2000 Mercury 150 XR6 problems when outdoor temperature is hot

My motor starts and runs fine when temps are below about 80 degrees. When outside temps are hotter, I have problems. Engine may be at an idle and it will die. Continue cranking and it will not start until throttle hold is wide open. Finally starts but runs rough then will clear up. Accelerating it will run okay but then back to dieing and hart to start. Only happens at hotter outdoor temperatures. Cool weather it performs great. I've had it checked out several times and the mechanic can't figure out what the cause is. Any suggestions? Thanks.

Re: 2000 Mercury 150 XR6 problems when outdoor temperature is hot

You can assume it's running a bit rich. Warmer air temp makes that problem worse.
If it were mine, I'd:
Check compression, just to be sure I'm not chasing my tail.
Put in 2 carb gasket kits. 5-6 bucks apiece, and gives me a chance to examine the jets to be sure they're stock, or off stock the right amount for your altitude. Also I'd examine the needle valves under high magnification. Set the floats right on to just a hair high. (in the measurement)

Put in a fuel pump kit. A pinhole leak in the diaphragm can act like this.

While the carbs are off, check the bleed lines for condition, routing, and valve operation.

Do the linkage and timing adjustment procedure.

If it still acts the same, put in .002" bigger idle jets.

Gaskets and kits will run you about 30 bucks. It'll take a day of yer time to get to intimately know your motor.

I suggest you acquire a Mercury Service Manual before you start the project.

hope it helps
John