Troubleshooting technique

[brynifer]

1998 150 hp saltwater Series v6 twostroke. Noticed power loss at cruising speed, drops about 200 rpm but will come back but then drop again. The lower speed is consistant, as though one or more cylinders is dropping out and coming back. Spark plugs all show good combustion. To narrow down the problem I removed the throttle linkage between the carbs and from idle, opened each carb one at a time. Top and bottom carbs increased rpm. The middle carb slowed the motor down and stalled it if I allowed it to. Question is, is this a valid troubleshooting technique. It is telling me that I have a problem somewhere with the two middle cylinders, be it fuel, ignition or reed valves.. Any thoughts?

[ausnoelm]

Probably not the best method, that said, saying it is spark or fuel just about covers everything that could be wrong.

[brynifer]

I ended up removing that middle carb and when I checked the float, I found it way too hi when I measured it. Actually , i did'nt even have to measure, it was no wheres near the correct setting. I know there was or is an issue with the today's gas attacking fuel contact components in outboards. How about what ever the float needle is made of, rubber, silicone, has swollen to the point that it is throwing the float level off?