78 Seahorse 70hp low power

[truckie292]

Hello,
I have a 1978 Johnson Seahorse 70. When it was put in the water after a year and a half of sitting, it will not go to full power. Fuel tanks cleaned, hose and pimer bulb replaced, all fuel lines replaced, fuel pump kit installed, and three carbs removed and cleaned (but not rebuilt). Runs good at wake speed and slow speed, when I place the throttle lever fully forward, runs for a couple minutes, then slowly dies back down. Any help would be appreciated.

 

[tashasdaddy]

Re: 78 Seahorse 70hp low power

vent open on fuel tank? you did not mention water pump change. check for air leaks into the fuel line.

 

[Solittle]

Re: 78 Seahorse 70hp low power

Bet you still have some crud in the carbs.

 

[Stephen_Rudy]

Re: 78 Seahorse 70hp low power

hey, funny...I had the same problem. Have you checked your fuel pump, if it is the original one, you could have some trash in it. I have a 78 Seahorse like yours and the fuel pump went bad, causing it to idle wierd as well as not go to full speed. About 2000-2500 rpm was about it then it would stall out again. You can check it by having somebody pump the bulb while it speed up, *i really do not suggest this for fear of throwing him out the back of the boat*, but if can keep it pumped up and the boat runs normal, then chances are the fuel pump is bad. Good Luck.

 

[tashasdaddy]

Re: 78 Seahorse 70hp low power

have you check compression?
three carbs removed and cleaned (but not rebuilt)
you have 3 jets in those carbs. read this.
http://forums.iboats.com/showthread.php?t=244013

diagrams http://shop2.evinrude.com/ext/index.aspx?s1=bf6ad09c53cead335fcfd8a6471c0f7f

 

[5150abf]

Re: 78 Seahorse 70hp low power

I would bet a dozen dougnuts it is your high speed jet located in the bottom of the float bowl inside the drain, pull the drain screw from the bowl, find a long skinny screw driver and stick it in the hole and get the jet out and run a stranded copper wire through it then reinstall.

Had those exact symptoms on my 50, cleaned the carb, still there, started replacing ignition parts, still there, recleaned carb and it ran like new, and the jet didn't "look" dirty but there was just enough tarnish built up that it wouldn't run right.