Request clarification Re: Joe Reeves WOT timing procedure

[JarFisch]

1) What *precisely* is the purpose of incorporating the 7/16" spark-gap setup prior to performing the Reeves timing procedure? -- I mean, what effect does the size of the spark-gap have on the timing parameters? ((why wouldn't we want to use the operating gap (.030) of the actual plug used during normal engine operation?))

2) On the current motor I'm dealing with (J90TLEOR) there isn't a rubber-tipped max-advance stop screw as found on earlier 70's engines and referenced by the J.Reeves guide. -- Instead, there is a thumb-wheel nut (and jam-nut) on the spark-advance rod which connects the timer base arm to the throttle lever. -- So it's somewhat unclear to me as to how to follow the Reeves' description for setting "maximum-advance" of the timer base prior to cranking and checking with a timing light. -- In other words, should I run the thumb-wheel nut all the way out to it's limit and start from there?... or perhaps do something different than that?

Thanks very much,
charlie

 

[Tim Frank]

Using the 7/16" spec with a spark tester verifies that your ignition system is operating properly.
If it isn't, any timing adjustments are a crap shoot.

 

[eavega]

1) What *precisely* is the purpose of incorporating the 7/16" spark-gap setup prior to performing the Reeves timing procedure? -- I mean, what effect does the size of the spark-gap have on the timing parameters? ((why wouldn't we want to use the operating gap (.030) of the actual plug used during normal engine operation?))

The 7/16" air gap is the equivalent to a .030 gap under compression. If the spark can't jump the 7/16" gap in the air, then it won't reliably spark under pressure in the cylinder.

2) On the current motor I'm dealing with (J90TLEOR) there isn't a rubber-tipped max-advance stop screw as found on earlier 70's engines and referenced by the J.Reeves guide. -- Instead, there is a thumb-wheel nut (and jam-nut) on the spark-advance rod which connects the timer base arm to the throttle lever. -- So it's somewhat unclear to me as to how to follow the Reeves' description for setting "maximum-advance" of the timer base prior to cranking and checking with a timing light. -- In other words, should I run the thumb-wheel nut all the way out to it's limit and start from there?... or perhaps do something different than that?

The point is to advance the spark as much as possible (i.e. what it would be at WOT) and HOLD IT THERE. The timing measurement needs to be done with the spark advanced as far as it will go when the throttle is pushed wide open. I wouldn't change anything before taking the timing reading. Once you have established whether you are in or out, then you mess with the spark advance.

In fact, here is a post from Joe Reeves answering a similar question on a similar motor

That model at the dull spark advance timing simply has the vertical slotted arm holding the timer base in place. The flywheel magnets, when the engine is running, is forcing the timer base linkage back solidly against that slotted linkage. It DOES NOT incorporate the timer base stop screw.

By pulling the timer base further and wiring it as one would do with a engine that has the timer base stop screw, you are advancing the timing further than it should be. As such, you are setting up a pre-ignition condition which will actually result in at least one melted piston!

Redo that procedure having the engine at full throttle/full spark advance position via the vertical slotted arm but DO NOT try to advance the timer base any further than what the slotted arm takes it to.

 

[sutor623]

The purpose of the gap tester is to allow the motor to spark WITHOUT starting. If you simply disconnect the spark plug wire from the spark plug you may not get a spark (meaning timing light wont flash) and you will damage your ignition components.The key has to be in the ON position for this procedure to work. It also allows you to make sure the motor is producing enough spark to accurately time the motor (as suggested above.)

I would leave the WOT timing stop where it was and check first. You may not even have to fool with it.

Look at part #2 on the page on the right. That is the WOT stop screw. Simple stuff.
http://www.boatinfo.no/lib/evinrude/manuals/1992-2001johnsonevinrude.html#/66