Engine running rough

[rv4dude17]

I haven’t flown the rv in about 3 months, but today, I
Went to fly. However, after starting, the engine ran rough.
I shut it down and took the cowl off to try to find the
Problem. Cylinders 2,3 and 4 were very hot, but cylinder #1
Was not. I immediately thought stuck valve , so I removed
The #1 valve cover and all 4 top plugs. When turning the
Prop by hand, the valves seem to move normally. I put the
Valve cover and top spark plugs back on and Turned the prop
Though 4 blades. All compression strokes are about the same.
I’m not sure what else to check. Any help??
Carburetor and slick mags.

 

[blaplante]

Maybe... bottom plug is oil soaked and top plug not firing for some reason? Hence it doesn't clear the bottom plug.

 

[D-Dubya]

Do you have an engine monitor with CHT/EGT for each cylinder? If you do, what were those showing when you did a mag drop test?

 

[[email protected]]

And you missed the opportunity to see what the bottom plug looked like.
Take a look and check the oil soak and resistance on the plug. And borescope if you have one.
It's a real quick operation to answer a lot of questions.
My luck varies Fixit

 

[rv4dude17]

David. I didn’t do a msg test but cyl 1 cht and egt were very low.

 

[rv4dude17]

I’ll check the bottom plug.

 

[lr172]

I’ll check the bottom plug.

In order for a cyl to go cold, BOTH plugs must stop firing, so ignition seems a bit improbable, though still possible (cyl will make 90% of it's power with just one plug). carbs rarely create individual cyl fuel delivery problems. I would consider a wobble test on the #1 exh valve, as compression seems the most likely culprit.