Thread: Mercury Mark 40-H

  1. #1201
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    ..."The initial timing is set by the box at 7 degrees. This holds until the engine reaches 400 RPM. Makes for easy starting. I have started with both an electric starter and the good old rope. No issues. I then add the initial timing set at 20 degrees advance which comes in at 1,000 RPM and then between 1,000 RPM and 3,000 RPM I add an additional 25 degrees to give me a total of 45 degrees. Remember a standard Mark 55-H has a factory setting of 42.5 degrees advance. After 3,000 RPM I start to remove 8 degrees of timing until were at 8,000 RPM. After that we at 37 degrees until max RPM for our engines which is about 8,600 RPM. "

    This, of course, could easily be done with the old magneto!

    Right!

    Jeff

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    Team Member A/B Speedliner's Avatar
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    Jeff
    Explain how to vary the timing with the magneto while you are under way. If you rigged up a secondary lever to change advacnce separate from the throttle position. The magneto was found to vary RPM by a few hundred due to either belt stretching or slop in the belt and pulleys.

    David
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    Default Magneto vs Electromotive system

    With the normal factory magneto setup the Mercury design would swing the magneto with throttle setting. Once your set at full throttle the magneto is fixed at the set advance. When we are running in the MOD classes most racers fix the magneto at their desired settings. This is an issue when starting the engine in that you have all the advance in at cranking. A lot of folks will tell you how the engine kicks back if you don't set up properly for the start. With the Electromotive system the starting spark advance is close to what you have when the mag swings. With a two cycle cross flow engine the engine needs less spark advance at full throttle compared to when the engine is accelerating. The electromotive system allows us to back out spark advance when were at high RPM to optimize the engine power. This could be done with a separate magneto control but would not be as effective as the electronic system. Also the driver can drive and not have to be an engine manager.

    Alan

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    I was kidding, David!

    What Alan is accomplishing with electronics is nearly impossible to do the 'old way'. That's the beauty of it.

    Jeff

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    Theoretically, you could set the butterflies to be open completely before the mag hits the stop and give yourself some wiggle room by backing off the throttle a bit. From a practical point of view I couldn't see myself remembering to back off the throttle a bit in a race!

    That's a neat system. I'm not sure I'm smart enough to figure out where to set the timing in degrees though. Especially different timing at different RPMs. I ran my C at .350" and my E at .300" and that worked well for me. Tried everything from .300" to .375 on my D and never really did get dialed in in that class. I doubt that timing was the problem though. Motor ran clean, just either all top speed with little acceleration or decent acceleration and not enough top end. Props and setup... I ran my B at .180" (per Paul Christner) but that motor was padded. I raced B hydro only 2 years and B runabout 1 year. I got the runabout running better than the hydro. At best the hydro was a middle of the pack finisher. The runabout would do a little better. The Mercury just wasn't competitive with the Hot Rods day in and day out. I tried a locked mag for a bit on the 4 cylinder motors but not for long. The B was locked.
    David



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    Sounds like your D motor could have used Alan's magic ignition system with its endless programmability.

    Automotive engineers spend man-years trying to find the best spark advance/ fuel air ratio at every speed/ throttle/ load condition their engines see. It's exhausting work, but that's what makes one engine perform (power/ fuel economy, etc.) a tiny bit better than another one.

    I suspect a D motor needs more spark in accelerating out of the corner, and advance less advance down the straights (to prevent detonation?) Here's where electronics can pay dividends.

    Jeff

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    Default Electromotive ignition test with timing light

    The electromotive timing disk is setup to have 60 equal pads for the magnetic sensor to read. That means that there is one every six degrees. There are 60 equal gaps so you have one ever six degrees also. Saying that we have a resolution now of three degrees. There are two teeth missing that allow the electronics to figure out where it is relative to crankshaft position. I intend to mark the flywheel with little dots of white paint and then use a timing light to view the advance action taking place. I will try to record this on video to look at later. It is also possible to use a volt/ohm meter to read the timing right off the box. By using the two methods I will have a way to validate the actual advance setting. This is a cross check on how good our mechanical positioning is. Once verified I will only have to use a meter to verify timing. Electromotive also has a nice tool to help set the unit up without running the engine. There pulse simulator feeds the box and I will use the meter to verify the settings at the desired RPM. All fun stuff when you start looking at how to optimize an engine. We will soon water test up at Alexandria on a weekend with a couple friends. David L-6 your invited if you would like to see the testing.

    Alan
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    It has been our experience with running Electromotive ignition you need to ck.initial timing frequently,it can change quite a bit. Especially after installing on a engine that has just been reassembled. After all the heavy assembly grease and oil burns off. There is lots of slack in the Merc rotating assy. Vibration seems to be a factor also. You also need to experiment with sparkplug heat ranges and gap. Lots of surprises there. We have been running this system for the past 3 yrs and are still learning.
    Art K

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    Very interesting indeed! On the Mercury 1250 125hp inline six, the distributor was setup to retard the timing at w.o.t., and I believe it was the only engine with the "Thunderbolt Ignition" distributor to do this.

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    Default Season is getting close.

    We have been working on getting ready for the 2014 season and have made a number of changes. Besides the electromotive ignition system were developing we have switched to the Yamato hatchet running one under gears. Doug Kay has set up our Brinkman housings so that we can run a Merc or Yamato by detaching the two water hose feeds and four bolts. I have two D MOD engines and will run one with a magneto and one with the Electromotive system. I will have two Roskowski D MOD boats nearly identical. I intend to run one with the 1 under Merc unit that I now have mounted on the test engine. Should be a fun test session. So I will have a side by side comparison of last years setup and what we will run this year.

    Alan
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