Engine quitting - why?

[Robertc]

I now have two engines that will quit dead cold - like a plug being blown after 3-6 laps.  Very consistent.
I changed plugs, fuel, fuel line, NVA.  Nothing changes.  One engine is an old FP 40 and the other a LA 46.
The engines cut is very abrupt.  There is no change in engine speed.  One week, everything works perfect,
next week, this starts.  One engine started this about 7 weeks ago and the other this weekend.  Other engines
work fine.
Ideas?

[Tim Wescott]

Stopped dead & stayed dead?  Or stopped dead and then restarted after cool-down?

Same plane?

What's the old & the new fuel?

Have you insulted anyone with the Evil Eye lately?

[Robertc]

Restarted no problem.  !0% Sig and the other was borrowed from a friend.  Don't remember exactly what it was. 
Different planes.  One is a profile and the other built up.  Evil eye, well, maybe??

[phil c]

I'd suspect the plug.  When plugs are run rich and then the plane quits by going lean, depending on the fuel and how llong/how lean, it can cause deposits on the coil. Adding Armorall or similar stuff can make it worse.  It may start to run ragged first.  Eventually it won't stay running when  the starter is removed removed.

Another contributor can be moisture in the fuel.  On a hot, humid day I've seen a half full gallon jug go from great to barely runnable in a couple hours because the guy left the lid off.

[Steve Fitton]

what plug you running?

[Steve Helmick]

Same fuel filter? Same muffler? Some have reported such strangeness from coked-up mufflers or glazed over filter screens that look clean, but don't flow enough/long enough. I hope I'd just run a whole tankful on the ground and see if the same thing happens, tho it wouldn't pinpoint anything in particular. Could indicate a flake of solder or something inside the fuel tank, perhaps? I'd take note of the run time. Steve