Kent W., I had the sticking valve issue on a 129 that I traded for from a neighbor/bud. His dad had just rebuilt the engine, and it runs strong enough. But, then it was going dead after getting 30-45min of operation to get good and hot. So, he replaced the head gasket a few times, thinking it was that (I don't know if he resurfaced the head well or not). When I traded him out of it, I had the same heat-up and shut-down behavior with it that my bud was having (similar to what you describe). Hotter the summer day, the more (and quicker) it did it. When it would quit, it would go dead abruptly, and would spin down freely, as tho' it had no compression (which made me think that it might be the sticking valve issue, from reading archive forum stuff on this site). I changed the oil (where they'd been running multi-grade), and put straight 30wt in it, and I ran Marvell Mystery oil in the fuel (at about 2x the recommended mixture for putting it in gas) for a few tank-fulls of gas (to attempt to clean deposits around the valves). I don't know if the Marvell thing is voodoo or real, but I just tried it and things seemed better. I can't say that it'll never go dead abruptly again, or even that I correctly identified the problem and resolved it... but... it seems to have "fixed" my similarly-acting go-dead issue, and I mowed quite a few hot days after that without the go-deads. I did fish around the wiring about the condenser and points a bit (as others pointed out), where I needed to replace that wiring (and still do), so there could have been a red-herring on the sticky valve supposition in my case, and it could have been either wiring and/or sticky valves. Food for thought.
Todd, that same neighbor of mine had a '88 Chevy 4wd pickup with the exact same issue on the fuel pump, and they had to go thru three new ones to get a good one. The more he asked around, the more folks that told him the same story. Nothing against the brand, and his truck was a great one (had over 250kmi on it, when he sold it, and it looked, ran, and rode like a 50kmi truck), but that appears to be a common issue with the pumps.
