1984 50hp johnson seahorse won't accelerate

[duffg130]

Hi,

I recently bought a 1984 sea nymph with a 1984 Johnson 50hp Sea Horse. The motor fires right up but when I accelerate the motor bogs down. I'm probably only going about 15 mph when this happens. I am going to rebuild the carbs. Any thoughts on what else I should do? In the meantime I swapped out the motor and put my 2009 25hp yamaha on the boat. The boat does 20mph with the 25hp on it. Any idea how much faster it will be with the 50 johnson on it? I love the reliability of the yamaha and just not sure if I want to put the time and money into the johnson. Is 1984 a good year for that motor? Thanks in advance for any advice.

 

[Bosunsmate]

No Title

Yes they are a good motor, ive got the 82 which is basically the same. They kept the same design for many years as they work just fine apart from one main issue which is to do with cooling. You must move the telltale outlet from the bottom of the exhaust cover up to the top of the water jacket. Otherwise air accumulates and she will overheat at lower temps.
Heres a thread on it
http://forums.iboats.com/forum/engi...aq/228380-johnson-evinrude-adding-a-tell-tale
I did mine right on top of the engine as that to me is the most effective spot for it.

 

[Bosunsmate]

You could do a drop test on each cylinder and also check that each cylinders spark jumps a 7/16 gap
If that doesnt show anything up you will probably need to do a compression test and then also check timing

 

[bonz_d]

Those are fantastic engines, Just sold a 1975 50hp, have a 1983 60hp on my boat right now that is waiting to be swapped with a 1987 50ph that has power tilt/trim.

Start with a compression test, should be 140 -150lbs on both, then do a spark test. then move to the carbs. I would suggest not running it too much as-is because if there is a carb that is not working properly there will be a lean fuel condition on that cylinder and you could end up burning a piston.

 

[duffg130]

Thanks. I'll start with those. I think the carbs are the only thing I can do myself. Not sure about the rest.

Those are fantastic engines, Just sold a 1975 50hp, have a 1983 60hp on my boat right now that is waiting to be swapped with a 1987 50ph that has power tilt/trim.

Start with a compression test, should be 140 -150lbs on both, then do a spark test. then move to the carbs. I would suggest not running it too much as-is because if there is a carb that is not working properly there will be a lean fuel condition on that cylinder and you could end up burning a piston.

 

[duffg130]

Maybe I spoke too soon. I just looked up the compression test and spark test. Those are easier than rebuilding the carbs. I'm also going to move the telltale like Bosunsmate suggests.

 

[bonz_d]

Maybe I spoke too soon. I just looked up the compression test and spark test. Those are easier than rebuilding the carbs. I'm also going to move the telltale like Bosunsmate suggests.

Neither of those tests are difficult and only take a few minutes. Should be able to pick up both testers at any of the auto parts stores for about $30.00

 

[duffg130]

I did a cold start compression test today ( carbs are off the motor). I only cranked the key until the gauge stopped. 140 psi in both so I'm good there. I'm assuming I should've had the carbs on and fuel entering the cylinders? Thanks

Neither of those tests are difficult and only take a few minutes. Should be able to pick up both testers at any of the auto parts stores for about $30.00

 

[bonz_d]

Compression sounds good. Check spark?