Help with timing marks?

[boatinnjax]

Help!
The timing marks on my 1990 100HP 2+2 are either gone or nearly invisible! I can just make out some numbers from left to right, 28 through 4 and then nothing but a bunch of hash marks. Looks like this:
28 24 20 16 12 8 4
..........................l l l l l l l l l l l l l l l l l l l l l l l

I've got the Seloc manual for this motor but it has no photos or description of the timing marks.
So are the 28 through 4 are degrees ATDC or BTDC?
Also, when I manually push the throttle arm to WOT the timing arm does not move, should it?

Thanks!

 

[Laddies]

Re: Help with timing marks?

With numbers in the order that you have listed they are BTDC

 

[CharlieB]

Re: Help with timing marks?

Help!

Also, when I manually push the throttle arm to WOT the timing arm does not move, should it?

Thanks!

That depends on where you are advancing the throttle, are you pushing in the throttle arm, the one with the roller that rolls on the throttle cam, linked to the timing arm connected to the throttle cable?

Try disconnecting the throttle cable and moving the arm.

Is the boat running in the water, on the hose, or in the driveway with the spark plugs out and the plug wires connected to a spark tester? (prefferred).

 

[boatinnjax]

Re: Help with timing marks?

Yes CharlieB, that is the arm I am moving. It does not matter if the throttle cable is connected or not, in either case the timing arm stays put.
No this is on the hose, plugs in, and the motor not running. I'm trying to check the timing to see if it is on or off spec.

I've been steadily improving the operation of the motor with help from you fellas here in the forum and my manual. It runs very well now, I think. This is my 1st boat/motor, so I nothing to compare it too!
I have a couple other older posts asking about fuel line routing ti all 4 carbs but have gotten no responses.

Thanks!

 

[CharlieB]

Re: Help with timing marks?

Sparkplugs out, wires connected to a spark tester, is MUCH easier on both your starter motor and battery.

Look at the throttle lever that connects to the throttle cable. Notice the linkage at the very TOP that connects the arm to the ignition timer plate below the flywheel. As the throttle is open the timer plate rotates, advancing the ignition timing, see also how the arm is linked to the throttle cam that opens the carburator(s).

Notice timing is advanced just slightly before the carbs open. I'm assuming that everything is connected and working correctly. The ignition plate is advancing to its limit and returns, not sticking or binding, no linkage broken, etc.

 

[boatinnjax]

Re: Help with timing marks?

Oh yeah, the idle timing tab is broken off the bottom of the timing arm, so the arm is always "aft" against the stop. that's why I never saw it move, I was thinking it would move "fore" not aft! Motor idled high, suppose it would with the timing advanced all the time.
I rigged a stop until I can get a new arm and set timing with assistance of e-mail from AMD (Thanks!). I've got 'er idling on a hose at 800-900 rpm. I'll get her in the water and dial it in better and set the idle screws on the carbs, then WOT test!
Hey, how loud are these old 2+2's? It is a 2 stroke so I expect it to relatively loud, i wondering about the clatter I'm hearing.

 

[airframer]

Re: Help with timing marks?

the sound could be your reed valves opening and closing. your cover is off huh? might want to make sure everything is tight just to be sure