Super-jet 650 Surging at Idle, and is Running Terrible

S

SR-71

Location
Houston Texas
Hi Guys,
I have a 1991 Superjet 650 that just started to randomly act up. The Motor is Stock (except for a TDR waterbox) and has good Compression (155psi in each cylinder) and has fresh plugs that are getting good spark. Last weekend I took the ski out on the lake and it ran awesome (as it always has), then this weekend I was about to go for a ride and started it before I put it in the water to make sure everything is all right. But well for the first time ever it would barley start and once it did it was surging a lot in RPMS when idling. When I revved the Engine It did not sound very healthy. I then checked all the fuel lies and everything was tight and verified the carburetor is sucking gas. I have had the ski 3 years and never had any carburetor issues. A year ago we took the ski apart to paint it, and to service the starter. However we had to replace the stator we had the bottom of the crank case off. We did not replace the seals as they looked mint (so i dont think it is a seal). The weird thing of this is that the ski ran awesome a week ago, and has over 100 hours on it since we had the crank case apart. Oh if this helps I run the gas out of the carburetor before i put it up each time. Any ideas on what the issue could be, I'm totally lost?
 
V

Vortex

Location
Southeast
You don't have to take the crank case apart to replace the stator just remove the flywheel cover and flywheel.

Sounds like you have an air leak. Need to pull motor and pressure test. Good time to take it all apart and inspect everything, get new gaskets and seals etc.
 
S

SR-71

Location
Houston Texas
Well to make a song story short we had to pull the crank case apart to drill out the lower starter bolt we snapped off. We tried a extractor tool and then snapped that off in it so we had to split the crankcase ad found a dremmel bit that would cut tool steel, and saved the treads in the process. Sadly process of splitting the crank case we broke the stators aluminum back plate so we had to replace it.

Any Idea where to look first for a air Leak, there was no oil coming from the crank seals so? Is there any way to do this without pulling the motor?
 
V

Vortex

Location
Southeast
You need to take the flywheel cover, carb and exhaust manifold off. And then make block off plates and seals for carb and exhaust flanges or buy them from jettlab. Motor should hold 8psi for at least 10 minutes

I hope you made sure all the crank bearings were securely over the lock pins in the upper half of case before you sealed the bottom half to it. If not, you have cracked the bearings and it's time for a new crank. The best way to accomplish that is top half upside down on a bench with two holes in it for the rods to go thru while you assemble the case. This procedure is the only way to build a 650 or 701 motor.
 
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S

SR-71

Location
Houston Texas
OK cool I'll look Into doing this. Should I spend any time looking at the carburetor before I pull the engine? Because It is weird it did this massive difference from sitting just 5 days.

And I do remeber Checking the crank Shafts alignment before sealing up the crank case, plus we never pulled the crank off the top half of the engine.
 
V

Vortex

Location
Southeast
It's possible there could be a fuel delivery problem, a run away like that is usually momentary and due to starting the ski without priming the fuel system via choke/primer. I like to put the choke on and then crank the ski with start and stop pressed for a few seconds at the start of the day to help get the fuel pump(s) pressurized. Can also disconnect y fitting or t into return line, blow air into return line into gas tank until fuel comes out the other end.
 
V

Vortex

Location
Southeast
I have actually never pressure tested an engine, finally got around to making plates out of 1/4" thick steel and cut gaskets out of thin rubber a few weeks ago. Plan to pressurize thru pulse line with a t fitting to a gauge then fill with shop air and block off with a fuel line pincher at 8 psi. Not sure if that's the best way to go about it.
 

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S

SR-71

Location
Houston Texas
I tried blowing through the return line to Get fuel to come out the other line. at first it was really difficult so I flushed out the fuel filter and it flowed a little better, at most though I was only able to get a little bit of fuel to flow back through the return Nozel of the Carburetor (a very weak trickle). So I'll defiantly try this again before pull the motor. I did get a lot of gunk to flush out of the fuel filter though, so maybe something in the pump/carburetor could be plugged up (IDK). I did end up spraying premixed fuel down the intake and the motor seemed to run better so I think there could still be something with the carburetor as the problems all started all of the sudden.


Ya i do think that would be the best place to pressurize the motor for a leak down test as it would test the pressure of every gasket/seal in the motor.

By the way thank you so much for the help I greatly appreciate it. I know a good amount of stuff about these engines but by no means am I an expert (thats why I came here LOL)
 
S

Storbeck

Location
Minnesota
I would start with carburetor. It sounds to me like something is plugged. I would not expect an air leak to appear suddenly like that, but not at all uncommon for something suddenly to plug with debris or a diaphram to tear.
 
S

SR-71

Location
Houston Texas
That's what I'm thinking is the issue, I guess I'll start with the carburetor. Is there anything I should know about aftermarket carburetor rebuild kits?
 
augustaf

augustaf

Location
central florida
They are not usually even needed. Gaskets are most often reuseable. Make sure to clean the nylon "sock" inside on the fuel pump side and by all means replace your fuel filter- that might just be your problem.
 
S

SR-71

Location
Houston Texas
Sweet I'll start by rebuilding it with a genuine mikuni kit and replace the fule filter. Is there should I have to worrie about reseting the high and low speed needles exactly to what they where. I just don't want to screw something up with the settings.
 
V

Vortex

Location
Southeast
Also might want to inspect your reeds. Probably a good time to replace them with oem or some boyesen pro series, carbon tech etc for stock cages.
 
S

SR-71

Location
Houston Texas
So, after tearing apart the Carburetor and rebuilding it i was able to eliminate that as the issue. So from there I went to inspect the Reeds, and what do you know the front cylinder had had a reed petal that was completely broken off along with parts of the cage being cracked in several places. Now I just have to find where the broken reed petal ended up (good news the piston doesn't look to have scored the sleeve). Overall in the end I guess this should be the Issue, and Vortex was right about checking the Reeds.
 
V

Vortex

Location
Southeast
Told ya. I would go with some boyesen pro series reeds and new stock cages.

The PC of the Reed is likely In the bottom of crank case. You'll want to dissassemble and remove that to be safe.
 
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