Carb Issues At Small Elevation Change?

[dpapa1911]

Hi All - have a Merc 3.0. Boat lives at 700ft elevation. Came up for a long weekend to Northern Wisconsin. Brought the boat for the first time. Immediately noticed hesitation when trying to throttle up. At some points the engine would die while trying to accelerate and I’d have to restart. Eventually would be able to push past the stumble spot and get up to speed. Lake is at 1,700ft elevation. Could 1K elevation change really cause enough of an issue with fuel/air mixture to cause this? Is there a simple adjustment most make in these cases that I should be aware of? Thanks.

 

[Scott06]

Hi All - have a Merc 3.0. Boat lives at 700ft elevation. Came up for a long weekend to Northern Wisconsin. Brought the boat for the first time. Immediately noticed hesitation when trying to throttle up. At some points the engine would die while trying to accelerate and I’d have to restart. Eventually would be able to push past the stumble spot and get up to speed. Lake is at 1,700ft elevation. Could 1K elevation change really cause enough of an issue with fuel/air mixture to cause this? Is there a simple adjustment most make in these cases that I should be aware of? Thanks.

Normally that shouldn’t make a difference With such a minimal altitude diff. Would suspect you have a fuel delivery to carb or carb rebuild issue.

if you slowly advance the throttle does the problem occur or only if yiu stab the gas.
what is the maintenace history of boat? Would start with fuel filter and see what contents show you.

attached is an excerpt out of a mercarb manual shows jetting recommended at altitude. Below 5 k ft( yes 500 is a typo…) same jetting, so you should have no issue with 700-1700 ft. Likely you will see same issue back at 700 ft

 

[dpapa1911]

Normally that shouldn’t make a difference With such a minimal altitude diff. Would suspect you have a fuel delivery to carb or carb rebuild issue.

if you slowly advance the throttle does the problem occur or only if yiu stab the gas.
what is the maintenace history of boat? Would start with fuel filter and see what contents show you.

attached is an excerpt out of a mercarb manual shows jetting recommended at altitude. Below 5 k ft( yes 500 is a typo…) same jetting, so you should have no issue with 700-1700 ft. Likely you will see same issue back at 700 ft

Thanks. Throttle issue occurred when slowly accelerating. Would have to move throttle up and down and sometimes punch it hard and fast to get through the stumble.

Changed the fuel filter 3 years ago when I got the boat so due for a change. Will swap with new and see how it goes.

 

[Bondo]

Thanks. Throttle issue occurred when slowly accelerating. Would have to move throttle up and down and sometimes punch it hard and fast to get through the stumble.

Changed the fuel filter 3 years ago when I got the boat so due for a change. Will swap with new and see how it goes.

Ayuh,..... Welcome Aboard,.... That should be in the Annual Maintenance,...
Boats, like anything else suffer, 'n fail, when not maintained,....

 

[Scott06]

Thanks. Throttle issue occurred when slowly accelerating. Would have to move throttle up and down and sometimes punch it hard and fast to get through the stumble.

Changed the fuel filter 3 years ago when I got the boat so due for a change. Will swap with new and see how it goes.

Sounds like some of the passages in the carb are plugged probably the transition circuit, if you mash the throttle and that helps seems like accelerator pump is working.

As Bondo said fuel filter is a good annual maintenance item - check what comes out of it. With mositure and sitting typical for boats to get fuel contamination.

 

[dpapa1911]

So brought the boat back to normal elevation. Same issue. Changed out the fuel filter. Still same issue. Checked fuel vent line - it’s clear.

Seems to run ok when started then as I accelerate starts to stumble and die. Ordered a rebuilt carb to see if that remedies. After that don’t know what’s else to try.