71 50 hp Johnson stalling at higher rpms

[ryane87]

So I had issues with getting my outboard to idle and stay running and finally broke down and rebuilt the carbs. Now the boat runs and idles much better but at higher sustained rpms the engine will seem to lose power and kill itself. I was also having issues where I would be on the water and have the throttle wide open and be moving very slowly (probably around 10mph). I did take the cover off the engine and verify that the throttle was wide open at the carburetor. I figured I had a fuel issue so I rebuilt the fuel pump, changed the screen out at the fuel pump, replaced the fuel lines, line from carb to carb, and the line from the cylinder to the fuel pump. I also cleaned the screen filter out that is attached to the fuel line that drops into the fuel tank. I put a fresh tank of gas (6 gallons gas, 50:1 mixture marine 2-cycle oil, and 6 oz Seafoam) in (the other gas was pretty new but just to be thorough) and continue to have issues with the engine dying at high sustained rpms. Also the boat still refuses to really accelerate when on the water even with the throttle wide open.

Any thoughts??

https://www.youtube.com/watch?v=4_ecH0tjol0&feature=youtu.be

Above is a video I took. I am sitting in the back of the boat because I was trying to watch the fuel going into the carbs. I know I probably shouldn't be running the engine this hard on muffs but I am trying to figure out what the problem is. The beginning and end of the video demonstrate the issues best. In the middle I was kinda playing with the throttle.

 

[ryane87]

I am going to ask a potentially dumb question but I just stumbled across this. How much would not having the plugs on the air silencer cover affect the fuel to air mixture at higher RPMs? I just happened to be browsing through some schematics and realized there are two rubber plugs that cover the low speed needle adjustments. They did not come on my engine so I never realized they were supposed to be there. It seems to easy to be the solution to a much larger problem but I figured its worth asking.

 

[97fordrunner]

I have the exact same engine the plugs not being there should not affect the performance at all. Also its not so much running hte High RPM on Muffs a tank isnt any better its about free revving the motor with no load which can cause it to grenade. I'm not sure why yours is flat out shutting down at high RPM thats a new one on me for sure it doesnt sound like a fuel issue since there really isnt any bogging out. Seems more like an ignition issue where spark just stops like the key is being shut off. Not 100% what would cause that, how is the head temp? I know these have a temp sensor but believe its only wired to an alarm not a safety shutdown.

 

[ryane87]

The engine killing itself happens when on the water (under load) on on muffs. I noticed it first on the water because I don't typically run the engine on the muffs long enough (or rev it up much). The power pack was replaced due to a spark issue and the plugs are new. The plugs are Champion UL77V which is the recommended plug for this engine. I did recently hear that Champion are garbage. Should I be using a different plug?

The head temp is ok. I haven't checked the actual temperature but you can lay your hand on the engine above the plugs. It's warm but won't burn you. There is plenty of water circulating on the muffs. The hot horn does work and will go off if the engine does get too warm (accidentally burned up an impeller a couple months ago). There is no safety shutdown.

 

[ryane87]

I am going to put the rubber plugs into the air box to see if that makes any difference. I still would like to know anyones input on the spark plugs mentioned in my post above. I am really at a loss here if I can't get this going..

 

[97fordrunner]

I read somewhere else on here that said NGK were the worst. Spark plug preference is just that when it comes to old motors.

 

[ryane87]

UPDATE:

Since posting this I have installed the rubber caps over the low speed needle adjustments, changed the spark plugs to Champion QL77JC4. I have also replaced the primer bulb as a piece broke off inside of it (or came loose).

Still having problems with the engine bogging down. It won't accelerate over an estimated 10mph and has to be held at a crawl otherwise the engine will kill itself. When not running under load the engine can be revved quite a bit more. I have noticed that the primer bulb (even the new one) seems to get sucked down a bit. I tried cracking the gas cap and it seemed to help. Within the last couple weeks the filter at the end of the gas line (in the gas tank) has been cleaned and the fuel hoses replaced and carb and fuel pump rebuilt. When the engine is started cold and initially put in gear there seems to be a small surge of power and then immediately slows back down. I can (when the engine is running within the first 5-10 mins open the throttle up all the way (throttle is open on the carbs all the way) but I really am not going over 10 mph.

Any suggestions would be appreciated. Video below shows the boat on the water. I had the warm up throttle up a bit because it was bogging down. Later on I figured out that if I keep it at a real slow pace I can set the warm up throttle all the way to run and just crawl along. I did note that the engine was pretty warm. Took the cover off and the top was hot to the touch (could place my hands for 2-3 seconds before having to remove it). The hot horn did not go off (I know it works). The engine is definitely circulating water. Is there a thermostat that regulates water flow through the engine that might need replaced?

Again any help would be appreciated.

https://www.youtube.com/watch?v=mdaBu5K8-eA&feature=youtu.be