"Swing" mag or fixed timing

[Mark75H]

It took me a long time to learn the reason some guys use fixed ignition timing on modified Mercs ... I'm very certain that it came from copying what they saw on alky deflectors ... copied on the theory that if it is good for padded alkie motors, it must be good for gas mod motors, too.

The reason a lot of the padded alky deflectors used fixed timing is that they were running the timing so close to top dead center there was no room to retard the spark. If you are only running 3 or 4 degrees BTDC, there is no point in letting the spark occur after TDC for any reason.

On the other hand ... on a near stock deflector ... running 30 or 40 degrees of spark advance at WOT ... it is a lot less likely to pop back and "bite" you if you can set the spark back to 10 or 15 degrees while pulling the rope.

Some racers have tried to justify running fixed timing as a real improvement by saying keeping it at a constant setting improved accelleration. If you look at the way the Merc linkage works you will see that there isn't much time that an old Merc spends on the race course with the timing other than at full advance: as you close the throttle from full to pretty much closed the timing is still against the full advance stop.

[JohnsonM50]

Ive gottem the impression that [speaking of 2 cyl - MK25,20 or OMC 22s etc.] That to be sure the points would be 180 degrees apart [when right] it needed to be locked to ensure they stayed right. Thats not a problem with CDI because of the pick up coil tho.

[Skoontz]

With any 2 cylinder OMC, you place a factory timing fixture on the crank, disconnect the ground for the coil, put one lead of a test light on the points, and the other at ground. When you move the crank pointer into the hash marks on the mag plate, the light will go off because the points just broke. If you want to advance timing, you drill a hole in the brass strap that pulls the mag plate ahead of the one the factory set. We used to make straps with incremental holes.

[Fast Fred]

some race motors (other than merc) came with fixed right out of the box, witch
the factory made special parts just to set it up fixed, thay could have more easily used the swing, why would you suggest thay went to the trouble.

No, i have not worked at that factory.

[mercury400m]

the omc's mag adv. are fairly equal to the carb but 95% of the idle is mag advancmentment and the top end mostly the carb

the brass peices are adjustable arn't they? just have to use a 5/16 socket to loosen both very small nuts and you can advance a decent amount but still having the motor to be able to run or are you talking about a different brass piec b/c i know there are a few. also what hp roughly are you mentioning some were a little bit different.

[Skoontz]

the brass peices are adjustable arn't they? just have to use a 5/16 socket to loosen both very small nuts and you can advance a decent amount but still having the motor to be able to run or are you talking about a different brass piec b/c i know there are a few. also what hp roughly are you mentioning some were a little bit different.[/QUOTE]

The early V-4 50, and 75's were adjustable, and that trickled into the 40 twin. By the time the 40 got that ridiculous compression release added (which was the first thing you tossed away in a tune up) the brass strap had two drilled hols that were not movable with out drilling more hols. 40 and under had a pressed in pin which went through the strap on the bottom of the flywheel plate and a stainless cover snapped over the pin then locked with a couple tabs that were formed into the piece. Nothing under 40 HP ever had an adjustable slide, except maybe, just maybe the pre 1956 36 cubic inch 25's At least if my blonde hair is not over riding my common sense memory.

[jeff55vDSH]

It took me a long time to learn the reason some guys use fixed ignition timing on modified Mercs ...

Interesting theory Sam.
I never saw any reason to "lock" the mag on my 4cylinder mod Merc. Although, it would have made the throttle setup a lot easier. The LAST thing I wanted was that thing to kick back while roping it over. Once I got overzealous with my Mod that wouldn't start. I opened the throttle nearly all the way, and that in turn, advanced the timing all the way. The thing kicked back, ripped the rope from my hands and shot it 50 yards out into the river! OUCH! :mad:

[JohnsonM50]

The 31.8 ci OMC s I mess with have 3in. pistons,, they can hurt ya when advanced to start.

