73 Johson 50 hp

[erbey]

I have a 1973 Johnson 50 Hp Motor. I have done everything to it - including replacement of power pack, rectifier, coils, fuel pump, in addition to rebuilding the carburetors. Finally got it run. It starts up with starting fluid -runs for a little while with me holding the throttle in a midway to high position. Within about a minute or two it dies on me. It almost acts like its running out of fuel. If I spray starting fluid it starts up again but doesnt last. I noticed that the primer bulb also becomes flat. I tried moving the fuel tank really close it to limit the length of fuel line suction since I have a 12 gallon tank located in the middle of the boat but that did not work. When I removed the carbs I noticed that you could see daylight through one of the leaf valves. I am wondering if the engine is not creating sufficient suction to make the fuel pump diaphram work. The engine has good compression - 110 on both cylinders. Any ideas - I am about to give up on it and buy something newer.
Appreciate any advice. Its not heating up because I disconnected the sensor.

 

[tashasdaddy]

Re: 73 Johson 50 hp

"I noticed that you could see daylight through one of the leaf valves" did you remove the reed valves, that is the only way you could see daylight, and a small gap is acceptable.

 

[tx1961whaler]

Re: 73 Johson 50 hp

Start systematically troubleshooting the motor:
Check the compression.
Check the spark on all cylinders with a spark tester
Make sure that fuel is getting to the carbs. A primer bulb flattening out is an indication of an obstruction in the tank, fuel line, connector, or tank vent. If you can get or borrow another tank and fuel line, do it.

 

[erbey]

Re: 73 Johson 50 hp

I have done what you said already - using the process of elimination. I verified that I have spark - verified with a spark plug wire tester. The fuel tank is new. The fuel lines are new. Yes I removed the reed valves to clean them - and that is when I seen a tiny gap in about two of them. The manual says they are suppose to be perfectly seated and not to apply hand pressure to them. Either way I thank you both for your advice.

 

[tx1961whaler]

Re: 73 Johson 50 hp

Is the fuel line/primer bulb assembly an after-market Attwood brand, by any chance?

 

[erbey]

Re: 73 Johson 50 hp

Yes its an Attwood brand - is that a problem? If it is let me know and I will change it.

Tomorrow I am going to try something different. I might have been leaving the vent closed on my fuel tank. I have been opening and closing the vent as I have been working on it. I will take the gas cap off tomorrow and try it - just to make sure the suction on the fuel pump is not trying to pull a vacuum on the tank.

 

[jay_merrill]

Re: 73 Johson 50 hp

First, no more starting fluid! It has no lubricating properties, so you need to put some premix in a spray bottle and use that.

Since the motor wants to run when you spray fuel in the carbs, and the bulb collapses, it seems obvious that you have a fuel delivery problem. If you had not mentioned that you opened vent for sure, I would have suspected it as your problem. I would go ahead and remove the tank cap tomorrow and see what happens. If the motor runs OK, there may be an obstruction in the vent. If not, I think my next area of suspicion would be the fuel line/primer bulb assembly.

Let us know what happens!

 

[erbey]

Re: 73 Johson 50 hp

It ran a lot better today with the gas cap off and I put a new primer bulb on it. Its still dieing after it runs for a little while. I think my settings are off - not sure how to set the timing on it and throttle adjustments. I am just going to take it on to a marine service company and get it checked out. Thanks for all the help.

 

[jay_merrill]

Re: 73 Johson 50 hp

That's a good idea. You will probably find that your service manual calls for a reset of the timing if the power pack is replaced. I've replaced them without retiming, but doing so is recommended.