Restoring a 94 GTX have an issue

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laptop4079

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Hello everyone, go easy on me it's my first post. I'm normally really good at sourcing my own information but I want some feedback on what my next step should be. I've always wanted a jet ski so I found a really cheap one and bought it and of course it didn't run. I've rebuilt the carbs and jet pump but I'm now having a problem with the low speed adjustment. From an idle if you give it throttle it bogs. I can get it going by blipping the throttle to raise the rpm and then I can take off. It seems no matter how far or what direction I turn the screws nothing drastic happens. All the fuel lines and both plugs have been changed and I've clipped the spark plug wires back. It has the 657 with the dual mikuni sbn carbs. I've also noticed fuel and oily froth being spit back out of the carbs. I've timed the rotary valve multiple times to make sure it's correct and when I had it apart I did notice some light to medium scoring on the rotary valve cover. I've spend a decent amount of money rebuilding this thing the correct way and I want to make sure I'm pointed in the right direction in replacing the rotary valve and cover.


Thanks!
 
There are known issues with aftermarket kits. Not sure if this is your issue but I would use the the right parts to keep from chasing my tail with carb related symptoms
 
Make absolutely certain the 3 holes in the middle of the carb barrel are clear. There is a 4th hole a little to the left but it is easier to see. You try to plug that one with your thumb when checking to verify the others. This is how I do check.

have the low speed jet removed from the carb and the low speed adjuster in place. use something to block the thorttle wide open so you can see in there. NEXT.... can of carb cleaner or some solvent to spray into the low speed jet hole. You'll need one of those red straw things on the end of the spray can. You should be able to see strong streams of liquid flowing into the barrel.

A bit long but hopefully helpful. If those holes are not flowing the carbs won't transition very well. Also... do not poke around those holes with anything. If you make them larger the carbs are junk. Good Luck
 
Make absolutely certain the 3 holes in the middle of the carb barrel are clear. There is a 4th hole a little to the left but it is easier to see. You try to plug that one with your thumb when checking to verify the others. This is how I do check.

have the low speed jet removed from the carb and the low speed adjuster in place. use something to block the thorttle wide open so you can see in there. NEXT.... can of carb cleaner or some solvent to spray into the low speed jet hole. You'll need one of those red straw things on the end of the spray can. You should be able to see strong streams of liquid flowing into the barrel.

A bit long but hopefully helpful. If those holes are not flowing the carbs won't transition very well. Also... do not poke around those holes with anything. If you make them larger the carbs are junk. Good Luck
Sorry for the late reply.When I first rebuilt the carbs I cleaned them for a few hours in an ultrasonic bath I rotated them every 30 ish minutes and blew air through them before during and after. I'll take them off again and see if I can see the holes in the side. Does anyone think it'll be worth it putting a new rotary valve and cover on since I have to take it apart again?
 
If you installed an aftermarket carb kit you best approach would be to install a NEW Genuine Mikuni kit with Needles and Seats and the proper spring. I've chased my tail previously with aftermarket kits and even tested those kits side by side. Now.... there is no way I would consider installing anything but Genuine Mikuni. That said, I'm not telling you what to do just relating my experiences and those of much more experienced Seadoo mechanics that I chose not to listen to at first. LOL Good Luck and enjoy the journey. :)
 
If you installed an aftermarket carb kit you best approach would be to install a NEW Genuine Mikuni kit with Needles and Seats and the proper spring. I've chased my tail previously with aftermarket kits and even tested those kits side by side. Now.... there is no way I would consider installing anything but Genuine Mikuni. That said, I'm not telling you what to do just relating my experiences and those of much more experienced Seadoo mechanics that I chose not to listen to at first. LOL Good Luck and enjoy the journey. :)
I think all of us that are out there trumpeting for using genuine OEM parts went through that same experience... It usually goes like this:

You have a problem that seems carb related, so you buy an inexpensive rebuild kit.

Then you start doing some research on how to do the job and find a handful of people screaming that you shouldn’t install anything aftermarket.

