1971 Johnson 50 hp - exhaust relief valve

[Kaykatz]

Can any body tell me if there is a way of testing the exhaust relief valve to find out if it's working properly? I bought the Johnson manual but can't find testing procedures in it. It starts easily with muffs but I took it to the lake twice and could not get it started when I backed the trailer in the water. The plugs got flooded the first time, so I replaced the plugs. I also removed the carbs and couldn't find any trouble there. Float hieght is fine, the needle is sealing properly - no wear on it at all, and there was absolutily no dirt in the bowls. I also put fresh type C gear oil in the lower end. I'm planning on replacing the waterpump & impellor over the winter but I'd like to find out if I have to do any repairs on the exhaust relief valve.

 

[Willyclay]

Re: 1971 Johnson 50 hp - exhaust relief valve

Welcome to the forum! The experts here, which I am not, can help you with any problem. While I do not have any experience with your particular model motor, most outboards do not have a "valve" in the exhaust relief outlet. It should be a direct opening into the exhaust housing, so I am not sure what you are thinking about replacing. Item #84 in the parts diagram for your motor at the link below is a "cover". Possibly yours is blocked by trash or critter deposits like the dirt dobber nests I removed yesterday from my motor. Good luck!

http://www.marineengine.com/parts/j...&manufacturer=Johnson&section=Exhaust+Housing

 

[Kaykatz]

Re: 1971 Johnson 50 hp - exhaust relief valve

Thanks Willy, I'll check for blockage when I drop the lower unit. I thought there was some kind of solenoid or valve that operated that passage way.

 

[boobie]

Re: 1971 Johnson 50 hp - exhaust relief valve

What's the compression on it ?? Will the spark jump a 7/16 " open air gap on a spark tester ??

 

[F_R]

Re: 1971 Johnson 50 hp - exhaust relief valve

Just thinking out loud, when you are trying to start it on the trailer backed into the water, just how deep is the motor in the water? The exhaust relief ports on the backside of the midsection below the powerhead do act as a "valve" or place for the exhaust to escape when starting. If they are deep in the water, it MIGHT have the effect you are thinking of. But I dunno, I sort of doubt it.

I'd rather suspect a worn-out motor. How's the compression? OR improper starting procedure. You are setting the fast idle/warmup lever on the remote control.....aren't you? I was along on a friend's maiden voyage of his brand new boat and he couldn't get it started for the first time. I reached over and lifted the fast idle lever, and it started immediatly.

 

[Faztbullet]

Re: 1971 Johnson 50 hp - exhaust relief valve

I'd rather suspect a worn-out motor.

+1
Those engines are bad about skirts wearing out on pistons but still having good compression...

 

[Kaykatz]

Re: 1971 Johnson 50 hp - exhaust relief valve

This is my 1st boat so I don't have a routine starting procedure but it starts easily on muffs. I put it on high idle, turn the key 1 click, lift the choke toggle and turn the key all the way. I have not done a spark or compression test - I guess I should start there. Right now the carbs are off - is it advisable to do a compression & spark test now? Also when I backed the trailer in the water the exhaust relief was well above the water line.

 

[F_R]

Re: 1971 Johnson 50 hp - exhaust relief valve

You can do a compression test with the carburetors removed.

 

[w2much]

Re: 1971 Johnson 50 hp - exhaust relief valve

Not sure here but is that an electric shift? If so is type C lower unit lube correct? Correct me if I'm wrong but I don't think you want type C oil in an electric shift LU

 

[Kaykatz]

Re: 1971 Johnson 50 hp - exhaust relief valve

O.K. I just did the compression test and I got right around 140 p.s.i. on each cylinder. I did the spark test set @ 7/16" gap and both seemed fine. I may be grasping at straws here but is it possible for the coils to have an intermittent problem?

 

[Joe Reeves]

Re: 1971 Johnson 50 hp - exhaust relief valve

Not sure here but is that an electric shift? If so is type C lower unit lube correct? Correct me if I'm wrong but I don't think you want type C oil in an electric shift LU

The 1971 50hp model is a Hydro Electric Shift engine and demands "Premium Blend" gearcase lube, also known as "Type C". Nothing else will do.

 

[Daviet]

Re: 1971 Johnson 50 hp - exhaust relief valve

Your compression and spark seem to be good, have you tried to adjust the low speed needle valves in the carbs to see if they are set correctly? Might be time to overhaul the carbs.

 

[Kaykatz]

Re: 1971 Johnson 50 hp - exhaust relief valve

I have the carbs apart now - just waiting for the carb kits to arrive. I guess I'll just have to wait till spring to see if that solved the problem.

Thanks All for your input.