Logo

1980 Mercury 70hp 3cyl carb problem

hunter2664

New member
Hello. I'm new to this bo

Hello. I'm new to this board I would like to introduce myself. My name is Jim OBoyle. I'm new to boating but have been an ASE certified automotive technician for 13 years. So I would like to think I have pretty good understanding of how motors work. However I am stumped by a problem I'm having with my Mercury outboard. The motor is a 1980 70 hp 3 cylinder. I purchased the motor not running.I rebuilt the powerhead due to the number one piston failing (melted piston). At the time of the rebuild I also rebuilt both carbs and replaced the reeds because they were out of spec. The water pump is new. The problem is that I decided to start the motor at home before I took it to the lake. When I started it the motor idled extremely high so I adjusted the idle down first then I discovered the bottom carb (2 Carb system)was leaking fuel from the inlet jet as well as from the center horn after a few seconds of running. I removed the carbs and reset the float levels as well as swapped the needles and seats. I still have the problem. It seems to get better somewhat if I turn in the idle screw (the manual recommends 1 1/2 turn initial setting) but I'm afraid that it might run lean. Any help on this problem would be greatly appreciated. Thank you in advance. Jim
 
THERE ARE HIGH SPEED NEEDLES

THERE ARE HIGH SPEED NEEDLES OR METERING JETS IN THE CARB. THAT CAN NOT BE ADJUSTED.THE METER JET ON THE CARB. ARE FOR LOW SPEED OR IDLE. I HAVE A FORCE120HP FACTORY LOW SPEED IS SET 3/4 TURN ON EACH CARB.I GET THE BEST RMP. WITH THIS ADJUSTMENT;BUT LIKE YOU I THINK IT COULD BE A LITTLE LEAN;SO I OPEN THEM TO 1 FULL TURN ON EACH; I AM SHURE YOU ADJUSTED THE LINKAGE TO LOWER IDLE. GOOD LUCK
 
" Yes, I did adjust the linkag

" Yes, I did adjust the linkage to lower the idle. The carb has a removeable jet to the left(looking at the carbs facing the bow) this is where the fuel is coming out of kind of spitting it out as well as from the horn area.
Thank you for the reply. "
 
"Hunter,

The jet where you


"Hunter,

The jet where you noticed fuel spitting out is the vent for the float bowl.

The float chamber is flooding, probably due to a problem with the float or the needle and seat.

Another possibility (very rare) is that the fuel pump is blown. This can cause crankcase pressure to go through the pump and directly into the carb inlet lines.

"
 
I rebuilt the fuel pump also d

I rebuilt the fuel pump also during rebuild. I replaced the needle and seats in both carbs also swapped the needles and seats between the carb. I just swapped the carbs top to bottom and I'm still having trouble with the same carb. I taken it apart three times now and can't find anything wrong. I tested the float it does float I'm stumped. I'm going to try and find another carb. If anyone can knows wher I might find a used one please let me know. Thanks for the help.
 
"Hunter,

Sometimes the spot


"Hunter,

Sometimes the spot on the float arm that contacts the needle valve becomes worn. I have seen very tiny, seemingly insignificant imperfections that caused the float to stick and therefore a flooding condition.

Just a guess, but it is the only thing I can think of.

When you squeeze the primer do you notice fuel leaking out of the same locations?

"
 
"Hunter,

Another thing that


"Hunter,

Another thing that came to mind after reviewing the parts diagram is that these engines were built with two different carbs WM-11 and WM-13.

They use different needle and seat assemblies. Is it possible that you used the wrong part when rebuilding the carbs?

"
 
Thank you for all the help. I

Thank you for all the help. I replaced the float today and the problem is fixed. Now I get to go break in the motor!!! Again Thank you all for the help!!
 
Back
Top