What you think, 40 HP YAM F40TLRA model

[roscopico]

Engine does not want to run on idle.
Will start only on the high idle remote.
Will push the boat on low speed, when I push for high speed it cuts off.

my conclusion: fuel/vacuum/carbs issues here.

1- If its running on high idle, then carb is clean right.,there is no restriction. and its getting gas.

2- It ran in the water pushing boat on low speed. so we are getting gas, fuel pump is pumping.( low-speed for me mean, only can push the trottle half-way)

LOST:

[Hotrod]

Bad seals.  A rebuild is in order

[roscopico]

You mean the gasket are broken, and there is lost in the vaccum, probably in the high speed top carb.

[roscopico]

Come on guys, need more response here

[Maritime Matt]

Carbes or fuel injected? Sounds like clogged jets to me. I've lost tract how many carbs and fuel pumps I've done. That is a 4 stroke, correct?

[wb]

Outboards can be funny sometimes and throw you for a loop.

My buddy had a Johnson 90 same prob you describe he redid the carbs a couple times ran good only if you choked it

turned out his lower unit was seizing ever so slightly-- nothing really noticeable other than it wouldnt run past 1500r's

first time I ever saw that--all the smart money was on carburetion problems

doubtful it's your LU, just an example that you may need to think out of the box here...

[Maritime Matt]

Wow, first time I ever heard of that one but with boats and salt water anything is possible.
I'll keep that one in my head. Matt.

[Hotrod]

You mean the gasket are broken, and there is lost in the vaccum, probably in the high speed top carb.

Yea.. ros..  either way  a carb rebuild should fix it
I had the same problem on another boat of mine.  like Capt Matt said.  clogged jets..  clogged something restricting fuel.

[Reckless]

 Could be electrical also. Bad coil condenser breaks down under load. Timing not advancing etc.

[roscopico]

Thanks guys, I will start with the high speed carb, and see what happens.