Timing w/out test wheel - Update

ED21

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Aug 26, 2003
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I have a 40 hp '89 Johnson that I want to check the timing on. The manual say to do it with a test wheel only.<br />Given the obvious safety issue of speeding along w/ the engine going 5000 rpm & pointing a timing light at the flywheel, will timing it this way be accurate.<br />Or should I just let a shop do it.<br />Or get a test wheel which I assume costs to much for the limited use it will get.
 

Joe Reeves

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Feb 24, 2002
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Re: Timing w/out test wheel - Update

Ed.... I don't know if that engine has the "Fast Start" feature or not, but if so it will need to be disabled to do the following timing procedure.<br /><br />Perhaps other will have the knowledge of the above and also the knowledge of how to disable it if it exists.<br /><br />With that in mind, you can time your engine as follows:<br /><br />(Timing At Cranking Speed 4°)<br />(J. Reeves)<br />The full spark advance can be adjusted without have the engine running at near full throttle as follows. <br /><br />To set the timing on that engine, have the s/plugs out, and have the throttle at full, set that timer base under the flywheel tight against the rubber stop on the end of the full spark timer advance stop screw (wire it against that stop if necessary). <br /><br />Rig a spark tester and have the gap set to 7/16". Hook up the timing light to the #1 plug wire. Crank the engine over and set the spark advance to 4° less than what the engine calls for. <br /><br />I don't know the full spark advance setting your engine calls for, but to pick a figure, say your engine calls for 28°, set the timing at 24°. The reasoning for the 4° difference is that when the engine is actually running, due to the nature of the solid state ignition componets, the engine gains the extra 4°. <br /><br />If you set the engine to its true setting at cranking speed, when running it will advance beyond its limit by 4° which will set up pre-ignition causing guaranteed piston damage! You don't want that to take place. <br /><br />No need to be concerned about the idle timing as that will take care of itself. The main concern is the full advance setting. <br /><br />Be sure to use your own engines spark advance settings, not the one I picked out of the air here in my notes.
 

ED21

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Re: Timing w/out test wheel - Update

Not sure about fast start, it's a tiller model, but I will check.<br />Is the spark tester put on both plugs so as not to burn out electronic ignition & no compression for good cranking speed?<br />Thanks for the info. It sounds a lot easier & safer than hanging over transom.
 

tvpear12

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Aug 25, 2004
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Re: Timing w/out test wheel - Update

may i ask why 7/16"? that is a very wide gap compared to the actual plug gap..437 to be exact.
 

rodbolt

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Sep 1, 2003
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Re: Timing w/out test wheel - Update

cause the manual specifies 7/16th. under compression that .035 gap looks a lot bigger to the spark. it insures that the system is capeable of correct voltages without any flashovers.<br /> good luck and the only way to verify WOT timing is on a test wheel, a dyno or at wot going acrossed the water.
 

tvpear12

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Aug 25, 2004
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Re: Timing w/out test wheel - Update

hey rodbolt, you are saying you cant set wot timing with out a test wheel, and joe reeves is saying you can and describes how. i am now more confused then ever. I brought my timing light home to do what joe reeves said, the you say you must have a test wheel.i am the dumb one and you guys are the smart ones, but we have 2 top dogs saying 2 diff things. whats up with that? after all the main topic is timing with out a test wheel.
 

seahorse5

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Jan 24, 2002
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Re: Timing w/out test wheel - Update

Joe's way of setting the timing will get you close, especially if you are putting together a motor from a rebuild. The only accurate way to set timing is to make sure to run the motor, under load of a test wheel, dyno, or on the water, above 5000 rpm according to service manuals. <br /><br />There are many types of electronic ignitions and each will have different changes in timing from cranking rpm to WOT rpm with the timer base in the full advance position.
 

ED21

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Aug 26, 2003
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Re: Timing w/out test wheel - Update

Well I set the timing per Joe's advice, except for wiring the advance to the rubber stop. I don't think I have that. <br />I just advanced throttle all the way. My original timing was advanced 3d from where I now set it.<br />The boat runs like a bat out of hades & real smooth up to 5400 rpm. There is absolutely no way I could ever check timing at speed, even if I could see the timing light in the sunshine.<br />The back story as to why I wanted to check the timing is that the throttle cable & linkage was all messed up & the throttle was only opening about a third of the way. I was only getting about 4500 rpm w/ a crappy hole shot.<br />Now all 40 horses throws the boat up on a plane in seconds. <br />And I caught a big fat catfish on a split spinner to boot. A fun day was had by all.<br />Thanks for the help. Maybe the timing instructions should go in the FAQ.
 
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