
99 GTX has two ignition coils...Just a thought.

Crank position sensor/MPEM may not be able to read the difference between one coil and two coils.
 
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I know the timing for the 951 is 20 degrees BTDC at 3500 rpm's. Anyone know what the timing is at engine start up? I am sure it is much closer to TBC. Perhaps around 5 degrees BTDC??? Spent some time with a timing light. Looks like my timing while cranking the motor over is at about 65 degrees BTDC right now. If I were to rotate my magneto one hole location CCW this would put me at about 5 degrees BTDC while cranking the engine which I would think shifts up to around 20 degrees BTDC once the engines starts and I rev it up t 3500 rpm's. This must be done by the MPEM.
 
Swapped out the ring gear over the weekend and we are up and running. Yee haw! The ring gear was indexed differently between the 98 and 99 motors. To bad I got it running just in time to put it into storage for the winter. Just to summarize for anyone that might runs into this problem in the future. I swapped a 99 951 motor into a 98 GTX limited. To get the timing correct and to get the proper trigger signals going to the MPEM (98) I had to swap over the magneto and flywheel from the 98 motor to the 99. The 99 magneto has four trigger points compared to the 2 trigger points on the 98 magneto and the keyway that indexes the flywheel to the crankshaft is located in a different location relative to the alignment hole in the flywheel. Thanks for everyones help.
 
wow..crazy situation mang...good to hear your up and running...did you test it on the water at all, or just put it into storage? if so, what was your top speed?>
 
Just going to put it into storage. I think the top speed is around 60. Maybe some of the other members can chime in on what this particular model can do (1998 GTX limited).
 
Good to hear.
I knew when you said that you swapped motors that the complete ignition system along with the ring gear would need to be changed.
My 99 GTX will get 60/64 on the speedo, but the GPS is a more realistic 52/56mph.
 
My '98 GTX Ltd topped out at 52mph on the speedo this summer. It did have several issues though that are being fixed by Minnetonka4Me before it goes into storage, so next summer it may run a little better!:cheers:
 
ok, cuz mine topped out at 47.8 on the gps thats with a 717 on choppy water and BEFORE i replaced the broken motor mounts and properly aligned the motor..i took it out yesterday and it felt like it was DEFINITELY running faster, but we've got a crazy storm system going on here, so i didnt even try to take the gps out...had an IN-SANE ride yesterday though!
Almost felt like i had a "minnetonka4me avatar moment" for a second...then i realized i was not even a foot out of the air, lol
 
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