Since you’ve already got the parts in hand, you go ahead and rebuild it with what you’ve got, only to find it doesn’t work right.

Eventually you wind up here asking for help on a bog/surge/idle issue that you can’t get rid of no matter how you adjust the carb.

Ultimately you have to buy the OEM parts and do the whole job over again...

Just remember, those that are the ones pushing the hardest for Mikuni parts, have all gotten there by basically the same route, and they’ve made that mistake personally...
 
OK, I have no issues with going the OEM/Mikuni genuine parts route....however.....I've just rebuilt my '96 carbs (with SBT kits) and very meticulously checked that every piece and part was installed properly and correctly. The ski starts on the button push and idles perfectly (on the trailer and on the water).

On the trailer...the ski would throttle UP with absolutely NO HESITATION, rev hi/low, hold high RPM's...no issues whatsoever.....NOW here is the problem.....on the water...the ski will start right up but can't / won't throttle up...it is the damndest thing.....it'll idle just fine but she bogs right down on the throttle press. I'm scratching my head...WHY does it behave well on the trailer but not on the water....WHY would the carb rebuild kit NOT be at fault on the trailer but AT FAULT on the water...that doesn't make any sense.

BUT I am also chasing the dreaded 12V LOW problem (I know I have good battery voltage, new rectifier/regulator, new battery cables, new starter, new coil, new solenoid, clean connections, etc.....).....I also have the Wiring Diagram for the ski and I THINK I have it narrow downed the problem to:
1) bad stator (but how/ why would the ski otherwise behave properly otherwise if the stator were bad ???, obviously the induction pickup is getting signal to fire the spark plugs properly (the ski starts and runs, leading me to believe that the stator is fine),
2) bad rectifier/regulator (possible)....I have NOT checked the RED wire out of the rectifier for 12/14 V DC yet,
3) bad wire somewhere in the harness assembly(s) perhaps between the RED OUT of the rect back to the solenoid (I will test red wire for DC voltage out...if that checks out...then I'll jumper the red wire directly to the battery to watch for battery voltage above 12V dc when the ski is running....right now....the battery is NOT showing 14.4 +/- while the ski is running (so that confirms the battery is not being refreshed by the electrical system - skis don't re-charge batteries, they just put out DC voltage to the battery to keep it charged at 12.2 or better).....

The ski is on the water 3 hours away from me, so I only get to play with it on the weekends (when I'm not doing 100 other things)...which is never....haha.
 
I went back and looked over the thread, but maybe I missed it.... have you checked compression? Low compression would give you this same type issue. On the trailer there is no resistance for the motor to over come.
 
Compression is strong....tested both cylinders.

The ski ran hard and strong last season too....had the 12V LOW problem though (which made it finicky to start by the end of season - as the battery was struggling).....

New battery this season, etc......new fuel pickup, new gas lines, new oil lines....I've basically rebuilt this thing on the inside.....I think I'm close.....but no cigar YET! BUT I will prevail...either through sheer determination or abject stupidity (mo money, mo money)....I'm stubborn that way....
 
The way the ski runs on the trailer can be misleading since there is no load on the motor. How it runs while on the trailer is essentially useless as far as diagnostics go... Think about how much throttle it takes to hit the limiter while the ski is on the trailer. The carb is barely out of the idle circuit... Then when you put the ski in the water, you have the motor loaded up and are using all of the different circuits of the carb.
 
Yes, I comprehend that but I can't necessarily agree wholeheartedly...but how much different is it really hitting the throttle in the air (on the trailer) versus on the water......how would the ski KNOW the difference? Hitting the throttle loads the engine WAY above the idle circuit......sitting on the trailer or on the water.....in either case the drive shaft is spinning through air or water and water doesn't offer THAT MUCH resistance as the ski is designed to plow through water.
 
