Engine power loss

[MajorPainage]

Just feeling out some suggestions. We have only used the boat 1-2 time a summer the past 6-8 yrs because summers have been very busy. Boat has a 90hp Johnson motor and boat has an under the floor fuel tank. The issue is that the boat starts and runs fine, can take off up the river and it has plenty of power. After 10-15 minutes it drops in power. Speed drops about 5-10 km/h. if we push and hold the key in to choke it, it continues back to normal power. so it clearly seems like a fuel starvation issue. We've had a few suggestions being that the fuel tank vent may be plugged and restricting the flow, and the other being a carburetor issue maybe being dirty from lack of use. once we get to the fishing hole and after a couple hours, it starts fine, runs at full power, and again after 10-15 mins we see power loss again. the plugged vent sounds possible but i'm not sure where to look for the vents or what they even look like. any suggestions where to look and what to look for?

 

[racerone]

Run fuel out of the carburetors when you are done boating.-----Empty carburetors stay clean.

 

[tphoyt]

Vents can very in location but the most commonly are on the side of the hull just below the run rail.
Usually round and most often chrome in color.
Bugs like to make nest in them.

 

[saltchuckmatt]

Most likely it your pickup screen in your tank....not your vent.

Put a portable tank in and test.

If that does it, install a spin on fuel filter and remove the screen from the pickup tube.

Do you run ethanol fuel in it? Do you fill your tank during the off season. How your gas cap....I must have changed hundreds.

 

[MajorPainage]

Thanks for the replies. I found the vents and they weren't plugged. Funny because mud wasps always plugged the rear of the engine cooling discharge. My dad ventured into cleaning the carburetor and found a little bit of gunk. In the process of finishing the repair and testing it out. In the fall fuel stabilizer is added and the tank topped off. Always high test fuel. For the screen in the tank, we had a couple years ago taken it all apart and pumped out the fuel tank to remove anything that shouldn't be there and remove possibly older gas. We will see how it goes on the next test run.

 

[cyclops222]

Why would you remove the fine screen in the tank pickup tube ?

 

[airshot]

Use the octane fuel your motor is rated for. Using high test fuel in a motor rated for 87 is a waste of money and can cause a loss of power ! Clean out your fuel tank, get rid if all old fuel. Be sure you have a fuel filter in place and change it every year. Use fuel additives for storage. Only getting used a couple times a year is not good for the fuel system !!

 

[saltchuckmatt]

Why would you remove the fine screen in the tank pickup tube ?

Read post 4....

 

[cyclops222]

A lot of what if's. I have had tanks sent out to be steam cleaned. They had large balls of slime and varnish break loose and stop gasoline flow.
The fine screens would allow roll off of the screen mesh and allow limping back to boat ramp. After many limp homes. We drained & used a camera in the tank.. It was a good sized slime ball.