Setting wide open throttle timing: Mercury v. Evinrude

Repair or modification of Boston Whaler boats, their engines, trailers, and gear
pcrussell50
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Setting wide open throttle timing: Mercury v. Evinrude

Postby pcrussell50 » Mon Jun 01, 2020 12:49 pm

I started in boating 12 years ago now with carbureted, two-stroke-cycle Evinrudes, whose manuals specify running the motors at full throttle with a timing light and adjusting the timing linkage to read the specified timing advance. Dangerous and cumbersome.

Later, back in about 2015 I got my first Mercury. Also carbureted, two-stroke-cycle. Only Mercury, in its repair manuals, specifies setting the wide open throttle timing while cranking the motor using the starter. Much less dangerous and cumbersome.

In the meantime, a prolific and well regarded member in the online boating community, Joe Reeves specified a method of setting timing on Evinrudes, the easier and safer way that Mercury does, by setting it while cranking on the starter.

Question: is setting the spark advance really that easy? Sounds like it should be, as long as you can correlate or map the number you set cranking on the starter, with whatever it is supposed to be at full throttle out on the open water. Am I missing something here?

-Peter

biggiefl
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Re: Setting wide open throttle timing... Mercury versus Evinrude

Postby biggiefl » Mon Jun 01, 2020 2:23 pm

Unless you rebuilt the engine, there is no need to check or adjust the timing, especially on conventional two-stroke engines.

Modern four-stroke-power-cycle engines have a crank position sensor, just like cars, and there is no need to adjust timing. The engine computer computer does it for you.

I have owned outboards for 40 years. I have owned probably 100 outboards and I have NEVER adjusted the timing on any of them and NEVER blew up an engine due to it.
On my 24th Whaler. Currently in the stable: 86 18' Outrage, 81 13' Sport(original owner), 87 11' Sport, 69 Squall. :roll:

pcrussell50
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Joined: Fri Oct 16, 2015 1:08 am
Location: SoCal/SoNev

Re: Setting wide open throttle timing: Mercury v. Evinrude

Postby pcrussell50 » Mon Jun 01, 2020 3:21 pm

biggiefl wrote:Unless you rebuilt the engine, there is no need to check or adjust the timing, especially on conventional two-stroke engines.


On my Mercury, when I changed the stator and timer base, I had to unscrew the linkage to the timer base. You also have to do this if you are going to remove and adjust the throttle cam. I suppose if you meticulously counted threads before disassembling the linkage, you could get it back together pretty close.

-Peter

jimh
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Re: Setting wide open throttle timing: Mercury versus Evinrude

Postby jimh » Tue Jun 02, 2020 6:51 am

I have a vague memory of checking the timing on my 1992 Evinrude 225-HP V6 engine. I borrowed a "test propeller" from my dealer. The test propeller is a specialized propeller that creates a load but does not produce any thrust forward. The boat was tied to the dock in a boat slip in a private marina where I was renting the slip for the weekend.

I used my old Heathkit timing light. It was a very bright timing light so you could easily see the strobe effect even in strong direct sunlight. (With a not very bright timing light you would need the flywheel to be shaded and not in the sunlight.)

With the engine running at very high speed--I do not recall the exact RPM but it was probably at least 4,500-RPM or more--the test propeller was creating a huge flow of aerated water around the propeller, and the engine noise was very loud. I remember a few other boaters came over to see and ask what was going on. I never repeated that test.

The spark advance timing in a two-stroke-power-cycle engine is very influential on engine speed. As I recall, the engine spark advance was created by actually mechanically rotating the position of the stator coil assembly a few degrees around the crankshaft. The coil was mounted on a plate that was lubricated so it could remain free to move.

The low idle speed of the engine was primarily controlled by the spark timing. As the throttle lever was advanced, the dual mechanical linkage created immediate movement in the spark timing by rotating that coil assembly and the with more movement of the throttle the butterfly of all the carburetors began to open. At some point, the rotating movement of the stator coils ended due to the design of the linkage cam, and thus so did the spark advance, while the carburetor butterfly valve continued to open.

Before setting the timing, you must verify the position of the scale that is the reference for the flywheel mark used to denote timing . You are supposed to use a special tool to measure the exact position of the piston in a particular cylinder to be at the absolute highest point of movement. The accuracy that of that affects the accuracy of the timing measurement.

I don't have any experience in how accurately the wide-open-throttle spark advance could be verified without running the engine at high speed. I guess the assumption would be there was a fixed correlation between the spark timing, but that seems like it would assume that the linkage and cams were all in perfect adjustment. I think the reason for checking the timing at high speed is to verify that the linkage and cams are in proper adjustment, and that the stator coil plate can rotate to its intended full-throttle position.