GX 390 will not start

[lkjhg]

I've powered my bcs605 with a recoil starting gx390 engine since 2012. I rototill, mow lawns, mow hay, push dirt, throw snow, pull wagons, and skid hay. It worked great until AUG 2020. I checked fuel and spark and I had both. I checked all the ignition wiring and found no issues. I checked the for low oil; no issues. Compression was about 80 psi but engine has compression release. I reset the valves which made the engine easier to spin but the engine would not start. Finally I changed the sparkplug and it started. I deduced it must have been the sparkplug. The gx 390 ran well until JAN 2021 when the temperature was 0 degrees F. I had spark, I had fuel, I used starting fluid. It would not start. The JAN weather warmed and surprise; it started. I deduced that I was not getting enough flywheel speed to get adequate spark. As in AUG, I could see the spark on the grounded sparkplug and on my spark detection tool but perhaps the spark was not adequate. While the engine was hot, I drained the 15w-40 and replaced it with 5w30. The engine ran great! Last week with 70F temperatures the tractor started on the first pull. It ran for 5 minutes. I engaged the mower deck and the engine stalled. Engine will not start. I have fuel; I have spark; I have injected starting fluid into the cylinder but engine will not start. I use ethanol-free fuel exclusively.

Now I am concentrating on the spark plug wire and the coil thinking that the spark is not strong enough.

Am I on the correct track?

 

[LittleBill21]

you can generally test the coils, to see a resistance measurement. but if you try to start it in the dark with a spark test you should easily see a blue arch. if not its shot, shorted or out of alignment.

 

[Roadworthy]

I have heard of corrosion on the magnet on the flywheel weakening or eliminating spark.

 

[RobertnVirginia]

I've powered my bcs605 with a recoil starting gx390 engine since 2012. I rototill, mow lawns, mow hay, push dirt, throw snow, pull wagons, and skid hay. It worked great until AUG 2020. I checked fuel and spark and I had both. I checked all the ignition wiring and found no issues. I checked the for low oil; no issues. Compression was about 80 psi but engine has compression release. I reset the valves which made the engine easier to spin but the engine would not start. Finally I changed the sparkplug and it started. I deduced it must have been the sparkplug. The gx 390 ran well until JAN 2021 when the temperature was 0 degrees F. I had spark, I had fuel, I used starting fluid. It would not start. The JAN weather warmed and surprise; it started. I deduced that I was not getting enough flywheel speed to get adequate spark. As in AUG, I could see the spark on the grounded sparkplug and on my spark detection tool but perhaps the spark was not adequate. While the engine was hot, I drained the 15w-40 and replaced it with 5w30. The engine ran great! Last week with 70F temperatures the tractor started on the first pull. It ran for 5 minutes. I engaged the mower deck and the engine stalled. Engine will not start. I have fuel; I have spark; I have injected starting fluid into the cylinder but engine will not start. I use ethanol-free fuel exclusively.

Now I am concentrating on the spark plug wire and the coil thinking that the spark is not strong enough.

Am I on the correct track?

I had a similar intermittent problem with a Honda 2 cylinder engine on a zero turn mower. It turned out to be that the inner coil spring wire conductor to one of the spark plug boots had gotten pushed back and was not delivering the full strength spark to that spark plug. If that is your problem, just pull the spring wire conductor back to its required position with needle nose pliers.