5.0 backfires - problem solved!

[SC74]

I piddled on this some yesterday and figured out that the trouble starts as soon as the temp hits 150* - not even hot, warm at best. It has plenty of power before it reaches 150* (which isn't long) - I dug a hole in the yard when I pulled up the the mulch pile - no hesitation and no backfiring. As soon as it hits 150* it starts puttering - can't even touch the throttle without it backfiring and most likely cutting off. I tried to limp it back to the concrete going 10-15 ft at a time and it stalling.

After getting it back on the concrete I let it sit and would key-on every once in a while to see the temp reading. I tried several times while it was 150* or just over and it just stuttered and backfired. I let it get down to about 130* and it ran perfect until the temp got back to 150.

I'm thinking it has to be a sensor from when it changes from "cold choke" mode to normal operating temperature mode.