I have an MLM 6904B wizard, 1964, 3.5 hp. Apparently the exhaust is released into the water. After I have run it awhile a thick oil slick develops ontop of the water in the testing tank. What would cause such a thick oil slick? I am running with a 50:1 mixture using a small engine two cycle oil.
Is there a trick to setting the timing on this outboard. I downloaded a "how to" from freeengineinfo.com but wondered if there is a recommended technique from those who know. Like what to lookout for, or be careful when doing this.
The oil slick is going to be expected with the older outboards. Actually, if I am not mistaken, the old McCulloch-made engines (which is what your Wizard is) of that period should be run at 24:1 vice 50:1. I have noticed an improvement in using synthetic blended 2-cycle outboard oil, but they are going to put out some sludge. It is especially noticeable when you run them in a bucket. Make sure you are using a TCW3 marine-rated oil, and not just any old two-cycle oil.
You may see some improvement in setting the carburetor high/low mix needles (could be running a little rich), but you need to do this on boat while motor is running under load to truly set the carburetor properly.
To set the needles, start with the high-speed needle first. From all the way closed, back it out (counterclockwise) 1 turn. Back the low speed (idle) needle) out 1.5 turns from all the way closed. Start 'er up and get it running at wide open. It will run rough. In quarter increments, continue to open the high speed needle, giving the motor time to adjust after each quarter turn. You should see improved performance. Do this until the motor starts to "sneeze" (i.e. too lean) and then bring it back clockwise one-quarter turn. This will be your optimum setting. Then, bring the motor down to idle and repeat the same process with the low speed needle. Again, do this on the boat, not in a bucket.
Bottom line, don't be too alarmed about the slick.