Johnson 50hp bog out and die above half throttle

[Captain Bravo]

It is a 50ESL73R It was (supposedly) rebuilt a few years ago. When I first got this engine it ran great for about 20 minutes. Then it started losing power at higher throttle settings. Now it will bog out and die above about 1/3 to 1/2 throttle. It will start and run fine at idle and high idle. But about the time it should really come into it it dies out. Sometimes but not always feathering the choke can make it run a little better.

I have replaced a leaking stator, rectifier, went through the carbs (even though they looked like new inside), replaced all the fuel lines. I can't check the compression at the moment, my tester is at a friends house, but it feels good. What can cause something like this in light of all the parts I have changed?

 

[F_R]

Make sure the spark is advancing before the carburetor throttles open. (Sticky timer base). If it doesn't advance before the carburetors, it will fall flat on it's face.

 

[Captain Bravo]

I know the timer base isn't sticking. I forgot to mention earlier that I replaced the trigger and cleaned and lubed the timer base to make sure it had free and smooth movement. I hadn't thought about the linkage possibly losing adjustment. I'll check into that. Thanks.

 

[Captain Bravo]

Timer base is definitely not sticking. Linkage all looks good and moves freely.

A guy I work with said that his golf cart lost power at higher throttle when a crank seal went bad. Could a crank seal cause the issues I am having?

 

[Captain Bravo]

Everything I check on this engine is perfect. Last night I had it on the lake and it would stay running at full throttle, but it didn't have any more power than half throttle. Timing is perfect, throttle is opening all the way, compression is 155# both cylinders. I don't know what else to check.

 

[Captain Bravo]

Well, I still don't understand it, but it is running a lot better. Another mechanically inclined person (my dad ) came over and I showed it to him. I had dismissed the fuel pump because I had bypassed it and hand pumped the primer bulb while someone else drove, and it did not run any better. He just started with the manual and ran through the whole series of tests. While I worked on his trailer he read and tested. In the end, we removed the check valve from the top of the fuel tank, cleaned the fuel pump, and adjusted the float. Why that worked I have no idea, but there it is. I thought I would update this just in case any one had a similar issue.

 

[Captain Bravo]

Well that was short lived. Took boat out tonight and it ran great for about 15 seconds leaving the dock and then it bogged down and started doing exactly the same thing it did before.   

 

[Quick3201]

Please post your cure when you find one. I have 1980 50 hp Johnson with same problem. I have been following your Dad's process of elimination. Good luck!!