info on a 1978 johnson

[scarboni]

Hello all, i have a 1978 35 hp johnson seahorse. I was wondering if anyone could give me some info on this motor. Like gas to oil mix and maybe a suggestion on what prop would be best. It currently has a plastic prop on it. And I don't think that I am getting the speed that I should be getting. The boat is a 78 alumacraft fishing boat. Any info is appreciated.

 

[rickdb1boat]

Re: info on a 1978 johnson

Hi Scarboni

50:1 is the correct mix for your motor. 1 pint of tcw-3 outboard oil per 6 gallons of gas. You should also be using Champion plugs QL77JC4 gapped at .030. As for the prop, I really can't say what pitch would be best. It depends on the Wide Open Throttle RPM's you are getting now and the current pitch of the prop. Odds are you don't have a Tachometer hooked up right now, so that makes it all the more elusive. But taking a quick peek at the prop selector says that if your boat weighs around 500 pounds(Light), then a 10" X 13" prop would be a good starting point. If you find that your boat is heavier or lighter, then you may want to consider going up(Lighter) or down(Heavier) in pitch..Best I can do for now...What model Alumacraft do you have?? Kingfisher 14 or 16 footer?? What speed are you getting or is it by the seat of your pants it feels slow??

 

[scarboni]

Re: info on a 1978 johnson

Thanks for the info. No I don't have a tach. The boat is a Alumacraft Lunker 16'. I am just guessing but I would say that it weighs more than 500 lbs. It has the "bass boat" type stuff inside. Two fishing chairs, console and passenger chairs, livewell, lots of storage compartments.
I don't know the exact speed I am getting, feels like around 15 mph, but I really don't have anything to gage that on. Somebody is going to let me borrow their GPS the next time I go out so I can tell how fast I am going.

 

[tashasdaddy]

Re: info on a 1978 johnson

you really need to know the wot rpms, this is how you set up and outboard, not mph. borrow an induction timing light hook it up the the top plug and run it wide open and register your rpms. i don't have a manual for your motor to tell you what your optimum, rpms should be, sorry. may someone else can. find out what you have presently, and then adjust to get to the proper rpms.

 

[Bob_VT]

Re: info on a 1978 johnson

If you go to nadaguides.com and look up the value of your used boat .... the dry weight is listed (minus the engine, fuel, accessories) and it gives you a good reference point.