I just took my boat out of storage after 3 years. It had been
properly winterized and laid up. To ready it for use, I paid a
mechanic to replace plugs, distributor caps, drain fuel tank, replace
filters, change all oils, and re-tune engines.

I took the boat out and ran it only to discover it would not go over
about 1300 rpm on either engine (sterndrives - Bravo IIIs) and it
backfires badly. The engines start and idle fine.

I noticed there was still fuel in the tank, almost a quarter tank
according to the gauge. From memory that could be 40 or more gallons
remaining in a 160 gallon tank. I put in 60 gallons of fresh premium
and then put in another four bottles of 104 octane boost. The problem
did not improve at all.

Any ideas? I am taking the boat back to the mechanic, but I no longer
trust him since he delivered the boat back to me in its current
condition.

Thanks.