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1972 100 HP Johnson timing adjustment

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xj287

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I'm helping a friend resurrect a (free off craigslist) 1972 Johnson 100HP motor.100ESL72R. Runs ok but the ignition timing is WAY over advanced. Where is the adjustment? I spent about an hour on it today and couldn't find anything that would retard the timing. Any ideas?
 
Full throttle spark advance is the only adjustment. The timer base bangs up against the adjustment screw at full advance. It is a long screw with a rubber cap, starboard side, behind the top end of the vertical throttle lever. Spec is 28 degrees at full advance @ 4500 RPM in gear, on the boat on the lake. Or with a test prop.
 
im suspecting that the rotor may have spun on the crank shaft.....it "idles" close to 40 deg BTDC, and the full throttle bump stop would need to be almost 4 inches longer then it is.......so something is definitely out of whack some where.
 
If it idles smoothly the timing is not that far out!-------Review timing marks or make your own with # 1 at TDC
 
DOES NOT idle smoothly, runs, but idles at close to 2500 rpm any throttle what so ever shuts it off. spark timing is deffinetly WAY out of spec. i'll be getting back on the project a little later on today and ill dig a little deeper then
 
well, im running out of ideas.........runs great, idles and revs smoothly only if I limit the timing lever travel by replacing the bump stop with a 3.5 inch bolt
 
You do have the spark plug wires on the correct plugs, right? And in the right towers on the dist cap? I'm also thinking distributor rotor. Or somebody managed to somehow screw up the timer sensor's rotor. Easy to guess from here but hard to know.
 
here's an update.......I extended the bump stop with a 3" bolt and got the motor to run very well. however, once the boat had run out the lake for an hour or so, the timing seemed to go back to normal so the original bump stop had to be put back in. over the weekend the timing fluctuated back and forth a couple times between 40 deg. BTDC (at idle) and normal (27 deg WOT). so now im wondering could a defective pulse pack to the root cause
 
as a last resort I called my local boat dealer this morning to pick their brain on the problem......they've always been so helpful in the past (and I've spent about $30,000 there over the last 20 years) they were no help and even acted like I was inconveniencing them by even calling there for parts! wow, I guess I'll get all my parts online from now on.
 
xj287 said:
as a last resort I called my local boat dealer this morning to pick their brain on the problem......they've always been so helpful in the past (and I've spent about $30,000 there over the last 20 years) they were no help and even acted like I was inconveniencing them by even calling there for parts! wow, I guess I'll get all my parts online from now on.
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Yeah, nobody wants to work on those anymore for a couple of reasons. #1, their techs don't know how. #2 they are afraid they'll get two or three hundred $$ (or more) into it and you will tell them to take it and do you-know-what with it. Looks like you are stuck with learning how to fix it yourself, or find an old-timer that knows how. Or go out and spend mega-bucks for a new motor.
 
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