Runs good at idle but as soon as you throttle up engine dies.

[RebTech]

I completely rebuilt my boat and this is our first day at the lake. I have a 3.0 XL alpha one, The Motor runs when at idle but as soon as to try to move it into gear with a bit of throttle it stalls out, same goes if it's not in gear and just revving the engine. In other words, low idle is good and full throttle (but will kill itself if left to long at high throttle. everything was marked and replaced exactly the way it was during the build.
Only thing I can think of is that I added a 3/4 can of seafoam to a fresh tank of gas of 80 liters after the rebuild.
can anyone make some recommendations to help us out?

 

[jimmbo]

Dirt/varnish/gum in the carbs Off idle transfer slots and/or Accelerator Pump is likely the cause

 

[RebTech]

Spent the day at the lake messing with the carb. Took the fuel filter out and was completely plugged. Motor runs good at WOT but still dies when coming down from full. We shot some seafoam directly into the carb and used some carb cleaner.
We are now boating for the rest of the week here. Will rebuild the carb in the fall.

 

[jimmbo]

Get some Mercury Power Tune, or BRP engine Cleaner, Spray some of that into the carb bowl when the engine is running, it might dissolve the vanish and gum. I have used it in a pinch in a non-recommended procedure , putting a can of it into a portable tank with a few gallons of gas, . It is a much better cleaner than SeaFoam, which is mostly a very thin oil. Some people swear by the stuff, I swear at it

 

[Scott Danforth]

there is no mechanic in a can.

pull the carb apart. soak it. chase all the passages, especially the idle circuit and accelerator circuits

then put it back together with new gaskets.