75 Stinger is a Stinker

I have a '77 Jetster boat with a '78 Johnson 75 Stinger. Won't run on the lake.
Starts up with a flick of the key...(on land in a tank)...sound great, runs smooth...revs up.

New water pump.
New fuel lines...ALL fuel lines.
Clean and synched carbs.
New plugs.
New fuel tank.
New prop and seals...(oil and exhaust)
122 psi on each cylinder.
Here's what it does:

Starts up on lake at the dock.
Warms up.
Shoots water.
Pulls away from dock.
Push throttle forward and it moves at trolling speed in half throttle position.
Pushing to full throttle it starts to bog...then it chokes and dies.
Restart...does same thing.
Any help would be greatly appreciated.
Thank you all...in advance.

 

Bear in mind that when out of the water, and under no load, motors can sometimes rev out freely, even with impediments. You really need a workshop manual and consult the troubleshooting area, but it sounds like a fuel delivery issue, maybe the fuel pump isn't working properly, even a chance the gauze trap that catches debris is clogged. If the demand for fuel exceeds supply, which can happen under load, but not show up when running unloaded, naturally things come to a halt. Also check the choke, if it has one ( some old Johnsons that era did) to see it isn't sticking.

 

99% the carb rebuild was not a success.
1% that there is a problem with the spark advance system. The bottom half of the throttle movement is virtually all advancing the ignition. Only from that point is the actual throttle advanced. If the ignition stays retarded the engine is never going to make any power.

I have had main jets and various air passages completely blocked by fuel varnish. In some cases main jets completely blocked by corrosion from water attracted by ethanol in the fuel. I think the OP needs to go back over the carbs and make sure everything that can be removed is removed and every passage checked to be sure it is clear. Use carb solvent and a ultrasonic cleaner, might take several rounds to get all the crap off.

I have had issues similar to described with my Tohatsu 9.9 2 stroke, Suzuki 2.5 4 stroke, Seadoo SPS jetski, Stihl Weed whacker, etc etc

 

The 75 was a three cylinder engine with three carbs, which makes me doubt it is a carb problem, the thing would be well down on power with one carb not functioning, but would not "die".

 

Okaaaaaaayyyyyyy.....!!!
Waiting for replies and reading MEGA FORUMS, I finally solved the problem.
Having cleaned all three carbs and putting on new gaskets...
I failed to check each carb for fuel flow.
Number one carb had no gas.
Took it back off and checked the bowl. A piece of old rubber fuel line was wedged between the needle and fuel feed sleeve.
My bad...I did NOT clean the debris from under the float bracket. That still had several pieces stuck to the hinge.
Cleared...cleaned and reassembled. Checked for fuel flow. Thumbs up....
Replaced on engine and fired her up. Wow! Sounded more beefy.
Took it to Mardon and launched.
Started right up.
Let it warm up while I parked my rig.
Still running when I returned.
Pushed off and threw it in gear.
With much hesitant reserve I pushed the throttle forward and holeee smokes...that Stinger flew like a bird.
Planes outrun under 20 seconds at full throttle. Ran around the lake for about a half hour...
Extremely pleased with this engine.
Thank you for advise and replies. This is a great forum site. I will be sticking around to read up on other issues if they come about.
Happy cruising to all.

 

Deteriorated fuel line debris was stuck in Top needle valve.
No fuel delivery. Empty bowl.
Works like new now.
Full power and running at about 6500 RPMs.
Thanx for reply.

 

Fixed the problem...she screams to me.
"Let me fly!"
So...she did.

 

Good to hear, but I'm still puzzled that it would "die" under load, assuming you mean stop dead, if two carbs were fully functional, I'd expect it to just labour and not get the boat up on plane.

 

Apparently the number one carb and cylinder are the key to power up with the factory engineering on this particular motor.
I read mass posts on many forums and everything was pointing at the carb.
Yes...it didn't just big down...it flat quit. Then was hard to start on the lake.
Not today. Double check everything before reassembly.
My bad...