1978 Johnson 70hp being a bi**h

[Pappy]

That propeller is beat all to Hell.
The photo of the idle screw? If you turn that you are also throwing all kinds of adjustments out of whack. That is an idle timing adjustment only.

 

[wmk0002]

If you look in the last pic that metal piece that connects the linkage arm to the magneto is fixed length. So those screws you labeled are used to adjust the ignition timing at idle and WOT. When you adjust the bottom one it is changing the idle because as you retard the timing the rpms will drop and as you advance it they will climb. The actual idle (what opens the carb butterflies) is a separate adjustment. If you unscrewed the top timing advance stop screw in order to "open up the governor" you would be advancing the timing and, assuming timing was previously set correctly, you are prob a good bit over spec. I think you should definitely check that with a timing light. Advancing the timing too much at WOT can spell bad news especially if you pair that with a lean condition.

 

[68glasspar7870]

Anyone know where to find a used/cheap prop? This boat is a money pit, and I would like to save some money.

Also, now that I know exactly what those screws do, i will have someone drive the boat while I adjust the timing. It runs pretty good right now, but I'm not trying to break it just yet.

 

[MrGiggles]

Anyone know where to find a used/cheap prop? This boat is a money pit, and I would like to save some money.

Also, now that I know exactly what those screws do, i will have someone drive the boat while I adjust the timing. It runs pretty good right now, but I'm not trying to break it just yet.

You can't adjust those by feel or by ear. It needs to be done with a timing light. If not set properly, you'll be throwing the motor in the scrap pile.

There are many ways you can do it, but I pull the plugs, ground them, drain the carbs, and use a jumper wire on the solenoid to crank the motor remotely. Advance the controls to wide open and crank the motor to get your timing numbers, adjust to slightly under the rated WOT number. Clean up the timing marks on the flywheel and put a piece of tape or something on the desired setting, sometimes they are hard to see in daylight.

Use the Turning Point prop finder that's stickied in this forum to get an idea of the right range for your setup. Take the part number and check Ebay for a used or open box aluminum prop, usually you can them for $50-$100.

I'd say your pretty close as is, 30mph is pretty well in the ballpark for a 16-17ft boat with a 70 on the back.

 

[68glasspar7870]

Also, does anyone know what the fuel pressure is supposed to be? My fuel pump seems to be leaking a little gas and loosing prime. I would like to switch to an electronic fuel pump. I’m just not sure what size I would need.

 

[Pappy]

Just stay with the standard mechanical pump. You can potentially create one hell of a bomb with any leakage from anywhere since you have three sources for ignition within around 18" of the pump. Bad idea!