this is list of parts i've changed . what next.

90hp mercury 4-stroke.

This motor goes dead usually at WOT. It idles good. And seems to run good early in the day . It goes dead more often when weather warms. 85+ . Sometimes when it goes dead the primer bulb will be flat, but not everytime. I've changed the primer bulb twice, the hoses, the anti-syphon valve. I have also unhooked the motor from the boats gas tank, and hooked it up to a new tank. No change. My mechanic replaced a fuel pump. I think it's called the external fuel pump. No change.

My mechanic said there was another fuel pump . Could that be the bad one? Should I try another mechanic? Is there anything else I can do? Thanks

Re: this is list of parts i've changed . what next.

Is this an EFI (fuel injection) motor?

Re: this is list of parts i've changed . what next.

First off, we need the correct model and seriall # of your motor to look it up.

Second, it sounds as tho you have two separate issues;

One, a fuel restriction BEFORE the primer bulb,

the Second as yet to be determined, temperature related. This is why we need to see exactly what model you have.

The fuel issue may be crud in the fuel tank, restricting fuel flow in the dip tube, also ensure that the fuel tank vent is not restricted, causing the fuel pump to pull a vacuum on the tank, thus collapsing the primer bulb..

As for WOT dying at warmer temps, you need to immediately perform a spark test to determine if it is an ignition issue or fuel issue.

Repost when you have more information and we will further advise then.