loss of power over 3500 RPMS FYI

[chs marine service]

i have come across this issue about 4 times this summer and wanted to post it here in case others are experiencing this issue.

boats would run great at idle and under load but when you climb over 3500 the engine would bogg down and stall. and may keep running if you pull back on the throttle but may also die.
i would run the engine with an external fuel tank and it would operate properly.
i have in all these cases, replaced the anti siphon valve and supply line hose.. this has solved the issue.

 

[Scott Danforth]

did you check fuel pressure thru the RPM range under load? curious to see what it drops off to

 

[kenny nunez]

Another trouble area is the fine mesh screen inside the suction tube. That screen causes a lot of problems.

 

[alldodge]

Don't think it's a chain saw, but what motor you talking about?

 

[tank1949]

Check blocked air vent on side of boat. Mud dobbers and corrosion love those small screens. I pulled screen out many years ago that had green crap on it. I had a similar problem as you described.

 

[chs marine service]

Don't think it's a chain saw, but what motor you talking about?

one was a 5.7, one was a 4.3, one was a 3.0, one was a 5.0
its not the engine that has the issue, its the delivery system,

 

[chs marine service]

Check blocked air vent on side of boat. Mud dobbers and corrosion love those small screens. I pulled screen out many years ago that had green crap on it. I had a similar problem as you described.

yes, before going to the external tank, i always run the boat with the gas cap off to test,

 

[chs marine service]

did you check fuel pressure thru the RPM range under load? curious to see what it drops off to

no, i did not

 

[jimmbo]

Easy to diagnose Carb System(s), or next to impossible Fuel Injection?

 

[kenny nunez]

Have you ever tried using a 6 gallon outboard tank? That will narrow down the problem to either point to the tank or the engine’s fuel system.

 

[chs marine service]

Have you ever tried using a 6 gallon outboard tank? That will narrow down the problem to either point to the tank or the engine’s fuel system.

yes as stated above : "i would run the engine with an external fuel tank and it would operate properly."