1990 Mercury 4 cyl 40 question

[69starcraft]

I'm working on a friends motor. It was pretty well boogered up by a "professional Marine Mechanic" who supposedly did a carb rebuild last year.

My immediate question is the front of the carbs...

Behind the oil tank the fronts of the carbs are wide open...there is no air filter, no breather box, no nothing... According to the diagram online I am staring right at the main fuel jet? There are also two plastic circles in the center of the carbs.

I've worked on car, tractors, boats (johnsons mostly ) and motorcycles.
I'm not familiar with this carbsetup, and I suspect there is a piece missing...

It's hard to start, only runs (somewhat) with choke in...carbs dripping fuel so I am tearing them down now. Other than NOT seeing new gaskets and seeing shoddy work the carbs are pretty clean. Obviously the professional marine mechanic doesn't know the difference between metric and standard, and that brass is delicate.

Any insight? I can't see the main fuel jet is wide open to the air like this

BTW compression and spark test were good Problem is definitely in the carbs somewhere

 

[achris]

Re: 1990 Mercury 4 cyl 40 question

Hi there,

There is no air filter or air box on these engines. I've posted up a parts breakdown of the carb. If that doesn't help, post up a photo of the area you've got problems with.

Chris.......

 

[69starcraft]

Re: 1990 Mercury 4 cyl 40 question

Well, I put it all back together, thanks for the info on the breather box, or lack of.

took it out on the lake for a quick and cold test drive.

She started and idles fine in spite of it being 30 degrees and not starting it for 3 days while it snowed for 2 of those days

Backed out of the ramps and turned it around and gave her throttle. At first she started to go fine and plane out....we got on plane and she started lurching. Reached back and check the fuel ball and its soft so I give it a few pumps and she picks back up again.

Then just as I think shes good she starts lurching again...again with the fuel ball and she picks back up...

However the third time pumping the fuel ball does nothing, and full throttle becomes about 1/2 throttle, and then about 1/3

head back to the ramp and slow it down and she idles fine

Then the overheat alarm starts off (steady tone), however she's peeing fine and doesn't feel too hot. She's oil injected, i prefer mix yourself, but I see give or take the appropriate amount of smoke. I know thats not a "real " test but she looks normal there...


Forget about full throttle, idle and a little extra is all i get now. No plane, and acting sluggish. However stops, starts and idles with a bump of the key, like a brand new motor.

So We Head back to the ramp and load her up.

So any advice from here....it's not my boat nor motor, but a good friend. I am a johnson man and much more comfortable with them

What I did so far is tear down both carbs and clean and re-install...figured maybe I might need to adjust lean/rich at fast RPm?? Idle and starting are great. When I got it I couldn't start it at all until I cleaned the carbs (which BTW were not filthy at all)


I did a compression test all 4 cylinders about 120 give or take but within range of each other

Plugs are fairly new (last year, with about 30 minutes total on them)

I noticed fitting (quick connect) for fuel line to motor was leaking if pumped too hard, thought maybe it was sucking air (my West bend did that) and solution is to replace with a straight fitting for now.

Any thoughts?

Thanks

 

[coolguy147]

Re: 1990 Mercury 4 cyl 40 question

i would replace the impeller and t stats.

did you clean the carbs and readjust the float properly?

check for spark?

i would service the fuel pump

replace fuel lines and filter. make sure there is no gunk in fuel tank pick up or tank.

open vent