1980 Johnson 70hp Seahorse

[cakopernik]

I was out on the lake yesterday and started off running great and plaining off. Got to full throttle and it started to cut out. Back off throttle a bit and it ran ok but then started to cut out again. Now when I start the motor to idle, it acts like its missing severly. Motor shakes real bad and when throttle is applied, it sounds like its trying to die. Compression is at around 130psi in all cylinders. Carbs have been cleaned and floats are set properly. Plugs are new and all coil connections are in good shape. Fuel/oil mix is 50:1. Water flow is real strong also and its not overheating. All hose connections look ok. Any help is greatly appreciated.

 

[tashasdaddy]

Re: 1980 Johnson 70hp Seahorse

time to start trouble shooting, what do your plugs look like, did you check spark on all 3 cylinders, you say you have good compression was this after it started cutting out? start with this because it is free.

 

[cakopernik]

Re: 1980 Johnson 70hp Seahorse

Out of all the things I have done, I didnt check for spark. Ill try that when I get off work. Compression was checked after the fact. Plugs were clean and dry. They are new also. I replaced them before the issue started.

 

[jtexas]

Re: 1980 Johnson 70hp Seahorse

"clean and dry", all 3? that generally indicates fuel starvation.

cylinder drop test: engine idling, pull then replace the spark plug leads, one at a time. if RPM's don't change noticeably, then that cylinder's not making power.

use a plastic or insulated tool, to avoid electrocution.

 

[Randybeall]

Re: 1980 Johnson 70hp Seahorse

Did you check the fuel primer bulb, should be soft, not sucked flat. Closed tank vent causes that, don't ask. Fuel pump, how old is the diaphgram? Sounds like fuel from the answers you have given.

 

[cakopernik]

Re: 1980 Johnson 70hp Seahorse

Well I checked the coils for spark and it seems to be pretty strong. The 5 gallon tank I have doesnt have a vent on it and the primer ball is hard after I prime it up. It doesnt get soft or suck in. The fuel pump diaphram I have not checked but will check it today. Thanks for the info.

 

[tashasdaddy]

Re: 1980 Johnson 70hp Seahorse

remove the fuel line at the carb, turn motor over, do you get gas, becareful, it it is working properly it will spray.

 

[jtexas]

Re: 1980 Johnson 70hp Seahorse

tank has to be vented, otherwise air can't enter to replace the fuel that's being drawn out, the fuel pump has to pull against a vacuum which it's not designed to do.

Is there a thumbscrew in the center of the gas tank cap? That's the vent, turn it counterclockwise to open.

 

[cakopernik]

Re: 1980 Johnson 70hp Seahorse

The cap doesnt have one. I will try to run it with the cap off and see what happens

 

[cakopernik]

Re: 1980 Johnson 70hp Seahorse

Well I tried the tank venting and it didnt help but I did notice that the airbox on the carbs was soaking wet with fuel. I took the airbox off and started the motor and it was acting like it was chugging. When I shut the motor off it didnt shut off. i had to use the choke to kill it. When I let off the choke, fuel dumped all down the ront of the carbs like the insides were full. It acts like the fuel is dumping out the front of the carbs.

 

[cakopernik]

Re: 1980 Johnson 70hp Seahorse

I ordered the manual and am picking it up today. Does anyone know if the Seloc manual shows how to adjust the carbs on this motor ?

 

[jtexas]

Re: 1980 Johnson 70hp Seahorse

Seloc is kinda confusing, but luckily, you have no mixture screws to adjust -- just 3 fixed jets. To set the float height, hold the bowl upside down - the float should be parallel to the carb body. Bend the float arm just slightly to adjust.

click over to the "engine FAQ" section of iboats & find the thread on "carb rebuilding instructions" for some good reading.