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backfires, no power under load, merc 350s

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.

STAN_MUTE
May 19
I agree. Fuel is the most likely culprit. There just is no good way to store a gas engine 3 years. One thing is for sure after three years it can gum up just about the whole thing. jamesgangnc
May 21
There could be any number of issues here, but it may be something really simple.

And your mechanic should be given first crack at fixing it - he did the original work - give him a chance to make it right.

Short
May 20
Empty the fuel filters into clear glass jars. Look for clarity, lack of suspended contaminants,or water at the bottom, It should not smell like varnish. It should have a strong gasoline odor. Verify that the plug wires are on correctly and the base timing is correct. If you have had wet weather recently, pull the caps and make sure they are dry. Lastly, you may need to rebuild or replace the carburetors. Jim <STAN_MUTE@YAHOO.COM> wrote in message Jim
May 20
From your description, the power loss and backfire is a lean-out JR
May 20
   

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