96 GTX Mid Range problem

[jjsinaz]

Hi Folks,

I had a thread going on this about a year ago. I got tired of trying to fix it because it was seeming that I was spending more time working on the ski than I was riding it. So I have just been living with the problem. I'm now ready to start fiddling with it again, hence restarting the thread.

The ski runs good at anything above 3/4 throttle and anything below about 1/2 throttle. Problem occurs between 3500 and 5000 RPM. Just seems like it's only running on one cylinder in that range.

Been through the carbs several times. Tried another set of carbs, Have played around with the adjustment on the RAVEs and rebuilt the water box regulator valve.

None of this seems to make any difference in the severity of the problem or when it occurs.

Engine was rebuilt by full bore last year and the problem has been there since having the new engine. Engine has good compression and runs well on the low and top ends.

Could rotary valve timing that is slightly off cause something like this?

Last year someone suggested that carb sync might be the culprit. I need to look at that and try syncing using MDs "sound" method. Could this be causing the problem?

I'd like to figure this out because I run it at 3/4 to full throttle most of the time because if you want to slow down to a cruising speed, it just falls on its face. (Really tears through fuel and oil too)

 

[jjsinaz]

Thanks but I know It's not the battery or connections. I've already been through all that. It's not hard to start either. Plugs look fine. After reading some other posts I can agree with you that its probably not the RV timing either. I think I'm going to start playing with the high speed jet. In reading Bill O's carburetor adjustments sticky, this seems to be a high speed circuit issue (1/2 to 3/4 throttle) I know some of the experts on here say that is it has stock jets and everything is adjusted right it should run right, but it doesn't and I am at a loss as to why.

 

[etemplet]

I worked through this on two GTXs last year. I pulled the carbs on both of them 5 times. It was an interesting journey. It's not your high speed jet either. I'd bet on the needles and pop-off, that affects the whole range of engine performance but to varying degrees. Something I've noticed is that even with Genuine Mikuni Needles and Seats , the new needles are lighter than the old ones. They seem to work OK and if you replace these along with installing the correct spring (order new ones) your pop-off will be around 38psi and it will seal around 30psi. This will help you transition greatly. Basically, I believe the needles are flooding the engine with fuel that it cannot burn.

Also put the carbs through the ringer again and make sure the three holes in the carb barrel are completely clear. A very good STRONG spray from all three. This will kill your transition if they are not completely open.

I'm currently fighting issues with a 1996 XP. It's all in the details. If you do some searches on my posts you'll see the issues I have with skis and what I've done to solve them. It's not always conventional wisdom that solves problems. Good Luck !!

 

[JeremyD615]

Hmm, I would definitely go through and sync the carbs. POPPS is right in that it won’t shut an engine down, but if you have one carb that’s hitting the transition circuit before the other, it will definitely run rough in that throttle position... It’s a pretty simple thing to check, so I’d start there.

 

[jjsinaz]

Thanks guys,

I'll check the pop off again last time I checked it was 38 psi. Also, I am 100% sure that the transition holes in the card throat are clear. The engine is not shutting down it just runs very rough in the mid range I'm also going to take a closer look at the sync on the carbs. Has to be something simple I just haven't found yet. I probably won't work on it until next month whenever the weather cools off a little here, but I'll certainly post up if I figure it out.

 

[biggiescott]

Thanks but I know It's not the battery or connections. I've already been through all that. It's not hard to start either. Plugs look fine. After reading some other posts I can agree with you that its probably not the RV timing either. I think I'm going to start playing with the high speed jet. In reading Bill O's carburetor adjustments sticky, this seems to be a high speed circuit issue (1/2 to 3/4 throttle) I know some of the experts on here say that is it has stock jets and everything is adjusted right it should run right, but it doesn't and I am at a loss as to why.