Yes, I comprehend that but I can't necessarily agree wholeheartedly...but how much different is it really hitting the throttle in the air (on the trailer) versus on the water......how would the ski KNOW the difference? Hitting the throttle loads the engine WAY above the idle circuit......sitting on the trailer or on the water.....in either case the drive shaft is spinning through air or water and water doesn't offer THAT MUCH resistance as the ski is designed to plow through water.
It's a huge difference in resistance. Leave the ski tied to the trailer and back it in the water. You won't hit the Rev limiter, but will quickly bang off the limiter with the ski out of water
 
You are wrong. THe ski will run perfectly on the trailer because there is absolutely zero load on the engine so with basically no fuel it will rev all the way to the electronic limiter. The engine is basically free spinning.

On the water you are at full load and it takes all the fuel and air the carb can process to get up to speed.

Let me be very clear... It IS the junk carb kits you bought from SBT.
 
I concur... I can completely understand the resistance to believing it’s the source of the problem also though. There are a lot of companies that are out there selling aftermarket kits, and you wouldn’t think it would make business sense to offer a product that doesn’t work. Unfortunately they just don’t, and people keep buying them only to have problems. A quick search of the forum will literally bring up dozens if not hundreds of instances where a fueling issue can be traced back to aftermarket carb parts...

As for how the ski “knows” it’s out of water, the motor has FAR less load on it turning the impeller in air vs the water. If it were a similar load, the ski would create just as much forward momentum pushing air through the pump as it does in the water... Since the load is so much less, the engine has very little resistance and can rev to the moon with very little fuel throughput. I know we don’t have manifold pressure sensors to control fueling on these old carburetors, but manifold pressure is what operates the carbs, and the load on the motor directly affects the amount of fuel pulled through them, so the ski does in fact “know” that it’s being run out of the water.
 
If you read the repair manual Idle is set to 3000prm on trailer, and the same setting drops the rpm to 1500 in the water. So there is more resistance in water than on the trailer...
 
Great info guys.....love the insight and education.

OK, so it sounds like a carb rebuild AGAIN with MIKUNI kits.

QUESTION though.....WHAT part(s) of the kits might be the issue? The gaskets, check valves, diaphragms etc...all were identical to the old and were all perfectly cut and I made 100% sure I matched the new to the old piece for piece and all the orientations at re-assembly were correct as well....so I'd find it hard to point at any of those items to be problematic.....hmmmm, I wonder if I just re-used the old needles and springs would it make a difference? (I used the new needles and springs from the kits, but kept all the old parts). I cleaned the snot out of everything as well, working methodically on the bench in good light.

NOTE: Visually, I could not "see" a difference between the old and new needles and springs BUT the ski did run strong last season on the old carbs (after ONLY a good cleaning but no NEW parts....hmmmm). I could technically go backwards to see if that makes a difference.
 
Hot-diggitty....just saw your link to the "Carb ReBuild How-To"..... now, I have homework to do!!!!!!
As far as new seats and needles......there are different sizes for different performance characteristics??? I'm asking....if so, what "size" is best for "recreational purposes"?
 
The diaphragms in the aftermarket kits are the primary culprit, as you want to reuse your original spring whenever possible. The aftermarket ones look the same other than the center nipple being aluminum rather than red, but they are stiffer material, and the nipple is slightly longer on most of them. This changes the popoff pressure, and can even cause the needle to stick partially open. When assembled with the correct OEM kits and the correct needle/spring/seat combination, the factory adjustment settings will be very close to spot on...
 
Dem carbs are touchy little buggers it seems.....thanks all, I'm on the path to redemption. New Mikuni kits will be ordered today!

I've sworn to my wife that the '96 will run again (as she rolls her eyes for the hundreth time).....Oh the feeling to "shut her up"....I love my wife! ;-)

At least we have 2 other skis running to keep the peace (for now!) Now all I need is a new pontoon boat! Doh!

I still find it illogical that the ski behaves on the trailer though....just doesn't seem right to me, but I'll give up....there are bigger battles to fight and for a $100.00 for a dual carb mikuni kit....'tis but a scratch!
 
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