From your description, the power loss and backfire is a lean-out
condition, and not ignition related. If the engines idle fine, the wires
are on correctly and since the plugs, caps, etc. are new, no crossfire
in the distributors likely. More likely: fuel related; clogged jets in
the carbs, bad fuel pumps from sitting so long, clogged water separators
or filters (including the screen in the carb inlet). Really bad fuel,
although more likely a delivery/metering issue. Unless your mechanic
actually had the boat out on a run after servicing, don't blame him.
Take it back and let him resolve the problem. These problems are the
result of letting it sit so long.
JR

wrote:

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.



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