Sears Craftsman II stopped firing on one cylinder

[vg066833]

This tractor has an 18hp Kohler twin cylinder engine model MV18S. Suddenly engine acted like it was running out of fuel and died. Checked fuel tank, gas present but topped off tank anyway. When it finally started, was with choke partially in and would not run without choke partially closed. Engine smoked and was not running smoothly. Found that it was only firing on one cylinder, thought a plug had fouled out installed new plugs still no difference. Oil smelled like gasoline and was above max line on dip stick. Changed oil and filter, still no difference. Removed carb and cleaned, made sure all orifices were clean and clear. Re-installed carb still no difference. I have a new coil and plan to install it tomorrow but I suspect it will not make a difference. Took the head off on side that was not firing, cylinder looked OK, valves looked ok and was operating when I cranked the engine. Any ideas?

 

[mini14]

Crankcase filled with oil would usually mean a stuck open float.

 

[vg066833]

Float not stuck, removed carb, as I stated, checked that it did indeed float in gas, no fluid inside it and needle valve and valve seat in good condition, clean and clear orifices. Any other ideas?

 

[Maxify55]

OHV?
Your gap set/valve lash could be out of spec.
Check for your Mfg specs regarding such & re-gap “.
Been having trouble starting it?
There’s your problem

 

[rangerfredbob]

I think that engine has a fuel pump which has a vacuum port going to the intake manifold, the diaphragm probably failed and would do what you are talking about.

 

[LS Tractor Owner]

^^^^^ yep, had the fuel pump fail (diaphragm) and it dumped fuel back into the crankcase through the hose leading into the cylinder head valve cover. Replaced the fuel pump and no problem. (kohler 26hp)

 

[tomplum]

Yes, very likely the fuel pump. Magnums have a mechanical fuel pump as a note.

 

[vg066833]

No, there is no vac line, this pump has a mechanical actuator that extends into the engine and rides on a lobe. Checked the output of the pump when I had the float out by cranking engine and fuel squirted out with every rotation of the engine. Will check pump diaphragm for cracking.

 

[vg066833]

This fuel pump has hose from tank and hose going to fuel bowl on carburator.

 

[vg066833]

No OHV, removed head to look at valve and top of cylinder, as I stated. This engine is an opposing twin cylinder. Cylinders ard in a 9 and 3 o'clock configuration.