Generac generator using Champion vs Autolite spark plugs comparison

[staninlowerAL]

In January 2025 I was able to make the necessary repairs to resolve the uncontrollable overspeeding problem experienced with my Generac 990 17.5kw portable generator: https://farmallcub.com/community/th...enerac-990-portable-generator-17-5-kw.117768/ and I also done the annual service and tune up at that time. It's been running very well since that time up until recently when it had been running for about an hour, operating at high idle, alternately with load and no load and abruptly shut down. I restarted it but it did not want to run smoothly so I shut it down for the day. I've started and run it a few times without further problems since then but not for as long a period as before. I have also not experienced the shutdown again either. So this brings me to the question: The unit is about 20 years old and has probably less than 500 hours of run time. First step is to try a different plug from the Champion RC14YC that's called for in the specs sheet and currently in use. Thinking about trying Autolite 3926 which is supposed to be a compatible plug, any thoughts pro or con on this? Due to it's age I've considered that the coils may be aging out but don't want to go there just yet but that's one avenue that I've considered. Any thoughts, comments, suggestions welcomed. Stan
EDIT: As you can see, this is my emergency power supply so I want to make it as dependable as possible.

 

[MiCarl]

With symptoms like that the first thing I'd look for is a clogged vent in the fuel cap.

Fill the tank full and run it until it quits. Remove the fuel cap, then put it back on. Start it back up and see how it runs. If it runs for awhile the second time then quits clean or replace the fuel cap.

 

[staninlowerAL]

With symptoms like that the first thing I'd look for is a clogged vent in the fuel cap.

Fill the tank full and run it until it quits. Remove the fuel cap, then put it back on. Start it back up and see how it runs. If it runs for awhile the second time then quits clean or replace the fuel cap.

Thanks, I'll check the vent, I had not yet considered that possibility. It's the same type fuel cap on Cub Cadet mowers, I'm pretty sure they will interchange. Stan

 

[SONNY]

sounds like gas related ---fighting a Honda motor on my truck unit doing the same thing. Had to unbolt the thing from the floor and one of the 4 bolts was not possible to get wrench on since they put side boxes on AFTER they put gen on. anyway I have to take the gen off to reach the carb side and I think its junk in the carb causing the shutdowns and rough runin. ---- mine finally died out and wont run much even with the choke on. gotta be carb.

 

[Don McCombs]

Ahhh… those nasty, naughty carbs. Without clean and adequate fuel and air, the perfect carb will never function properly. You might be able to troubleshoot those things first without removing the generator.