1978 75HP Johnson full throttle issue

[PISTONESAL]

Hello,

I have a 1978 Johnson 75HP outboard motor. I am curious what happens to a motor when the gas tank almost empty. Yesterday, I went out and when I tried to go full throttle the engine sounded strange and the motor would not go at the normal full peed. The RPM's were at1500 at full throttle. I have 2 6 gallon tanks and the one it was hooked to was just about empty. I moved the gas line to the other tank which was full. I hooked it up and did the same thing. After crcling around in 100 feet circles, the motor then went to normal speed. CAN the tank being almost empty cause this issue. Please let me know.

Thanks

Sal

 

[fireman57]

Re: 1978 75HP Johnson full throttle issue

Running out of gas just makes you have to prime it to restart. I would do a spark check on each plug because it sounds like you have a coil going bad. Look at each plug wire where it goes from the plug back. It will go into a coil, one for each plug wire. Look closely at them for cracks or goo oozing out of them. The spark you are looking for will be bright blue and make a loud crack. you can pick up a spark tester at any getyourautopartscheap store for about 10 bucks. Yellow or orange spark is not good enough. I think your coils are around 20-30 bucks and you can get them right here.

 

[PISTONESAL]

Re: 1978 75HP Johnson full throttle issue

Fireman,

Thanks for the reply. the engine would start but when I opened throttle it would not speed up. After circling around I tried it again and it was fine the rest of the outing. Going out of gas can't/ would/nt cause this?

Thanks

Sal

 

[fireman57]

Re: 1978 75HP Johnson full throttle issue

Shouldn't.

 

[SKEETR]

Re: 1978 75HP Johnson full throttle issue

It is also possible that you picked up some water in the bottom of the first tank and it took a bit to pass it through the carbs. Are you running any other filtration besides a inline particle filter?

 

[PISTONESAL]

Re: 1978 75HP Johnson full throttle issue

Thanks for the replys guys. Well, I went out yesterday again. It did the same thing where it would not speed up. I pumped the gus bulb. It was a little soft, but it still didn't go and then it did. I am woring I may get stuck someday. I have already removed, disassembled and soaked carbs and that was only a few moths ago. It has been running like a champ. After it starts working, it doesn't do it again the rest of the outing. I will have to see if it does it again on the next outing. Any idea, suggestions,thoughts? I appreciate any help.


Thanks

Sal