A guy at work had a very similar issue on a different machine and he found a loose/worn spark plug boot. He wiggles the plug wire while it was stumbling and it went away

 

[etemplet]

A guy at work had a very similar issue on a different machine and he found a loose/worn spark plug boot. He wiggles the plug wire while it was stumbling and it went away

I had this issue as well. Definitely worth checking out. Zip ties are on those boots for a reason. Some people clip 1/4" off the plug wires but I'd make sure I have the extra length on the wires. Ask me why. LOL

 

[jjsinaz]

Been there, done that. Thank you both for the suggestion though. I don't want to seem un appreciative of your help.
If any of you had ever watched the TV program "House" about a narcissistic Doctor who was always tasked with figuruning out the most elusive medical ailments this is kind of the same; you keep making suggestions until that "oh $hit" moment whne you stumble upon what the aliment is

 

[POPPS]

If I was trying to race tune a carb, your symptom (mid range rich gurgle), could be a pop off that might be too low, or a main jet that is too large,( usually the main ), but yours is stock,and I assume you have the stock spec jet. Carbs out of sync is also a possibility, and you can correct that by using a wide rectangular mirror that is wide enough for you to see both throat chambers, and then adjust the throttle connection arm till the openings at idle are the same. It's also possible that the O ring on your seat is leaking. Also a long shot, ensure the main jet is fully threaded (seated) in.

 

[etemplet]

If I wanted my skis to run faster I'd drop down a jet size. Whenever I add fuel it goes slower. That said... I'd rather give up some speed to have an engine that lasts. I believe Seadoo wants these skis running a little fat on top and I'm not arguing.

 

[jjsinaz]

Brings up another question, If I were to drop down a size on the HS jet, could the HS adjustment screw then be used to fine tune it?

 

[etemplet]

Yes it will adjust your top end fuel. I was considering doing just that on my skis to get a little more top end. If you do this to solve your problem.... good luck.

I found this information at the Factory Pipe site very insightful and helpful to me in understanding how the carbs work. Give it a read if you have not found it already. Factory Pipe

 

[jjsinaz]

What I'm thinking is that if I were to go down a size on the main and it addressed the midrange problem but was too lean on the top then I could compensate for that with the HS screw. Everything I've read states that the Main jet controls 1/3 - 3/4 throttle opening and the high speed screw controls from 3/4 to WOT, so this would seem logical to me

 

[etemplet]

What altitude are you running the ski? You are headed along the same path I was last year. I'm at sea level and I noticed the skis made higher RPM in May than the hotter months. Since density altitude gets up to around 2,300 feet in the summer I knew I could get more RPMs out of it. I even purchased the jets but didn't do anything with them. Skis are kickin and as I mention a little fat on top is more safe and keeps the engine cooler. Let us know how you make out.

 

[mikidymac]

Not exactly, it’s cumulative so at WOT everything is adding fuel from the pilot jet to the mains to the screws.

The HS screw is basically a half jet size.

Just do a plug chop at WOT and that will tell you if you are rich or lean instead of guessing at jets.

 

[jjsinaz]

Thanks Miki. Understood that its all cumulative. Based on that if I drop a size on the main and it improves the mid range, then it is going to be leaner from 3/4 to WOT I would need to open the HS screws to compensate for that. This is just a very annoying problem the engine runs really good from 3/4 to WOT, but when you want to slow down to a nice cruising speed, thats when it falls into the rough range and makes you not want to stay in that range. I'd like it to be as smooth as it can be in the midrange but understand that it is somewhat normal for them to run a little rough in that range, but the way this thing is now its like you shut one of the cylinders off whenever you hit that range. This would also lead me to believe that the problem is with just one of the carbs

 

[jaspruden]

I dont mean to hijack this thread but I'm having the same issue with my 96. For me to get from the low speed (2500 rpm) jets to the high speed jets (at about 4500 rpm), I can: (1) pump the throttle a few times or (2) pull the choke. Gets on the high speed and runs great.

Just wondering what happens when you are in that stumbling stage and pull the choke?

 

[JeremyD615]

Jaspruden, you should start a new thread for your issue, as it’s a different problem than the OP’s. You’re lean, and need to go through your fuel system and rebuild the carbs. Start a thread and we can walk you through it.

 

[mikidymac]

IT could also be the RAVE valves as some of the 1996's need the slotted raves to get over the midrange hump.

 

[jjsinaz]

IT could also be the RAVE valves as some of the 1996's need the slotted raves to get over the midrange hump.

Maybe that's my problem. My RAVEs are not slotted.