2002 Mercury 90 4-stroke Will Not Run

JDusza

Ensign
Joined
Apr 21, 2009
Messages
973
Hi. Hope all is well with you.
I am working on a 2002, 90 hp, 4-stroke, in-line-4 that has been sitting for a while. Here's where I am:
Compression: top-to-bottom: 180, 140, 140, 125. Yes. I know. Wouldn't it still run albeit never again at 90 hp ...?
Spark: jumps 1/4 inch air gap. Spark plugs fire even though they are NGK. lol.
Valve timing: alignment marks in spec. Compression up so valves seem to be closed.
Ignition timing: appears to be in spec at about 7 ATDC, signals clean, no cross-talk. 1 and 4 fire together and 2 and 3 fire together. Plug wires are routed from coils top to bottom as 1, 4, 2, 3.
A note on timing: the flywheel has been played with. The ring gear with the timing mark is not in proper alignment with the flywheel function nor true TDC. Seems to be about 60-degrees out which makes sense with six screw holes.
That said, it will not fire up. Add premix directly into cylinder and it will fire up. Add fuel into intake manifold directly after carburetors and it will fire up.
Went through all 4 carburetors. Still nothing. Opened idle mixture screws 4 turns out. Still no fuel. Only fires when fuel is added manually.
Carburetor questions:
Am I to adjust the floats to pull in more fuel?
What are the little black plugs for at the bottom of the carburetor in the bowl? Is this path supposed to be blocked or open or fluttering open/closed?
Should the carburetor primer starters actuate with 12 volts applied on the bench? I get no reaction. I have 4 of them and none of them react to 12 volts. Isn't it a solenoid that makes a pump? What do they do?
Why no fuel to cylinders?
Thank you,
J
 

JDusza

Ensign
Joined
Apr 21, 2009
Messages
973
Fuses okay.
Pretty much convinced there's not enough vacuum draw through the carburetor throats. If I completely block the carburetor throats, I will get fuel coming out the front of the carburetors resulting in a flooded engine that will start and run for a bit.
If the source of the vacuum is the cylinder, then if I have poor compression don't I have poor vacuum? Gonna have to check spec compression number...is that 180 legit?
Any idea what intake vacuum should be? Maybe I can measure at the intake manifold ports...
J
 

JDusza

Ensign
Joined
Apr 21, 2009
Messages
973
Got it running and found a throttle position where it will stay running. It pumps water well so I can keep it running in the driveway and to try to get some fuel through it.
The draw from the bottom carburetor (weakest cylinder compression) is by far the most. By comparison, the top 3 carburetors are not pulling anything.
I'm going to try and run it today and get vacuum numbers from the manifold ports.
J
 
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