2003 Tracker/Mercury 40hp 2stroke 2 cyl will not operate at full throttle when warm

[bernptl49]

Hi Guys,

First post here.

As above I have a 2003 Tracker/Mercury 40 Hp 2 Stroke 2Cyl single carb. It is mounted on a 2003 24' pontoon usually with 3 kids 2 adults on board

The boat starts fine cold, Choke-key-vroom...

Always idles fine....

Once under power I can get the boat up to 4500-4900 RPM (7-8.5MPH) and once I surpass 5000 rpm the boat will (as I can best describe) surge or starve its self. It nearly starves itself out. Its not cavitation. I've rebuilt the carb, all fuel lines and recently replaced the coils. I am stumped. I'm fairly mechanically inclined but absolutely stumped.

When the motor is cold it wont starve itself but once it warms up its game over. This is the original motor/prop/boat combo. Nothing has been changed.

I know the boat is underpowered and slow but the difference between 8 and 14 mph is huge when you're on the water.

Thanks in advance and any help at all would be appreciated.

-Cody

 

[DeepCMark58A]

I am having the same problem with an older mercury, have you checked the filter in the gas tank? I am plumbing in a gauge after the fuel pump to see what the fuel pressure is at full throttle, I will let you know what I find it might help you find your problem

 

[DeepCMark58A]

Have you rebuilt the fuel pump?

 

[bernptl49]

Have you rebuilt the fuel pump?

Yes sir.

 

[DeepCMark58A]

Well my problem was a bit different than yours my problem was at full throttle the motor would bog down after 30 seconds at full throttle, the motor would recover if I backed off the throttle. I got rid of the problem by going direct from the gas tank to the fuel pump. I should say I cured the symptom but did not solve the problem.

 

[bernptl49]

Well my problem was a bit different than yours my problem was at full throttle the motor would bog down after 30 seconds at full throttle, the motor would recover if I backed off the throttle. I got rid of the problem by going direct from the gas tank to the fuel pump. I should say I cured the symptom but did not solve the problem.

What was between the tank and the pump that you bypassed?

 

[ondarvr]

Squeeze the primer bulb when it's acting up, if this helps you'll know it's a fuel delivery issue, which is either an air leak or a fuel pump.

 

[DeepCMark58A]

What was between the tank and the pump that you bypassed?

The motor connection to the fuel line and all the fitting and restrictions.

 

[bernptl49]

Squeeze the primer bulb when it's acting up, if this helps you'll know it's a fuel delivery issue, which is either an air leak or a fuel pump.

No luck with that. I'm thinking it may be a bad ground somewhere or a spark issue. It's getting old only being able to do 9mph.

 

[ondarvr]

Check for spark when it's acting up.