Danny,
That misfire seemed to be somewhat intermittent, so I think Red18's lean idle mix theory is a good one; a bad coil would probably give a continuous misfire. However I'm not sure if your carbs have an idle mix adjustment screw. My 115 had fixed jets for both low and high speed circuits. As a pretty mildly tuned motor, it always had a real smooth idle, but it would misfire whenever I had a clogged low speed jet, which is a possibility if motor sat for more than a month or so with fuel in carbs, especially with premix fuel. Don't know about your motor but both the low and high speed jets were easily accessible W/O removing the carbs on my old V-4! There was a brass screw that covered each high and low speed jet, so just pull the brass screw and look in there with a good light to see if it's plugged; you can remove the jet with a small screw driver or just stick a wood toothpick into it to clean it. Just be careful not to drop any of the screws! Maybe put a rag underneath to catch anything that drops! You might have to remove some of the throttle linkage or fuel hoses to get to all of them. A service manual should show the location of the jets/access screws and tell you which one is the low and high speed jet.
Before you start screwing with the carbs I'd suggest you make up a spark checker to keep on the boat for troubleshooting, like I did for my old 115 based on a picture in the service manual, to see if you have a weak coil. Here's what I came up with, which I think is an improvement on the service manual tool:
1. Get a big PVC cap . . . I think I used 2" for the V-4; you might want to go to 3" for a V-6; spray paint the inside of cap with flat black paint to make spark more visible in bright sunlight.
2. Get 7 1/4-20 SS machine screws about 3" long with threads the entire length of screw.
3. Drill one hole in center of cap using a No. 7 or 13/64 bit, and tap for 1/4-20 threads (make sure hole is SQUARE with top of cap!); get a long piece of wire, put a big alligator clip on one end and put a 1/4" ring terminal on other end. (I used a solid 14 ga piece of copper house wiring because it's stiffness helps support the whole works when you're testing). Install one screw in center so it extends into cap with the wire terminal underneath it on outside. This will be your ground electrode.
4. Drill 6 equally spaced holes (every 60 degrees around outside circumference) in side of cap, about 1/2" from end of cap; tap holes for 1/4-20 threads.
5. Cut heads off the 6 remaining screws.
6. Install the 6 screws into cap; adjust so that there is a 7/16 gap between them and the center electrode. Use a 7/16 nut (which happens to be the size that fits a 1/4-20 machine screw) as a gage to set the gap. Make sure you have at least on inch or so of screw protruding on outside of cap at all 6 locations.
7. Pull all 6 spark plug leads and attach them to each of the 6 screws sticking out of side of cap (the 1/4" screws are just the right size for plug leads to make a good connection); attach ground lead to a good ground on motor.
8. Turn on water to flushing attachment (Don't even crank the motor without feeding water to pump, to protect impeller!), and have someone crank motor while you watch cap for a spark jumping gap at all six locations.
9. If you don't get a spark on a cylinder, you may have a bad coil on that cylinder; if no spark on one bank of cylinders, you may have a bad power pack on that side. A healthy ignition system will typically throw a spark over a 1/2" or larger gap, so if it won't jump at least a 7/16" gap, something is wrong!
This test checks the entire ignition system, from sensor coils in the stator assembly that trigger the capacitor in the power pack, to the power pack and coils. It's a simple test that I used to run whenever I was planning to run offshore after the motor had been sitting a long time. Good luck with the trouble shooting! Denny
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