Timing Issues 1971 Johnson 50 HP Outboard

[Kaykatz]

Hi all, I just bought this boat late last spring and it was sitting for some time. Over the winter I had the lower unit re-sealed and the carbs disassembled and cleaned, compression is 140psi on both cylinders.
O.K. my timing situation, the idle stop screw is cranked almost all the way in - it just didn't look right. I checked the timing pointer with the #1 cyl. at TDC and they line up fine. With the idle sitting against it's stop, the timing is something like 10 degrees after TDC. My manual calls for 3 degrees before TDC at idle. I've post a couple of pics with the engine set at 3 degrees.
I'm scratching my head - any ideas?

 

[Joe Reeves]

Re: Timing Issues 1971 Johnson 50 HP Outboard

The 3? BTDC pertains to the "idle cam pickup" mark where the throttle butterflies just start to open... that is the scribe mark on the metal cam is touching and aligned dead center with the carburetor throttle cam roller. This is simply a portion of the synchronization setup.


The 3? BTDC SETTING has nothing to do with the actual idle rpm. The actual idle rpm may be on that mark, under or over it, etc, due to other factors... carburetion, compression, whatever.

On many of those older models, that mechanical idle stop screw will be found screwed just about all the way in.

 

[Kaykatz]

Re: Timing Issues 1971 Johnson 50 HP Outboard

I'm confused, the manual says to hook up a timing light and adjust the idle speed screw until it reads 3 degrees.

 

[Joe Reeves]

Re: Timing Issues 1971 Johnson 50 HP Outboard

Yes, it can be confusing. I think I understand what your problem is now... I hope.

What you're saying is that with the scribe mark of the metal cam aligned with and touching the throttle cam roller, just at the point where the throttle butterflies are starting to open.... the timing should read 3 degrees BTDC BUT instead it is reading roughly 10 degrees after TDC. If so..............

Back that mechanical idle stop screw out of the way until you need it.

Temporarily remove the nylon retaining pin from the nylon clevis at the metal cam and loosen the locking nut so that you cam increase the link rod length a few turns. (lengthen or shorten... I forget which, but I think lengthen).

Now, with the scribe mark aligned with the center of the throttle cam roller, again observe the timing. It may take a few tries before you obtain that 3? mark but after you do, then you can set the actual idle rpm.

Note that the setting you're after is actually 3? +/- 1? BTDC so if you hit 2? or 4? BTDC, that's good enough.

To ease your mind about the mechanical idle stop screw... I looked in my OMC service manual at the full side view of the powerhead. The idle stop screw is set exactly like your picture, not touching anything with the scribe mark centering the roller.