Mercury 90hp 4 Stroke Stalling

chavis07

Cadet
Joined
Jun 25, 2015
Messages
8
I recently purchased a 2005 mercury 4 Stroke (carb). I have replaced the fuel line completely (from tank to motor) and added a water/fuel separator. Running it on the hose, it runs fine (idle & will take throttle). When i put it in the lake (water), it acts as if it?s starving for fuel. From 1000 rpm's to 2000 rpm's it bogs and acts as if it won't take the throttle. I can nurse it past this point and it runs fine for a few seconds then acts again as if its starving for fuel. I can pump the primer ball and it runs fine (as long as i pump the primer ball every so often. Please help. I have ran it straight from the tank (bypassing the water/fuel separator) and it does the same thing. Carbs were rebuilt 3 weeks ago by Marina and i have been running Fuel treatment. Pickup in tank has been replaced along with cleaning tank and fresh fuel.
 
Last edited:

Dekker500

Seaman
Joined
Jun 25, 2015
Messages
58
From the way you describe being able to keep it going by manually pumping the bulb, it sounds like a fuel pump issue - possibly just the diaphragm.

Another simpler possibility is an air leak somewhere in the fuel line. Check for "wet" spots on the line as you pump gently while connected to tank but not connected to engine - not the best test, but simple starting point.
 

chavis07

Cadet
Joined
Jun 25, 2015
Messages
8
Thanks Dekker500. I've looked for leaks everywhere before and after changing the hoses. Please take a look at my next post as it concerns me. Thanks again.
 

chavis07

Cadet
Joined
Jun 25, 2015
Messages
8
Update.. Went out this morning and checked all lines again while pumping the bulb. Found nothing leak or pulling in air. Did find this interesting tho. I pulled the hose from the top of fuel pump and blew air (by mouth) back towards the carbs and heard air near the bottom carb. Put suction on it and couldn't get air to move back towards fuel pump. Should this be happening or does it seem weird?.Tried to upload image but its not working.
 
Last edited:

chavis07

Cadet
Joined
Jun 25, 2015
Messages
8
Went out yesterday and primed the bubble. Got hard and is still hard this morning.
 

chavis07

Cadet
Joined
Jun 25, 2015
Messages
8
I've checked fuel lines to include everything from the tank to the motor. I'm thinking fuel pump also. Just trying to trouble shoot before breaking into the fuel pump. This motor only have 115 hours on it. Thanks.
 

chavis07

Cadet
Joined
Jun 25, 2015
Messages
8
Installed new fuel pump which worked well.

Idle is still awesome.

From the hole shot to top end is perfect.

Still tends to struggle a little from 1500 rpm's thru about 2500 rpm's while cruising along. Seems to either load up on fuel or starving for fuel (haven't figured that one out yet). It will sometimes stall (if left in that position) unless throttle is advanced. I'm thinking another reset of carbs.

Any ideas.

Happy for not having to squeeze the primer bulb anymore. Looks as if its coming together. Thanks guys.
 
Top