Condensation in tank?

[Phil Layer]

My inboard has become harder to start and the idle is rough. It backfires a bit when I hit the throttle. However, once the rpm's are up, it runs great. Timing is spot on. Plugs are newer. New coil.

I suspect water in my fuel. How do I test for this?

Also, if water in the fuel is causing the problem, can I run it at higher rpms until the bad gas is burned out? If not, I will have to pump the gas out of the tank and that will be a major job.

[Dinikin]

I only have one suggestion. Seafoam.
I will Pm you a link on how to use it.

[Orca]

Pull your filter, dump it in a glass gar. If no water seperates out after 10 minutes, then you don't have a water problem.

Points or elec. ignition? Carb or FI?

Back-fire is lean, timing or ignition problem. Rough idle is carb, vacuum leak, or ignition problem.