[mercury400m]

lol jeff i bet you still felling that one today =p=p (so far mines been nice to me ...keyword SO FAR)

ok i understand now what brass piece your talking about now. didn't most
40's have a bent up clock spring that went through a hole and other side hooked on to a pin???? if im totally wrong let me know

[RichardKCMo]

Both of those can hurt a 10 yr. old if advanced past the start on the dial.
I don't know the degrees , but i know how much shorter
it makes your arm feel, next bay.
rfkcmo

[RichardKCMo]

Hey Johnson, what's so special about those 35s?
RichardKCMo.

[JohnsonM50]

Not much... an easy motor to keep, lots of parts available, alot of tork, they last a long time and perform well. Could be said about alot of motors, maybe I like em is the best answer. My runnabouts on the heavy side and the tork works well there. My hydro is about C weight and that motor seems to work well at 68 to 7000 Rs [its meant to run 5500]

[Skoontz]

The old 35's....Dad made one with dual carbs and opened the ports, ALOT. He added reed blocks that dropped into a manifold, and got rid of the old OMC flower pedal style reeds because they were too restrictive...Then, he took a C quicksilver gearbox off a puked Merc that came in on trade, cut down a tower, and ran it on an old Speedliner or Sid service runabout, I fogtot which, but it had the rear kneel pad with an open mid section....
It routinely turned 7K, then after he started tweeking rods (had a few cast and forged at a local foundry), he started turning up RPM. I remember that motor twisting 8-8500 and then his next challenge was having props cast, because he could not get a big enough pitch for what he was looking to do.
Excellent engine virtually unkillable, and, one that every family boat from mid fifties to 60's had clamped on the back.

Then came the 40's off the same platform...Different story all together. Thinner rods, at least initially for a few of the early years, and a much rougher idle....I called them the pukamatics....

[mercury400m]

ur talking about good old omc johnson evinrude right??? i have a old 35 viking that im trying to track down a lower for that turns out great rpm more than it says

ps skoontz you would have a pic of that 35 ur dad made sounds friggen awsome :D

[Skoontz]

that there are all these cool memories of the West Side Boathouse and I only have few pictures. I wanted the ones of the Rockholt/4-60 and that old dual carb OMC. If I had 3 engines, I could very easily make another one. I watched him do it very closely, and with all the people on this forum now who have foundry access, it could be done much more efficiently. This motor never made it to a hydro, but imagine a 2 cylinder C mod, about 9 full inches shorter and 43 lbs lighter than a 4 banger Merc. Then add alky into the mix.....

[mercury400m]

hmmmm sounds like a future project.....;)

[RichardKCMo]

Not much... an easy motor to keep, lots of parts available, alot of tork, they last a long time and perform well. Could be said about alot of motors, maybe I like em is the best answer. My runnabouts on the heavy side and the tork works well there. My hydro is about C weight and that motor seems to work well at 68 to 7000 Rs [its meant to run 5500]

What are you getting out of it for speed?
Richard

[JohnsonM50]

What are you getting out of it for speed?
Richard
Richard, In an HK Airborn at 460lbs [me in it] It topped at 54.8 gps so far. In a C- Bezoats with a 25 [31.8ci] that went 63 so far. I think the runnabouts near the top of is game but think the hydros got room to go. these both are on -lefty feet-

[JohnsonM50]

Interesting theory Sam.
I never saw any reason to "lock" the mag on my 4cylinder mod Merc. Although, it would have made the throttle setup a lot easier. The LAST thing I wanted was that thing to kick back while roping it over. Once I got overzealous with my Mod that wouldn't start. I opened the throttle nearly all the way, and that in turn, advanced the timing all the way. The thing kicked back, ripped the rope from my hands and shot it 50 yards out into the river! OUCH! :mad:
Im using Quincy visu-matics and found with my MK25s and OMCs the throttle doesnt have enough thro, leverage or return spring to work well moving the mag and carb.

[jeff55vDSH]

Im using Quincy visu-matics and found with my MK25s and OMCs the throttle doesnt have enough thro, leverage or return spring to work well moving the mag and carb.

