99 40HP one cylinder lean other perfect.

[Bryrawski]

Currently rebuilding a 99 force 40 HP. Took apart head to clean cylinders after tapping out adapter plate bolts (of course they broke off durring gasket replacement process) any ways does anyone have an idea why one cylinders is running at good air/fuel mixture and other is lean as can be?
I could only assume I have a clog somwhere but don't know where to start trouble shooting since it's a single carb motor and run off of same fuel lines. "Freshly rebuilt carb"

 

[pnwboat]

Compression will affect cylinder mixture flow. The down stoke of the piston is used to pressurize the crankcase to force the air/fuel mixture into the by-pass ports (intake) of the cylinders. Also take a look at the reed valves too. Not sure if the reed valves are cylinder specific or if they are common to both cylinders though.

 

[Jiggz]

As mentioned, check and compare compression. Thereafter, the only other thing that could affect mixture flow are the reeds.

 

[jimmbo]

A leaking crankcase can cause a lean condition. Often the seals on the crankshaft wear allowing air to be sucked in and gas-oil to be blown out. Water ingestion can also steam clean a sparkplug making it look like the cylinder is lean. Did the old head gasket show any signs of water leakage?

 

[jerryjerry05]

What cyl??? More info?
Compression?
The cyl. port cover gaskets.
They can blow out in a second.
​You might have to silicone them in place.

Each cyl. has it's own reeds.

jimmbo might have something with the crank seal on the lower cyl.
​Also the ring seal on the crank could have broken?

 

[Bryrawski]

All head gasket was in good condition. I will check compression and reeds next.
As stated above water could have been a cause since whole reason of rebuild was because of leaking lower adapter plate gasket filling cull with water.

 

[Jiggz]

There you go. If water is leaking from the adapter plate it means there is water intrusion into the cylinder causing what might look like a lean fuel oil mix but is actually steam cleaning.