The Online Magazine For Amateur Boat Builders

Obsolete Outboards
by Max Wawrzyniak

Start to Finish, Book II:
(Part 1 - Part 2 - Part 4)

Reviving a Vintage Big Twin - Part 3

Another Saturday, and another opportunity to spend several hours on the Big Twin, after an early morning 2 hour paddle in the Larsboat on the near-by Meramec River.

click to enlarge
(click images to enlarge)

The first thing that I did was to remove the magneto that I had previously re-mounted; not due to any problems, but because I had decided to make the installation of a lanyard equiped safety shut-down switch the subject of a future column, and the Big Twin would serve as a guinea pig for that. So the magneto was removed and some alterations made and a few photos taken and then it was remounted.

click to enlarge One may have noted that in the previous part of this column, I made no mention of setting the "gap" on the ignition points before testing for a spark; this was not an omission in my writing. I just forgot to adjust them. That the ignition system would still produce a spark is a testament to it's reliability. After reinstalling the magneto today, I did remember to adjust the point gap to .020, using a cheap feeler gauge and a regular screwdriver which are the only tools required.

The flywheel was then installed and torqued and the recoil starter remounted.

I make it a habit to always replace the fuel hoses on any engine that I am "refurbishing," and the Big Twin was no exception. The only hoses on this - pressure-tank-utilizing engine are the hose which conducts the pressure from the crankcase to the "quick connect" fitting, and the hose from the quick connect fitting to the carburetor which carries the fuel. Although this engine had a fuel strainer incorporated into the carburetor, I added a small "in-line: fuel filter as well, which is my habit.

click to enlargeFinally, the adjustment synchronizing the ignition advance to the carburetor throttle valve was made. On most of these old OMC's this is no more complicated than loosening a tapered "cam" and moving it back and forth until the throttle valve begins to open when the valve's "follower," which rides on the cam, reaches a certain mark on the cam. No "diagnostic" computer needed.

What WAS now needed was a solid mounting surface in order to attempt to start the Big Twin, and the AF4 provided that; the Big Twin was clamped to the transom with it's "leg" submerged in water in the plastic 55-gallon drum that serves as my outboard motor :"test tank." The low- and high-speed mixture adjusting needles were set at about 1 full turn open (not the correct setting it turns out) and I commenced to "yanking" on the starter rope of this manual-start-only engine.

click to enlargeAfter a few pulls, the thing actually started, coughing and wheezing as it blew smoke and water in large quantities; some fiddling with the mixture controls settled it down a bit, and I left it running at a fast idle while I took a few photos. Then the thing coughed on last time and quit. I cranked it over several times, then several times more, and then some more, but it would not start.

I made some adjustments to the mixture needles and pulled the rope some more and it still would not start.

A few more adjustments, then some tries with the choke off, then with the choke on, then with the mixture needles screwed-down shut (in case it was flooded) but nothing would coax the engine to fire-off.

It is at this point in the process that people tend to become irrational and end-up yanking the starter rope until they are blue in the face, or end up grinding away at the electric start until the battery is dead, or until the starter motor overheats so bad that it throws it's solder all over itself and self-destructs.

After about 10 minutes of attempting to start an engine that had been running just moments before, I decided it was time for some trouble-shooting. since numerous adjustments had already been made to the carb with nary a hint of an intention to run again, I decided to check to see if the magneto was still working. Removing the spark plugs and grounding them to the engine block revealed no spark when the engine was cranked. The recoil starter was removed and the flywheel slowly rotated by hand, revealing a slight"clicking" or snapping noise. Could be a spark jumping to a "ground," or could be something hitting the flywheel. Since I was careful to check for any interference with the flywheel when I mounted the magneto, I could not believe that there was a problem now, but I drug out the flywheel puller anyway and removed the flywheel.

click to enlargeAs I lifted the flywheel off, I immediately noticed that one of the condenser' wires was broken off; evidently the flywheel magnet caught it and ripped it apart. That would prevent one cylinder from sparking, and while a properly turned 2-cycle, 2-cylinder engine will often run on one live cylinder, the Big Twin had only been running for a minute or two and was far from being "in tune."

I replaced the damaged condenser with one from my stock, and also rechecked the point gap setting (as one should always do whenever the magneto is disturbed,) and "buttoned-up" the engine again, making darn sure that the wires underneath the flywheel were routed well clear of rotating parts.

click to enlargeA few more pulls on the starter rope and the engine fired-up again. A few minutes of running showed that the engine was most likely ambitious-enough to keep running for a while. It also was pumping cooling water well, although after several minutes the discharge water began to heat-up to the point that it was almost too hot to keep one's hand in the stream. An outboard run in a bucket can overheat very easily, however, so while it is an item to check carefully during the engine's first run on a boat, at this point I will not consider it a problem.

Tomorrow I will haul the AF4 and Big Twin down to the launch ramp on the Meramec River, where the park gates are unlocked at 7:00 am but the gentleman who collects the ramp fee does not arrive at work until 8:00, leaving me with a one-hour "window of opportunity" for a free launch.

On to Part 4