Magneto Timing?

My question is, "Where do I set my timing at?"
My motor is a '78 40B Mariner. It has a magneto ignition. I did enough research to finally figure out how to set timing on a magneto. I got the proper tools and set it according to the manuals specs. Well, sort of, the manual called for a dail indicator reading of 0.165 to 0.177 BTDC. The TDC mark on the flywheel was right on. There was another factory mark at 0.185 BTDC on the flywheel, so I set full advance there, because there was a mark at both no. 1 and no. 2 sides, so it would fire at axactly 180 deg. There was no decal on the flywheel to set full retard. The manual called for 4 deg. BTDC. Full advanced was suppose to be 26 deg. So, I measured the distance on the the flywheel, divided it by 26, then multiplied it by 4 to get a measurement from TDC on the flywheel, and set full retard there.
These settings were far from it's current settings, but I wasn't surprized, so far, everything on this motor has been monkeyed with. Although, I was a little concerned with the full retard setting, as I could see where the unpainted part of the stop screw was exposed, revealing a differance from factory setting.
I adjusted the throttle controls, the idle speed, and the fuel mix to these settings.
I took it out a few times. It idles smoother than ever (I also put a differant carb on). It moves though heavy seas better, giving me a better ride (I had it bored 20 over and fixed a head leak). It responds to the throttle well and does'nt wind-up like, like it used to.
What concernes me, is that I've lost 2mph. At 5000rpms it is at 25mph. The next 500rpms are very uneventfull; a whopping 1mph. I'm not that concerned with speed, but I wonder if I retarded the timing too much. I attempted to advance the timing later, but when I got everything set up, the advaced setting measured around 0.173 to 0.177(maybe that's an issue), putting it with in the manuals range. So, I did nothing, but I am still wondering where I should set the timing. I know that there is a lot going on here, but I would appreciate any help, at all, sorting this out. Thanks.

Don't concern yourself with idle speed timing--it is what it is; period. (It the motor won't idle down far enough you reduce the throttle/ timing or visa-versa.)

All you need to be concerned with is WOT full advance timing. Over the years I've learned to set this with a timing light, after removing the carb linkage (so I can safely hold the throttle weide open). Tis is the ONLY accurate way to do it, the way racers do it.

Jeff

Agree, set your max timing and don't worry about it.

As to your note about little change in your last 500 rpms - that's actually the way "it should be".

An outboard "maxes out" in the middle of it's wide open throttle (WOT) range. If the motors wot is 4500-5500, then 5000 is the peak.

(had to dig for this diagram - not something that the salesman trying to sell you the shiny new motor will point out, but explains my point above - the horsepower starts to "fall off" after the midpoint of the wot range)

Thanks everyone. It sounds like timing may not be such a big deal after all. I am courious how a magneto is set with a timing light. Could someone explain.
I did consider that I might be getting more slip on the prop. I'm running a 13P cupped. I've got a 14P ss that I'll try.
As for jetting, I'm getting some smoke at idle, and I accually went with a hotter plug because the plugs were too oily. It all seems good now.

kimcrwbr1,
I think we're talking about a differant animal. This has no window,no notch,advance screw,and no plate with numbers and marks. It just has a MAGNETO,with an adjusting ring, and two points(contacts) to adjust.

These can be a pain to set up. I don't have the specific instructions for the "b" model 40's but can give you a "in a nutshell" how to go about setting max timing.

Firstly, you set the point gap to spec. Then run the motor and check the timing against the spec setting (there was a stick on timing marker for the flywheel that you must have long lost). It sounds like you have figured where the 26 BTDC is supposed to be so if you mark it with a bit of "white out" (or the like) it will show up nicely with the timing light.

If you are "off" you need to adjust the points. Increasing the gap will advance the timing, decrease the gap will retard. You kinda horse around until you bring your timing marks into line...

Graham,
I think I'm there. Now I'm just wondering whether I should advance it more, or if it was just advanced too much before ( I was getting 28mph and now I can only get 26mph). I've been told that the motor will last longer if it is retarded by 2-4 degs, but I don't know if it hurts to have it retarded too much. Like I said before, I think it's in the proper range. I guess I'm tempted to advance it some. But not at the expence of all my work (and money).

Bear with me for a moment here.

When were you getting "28" - earlier this season (spring? mid-summer?).

Seasonal changes can knock 10-15% off your peak horsepower.

You will "always" get your best speed/performance/max horses on a very dry spring day (humidity less than 30% and temps in the 60-70 range). Humidity or heat (or both is a double whammy) will really trim back your motors performance because it's harder for it to "breathe".

It is NORMAL for a motor to lose 10-15% of it's max speed during the summer months - sometimes to the point of making it necessary to change a prop to a lower pitch (which SHOULD be done on all motors greater than 90 horses).

So all I'm saying is, the timing may not be the issue here....

I'm begining to feel at ease that all is as it should be. The diagram about the WOT clears alot of my concernes up. The seasons almost over for me here. I'll keep everything the way it is(at least this season). Thanks for all the info.
Rick