Is it a carburetor “problem” or not?

[seadoo@19072]

I have a ‘94 Seadoo GTX 650. It run great.....except the speed surges up on its own when cruising about three quarter throttle. The back story is, I was having a problem with the engine suddenly shutting down when running at full throttle, but that is a different story. As a result of trying to solve that problem, I first replaced all of the Tempo fuel hoses. I removed and rebuilt the carburetors. I removed and cleaned the gas tank and fuel switch and checked the rectifier. Once I discovered the actual problem and fixed it, I doubted my carb rebuild skill and so I decided to have the carburetors rebuilt AGAIN. But this time by a technician at a local PWC repair shop. I launched and ran the Seadoo and successfully ran it through the break in period. When I hit the throttle it took off like a rocket and the stalled out. It restarted and took off but stalled out again. On the restart, I eased the throttle on and gradually went up to full throttle. It ran awhile but then shut down again. On the next restart, I eased on the throttle and then slowly ran it up to about three quarter throttle. It ran for 30 - 40 miles at that speed.......except, it didn’t shut down. Instead it would speed up on its own. After a couple of runs, it continues to react the same way. I strongly suspect that it is the carburetors. I just read the post (The Seadoo Carb Rebuild Thread by Mikidymac, April 11, 2018) and with his instructions, I feel confident that I can rebuild the carburetors. But before I do I would like some Input to determine if I actually need to go through the effort and expense of rebuilding the carburetors for the third time in less than a couple days of running time. Is it just an adjustment that is needed or a complete rebuild? Thanks for any advise.

 

[mikidymac]

Well, if you continued to run it as you said and the carbs were running lean as your symptoms suggest you could have done damage to the engine with it running then "shutting down". You could have been scuffing or seizing a piston.

Before you do anything I would check the compression (not with a Harbor Freight gauge).

If the compression is still good then yes rebuild the carbs with only genuine Mikuni parts and also replace the fuel selector and o-ring on the fuel strainer. Do not clean the fuel selectors, just replace them.

 

[seadoo@19072]

Thanks for the reply, As my back story suggests the original problem of sudden shut down was diagnosed as a lean piston seizure by some one on PWC forum. That of course led me to believe that my "carburators" were running lean. And as you mentioned, sever damage was incurred resulting in a top end rebuild by a Seadoo dealer authorized tech. Rebored cylinder and new pistons, rings ect. When I got it back I read something about the "wear ring". Looked in the pump with a flash light and saw extensive damage to the wear ring. So, I found the problem why my unit was suddenly shutting down. I replaced the wear ring. It was getting enough water to keep the engine cool when running at no wake speed but would over heat and seizeup when going fast because the impeller was not able to pump enough water through the damaged wear ring to keep it cool. After the rebuild and new wear ring I was ready for some lake time. BUT; after running it for about 30 minutes, it shut off again, kinda slowly as if it ran out of gas. It would not restart. I took it back to the dealership and he checked the compression and found the mag cylinder was shot, but the prop side was good. Dejected, I gave up. I had agreed to a "no guarantee" on the job in order for the dealership just to work on it since it is a 1994. I let it sit for a year! My wife started to get on me to get rid of it. But I decided to give it one more shot. I hate to be defeated by a machine. Never having the courage to perform surgery on a engine of any kind except for a Briggs and Stratton lawn mower class, I pulled the head and found the brand new piston had a divot about the size of a nickle right in the middle under the spark plug and a trough running to the exagust port and under the compression ring. THe cylinder was not damaged. Now what caused that? I found a local PWC repair shop who would order me a new piston and rings. I suspected that the carb rebuild that I did was at fault. I made an appointment to drop off my carbs and have him execute another rebuild. When I removed the, carbs, luckily, I left them mounted on the rotary valve cover. The mechanic discovered that one of the nuts holding the mag carb was a 13mm instead of a 12mm. Because it is a wider nut, it hit the casting of the rotary valve cover and did not draw the carb base down on the gasket and air leaked in. SO, now I am at my present problem of trying to figure out what to do. Rebuild carbs? Adjust carbs? OR sink this SOB? I will get a loaner compression tester at Auto Zone and check that out. Thanks for advise. By the way in Your carb rebuild direction post, which I found to be very encourageing, if I do another carb rebuild you mentioned that I could make my own pop off gauge, which I did by buying a bicycle air pump with a pressure gauge. I rigged it up and don't know how accurate it is. I think the book says 22 lbs but mine were popping at 19 lbs. dont know if that was a problem or not.

 

[mikidymac]

Ok, so I am really sorry about your ordeal. Sorry to say the Seadoo shop was a bunch of hacks. You never rebuild an engine unless you find out what caused the failure in the first place let alone two more times without still diagnosing the issue.

If your piston had a hole burnt in it that is from detonation caused by either running lean, timing being out of spec or them not checking the squish and installing too thin of a base gasket.

I would still check the compression before doing anything to the carbs to be sure.

The carbs are pretty easy to do yourself and between the Carb Rebuild thread and you asking questions we can get you going.

 

[AKnarrowback]

NEVER go back to those "mechanics". They don't know what they are doing.

As said, if you rebuild a burnt motor you never try to start the rebuild until you know why the motor burned up in the first place.

The divit in a piston is from detonation and is related to excess heat. Fuel mixture, timing, bad gas or squish as mentioned before. I have never heard of an impeller liner ever causing an engine cooling problem.

No guarantee on a 94 machine? They don't get much more simple than the 580/657/720 motor and parts are still abundant for doing a new or better than new rebuild. Those guys should not be in business.

Your GTX motor is a good motor, it just needs to have some TLC to the fuel delivery components and you will have a good running machine.

If you lived near by I would come by and do the work for nothing just because I hate it when a shop screws people over and leaves them out to dry.

Be patient, ask questions, there is still hope for the machine, be careful with the wrist pin bearings if you remove a piston since they are cageless and will drop parts into the crank is you are not careful.

 

[AKnarrowback]

http://seadoomanuals.net/manuals/1994-seadoo.php

Go to this link and select the shop manual download.