You're right. I had tomodify my throttle lever a little to get more travel. I modified the deadman's throttle. The slot that the lever moves forward and back inside, I cut that slot a little longer. I think I needed about 3/4 of an inch. I also think I added a spring on the mag to increase it's return power.
This was on a 4cylinder Merc.
Back when when I ran 2cyl mercs, I manually advanced the stator after I started the motor. I just had my throttle linkage on the carb.
Sorry if I'm a little fuzzy on this, I'm on some serious pain killers right now. :(

[kampenracing]

Jeff how are you feeling after your crash on Sunday. It looked like a pretty hard one. Did you do any damage to the boat or motor? I hope your felling better.

[jeff55vDSH]

Jeff how are you feeling after your crash on Sunday. It looked like a pretty hard one. Did you do any damage to the boat or motor? I hope your felling better.

I just made a pass on the inside. I wanted to make the pass stick. I went into the corner too fast. Hooked the boat, and it shot me right out. I think the throttle jabbed into my ribs pretty hard. But they say nothing's broken. I find that hard to believe. I start watching the clock to count down my pain med time. I lost the engine cowling, broke a coil mounting bracket. broke the right cockpit side badly.
I'll get better. The boat can be fixed. I can buy engine parts at the Tohatsu dealer near my house. I'll be back.
I'll never race again without flack protection under my jacket! Heck, it's mandatory next year anyway.
Thanks for the well wishes!
:)

PS. I'm fast. But you guys are fast AND great drivers! I have a long way to go to reach the driving level of all of you guys.

Oh, sorry to hijack the thread. BTW, the spark advance "swings" on my Tohatsu.

Here's a pic taken just moments before my little crash:

[RichardKCMo]

Does that mean there will be more than 1 tohatsu at centralia?
I can't wait to see how bad those old 40 mercs whoop em this year.

RichardKCMo

[jeff55vDSH]

Does that mean there will be more than 1 tohatsu at centralia?
I can't wait to see how bad those old 40 mercs whoop em this year.

RichardKCMo


What's Centralia? Is that a boat race? I don't see it on the APBA race schedule.
And, you mean they still race those old 40ci Mercs? I thought APBA dropped the 40ci class when Merc came out with the 44xs way back in...what was it, 1988? Sorry, I'm not very good with the vintage/historical archives.

[David Mason]

What's Centralia? Is that a boat race? I don't see it on the APBA race schedule.
And, you mean they still race those old 40ci Mercs? I thought APBA dropped the 40ci class when Merc came out with the 44xs way back in...what was it, 1988? Sorry, I'm not very good with the vintage/historical archives.

NBRA silly. Not APBA. I know we almost had you talked into coming to the races last year for them, you just were not quite ready with the rig yet.

Take some more pain meds.... hehehehhe. Get well. Looks like you were on the inside of my teammate Shaun O'Leary in the 13M in that pic. Hope you at least gave him a bath on that pass !! Would love to see that Tahatsu on his boat, I bet if would be a killer combo.

Yes, NBRA still runs the old APBA Mod structure, the D is 40CI Mercs, and E is the 44CI Mercs. Super E is the big motors. (OMC, Yama, Tohatsu, etc) For the stocks, your APBA legal D Stock is a legal D in NBRA (40CI) class. Shaun is going to the NBRA Nats with his 44XS D stock to compete in the D class. I can't wait to see if he can beat the old man. I got my money on my dad right now.... if we can get the old girl back together. She suffered some damage a couple years ago when the mag hanger broke and advanced the timing instead of retarding it... dangit all. And those certain pistons are very hard to find, very very hard. Can find Merc pistons all day.

[jeff55vDSH]

NBRA silly. Not APBA.

Sorry for the smack talk. Can I blame it on the pain meds?
Yes, The 40 mods would be a handful. The 44 mods at the APBA North American Championships were a handful for my lil' Tohatsu too! If there were a good driver behind my wheel instead of me, I think the Tohatsu would'a won it. But now I'm just playing armchair quarterback eh?
I'd better go take some more pills.

[JohnsonM50]

Sorry for the smack talk. Can I blame it on the pain meds?
Yes, The 40 mods would be a handful. The 44 mods at the APBA North American Championships were a handful for my lil' Tohatsu too! If there were a good driver behind my wheel instead of me, I think the Tohatsu would'a won it. But now I'm just playing armchair quarterback eh?
I'd better go take some more pills.

Glad to hear, it sounds like your getting better.