Bad or incorrect fuel? Water in fuel?

Same spark plug in the 680, no change in condition or symptoms.

Nope, I drained the gas tank the first time I pulled the carb just to eliminate that possibility. There wasn't much fuel in there.

This is what I'm thinking/hoping. I read up last night on valve adjustments and engine disassembly. If I get lucky I won't have to go that far.
I have the feeler gauges I need, but I also got a honey-do list for my wife's business today. She's got a big event this weekend, so the 1450 will have to sit till next week.

Will update again when I figure something out or fail...

Ok. If i read your post correctly, you said that it was running but bogged down and died and not will not restart. Im going to go for a blown head gasket or the head has a build up of carbon. I had the same problem with one of my QLs.

Id try pulling head, cleaning it and double checking head gasket.

Hope you fix your problem.

John

I'm sticking with valve issue...

Wanna bet? :biggrin2:

Torque back the head and adjust the valves clearance first as indicate in Kohler service manual (Section3 page5).If this not solve your problem collect Jonathan, I agree with his statement but it's his bet :biggrin2:

These "remote diagnostic" exercises are always interesting. So I've been following the discussion. I usually side with Jonathan on these, based on his extensive experience (and he's usually correct) but I'm curious what about the symptoms points to valves?

The tractor ran, then something changed and now it won't run. It backfires, so that sounds like timing or valve problem. Is it "backfiring" out the carb or is it "backfiring" out the muffler?

How could the valves go out of adjustment all of a sudden? so much so that now it won't start.

Blown head gasket shouldn't cause it to not start (usually) and doesn't account for the backfiring.

To me, it's unlikely the valves went out of adjustment. All of a sudden. I guess they could start sticking all of a sudden, so that's a possibility, but the OP watched them operate, and they seemed to be OK.

I'm thinking it's a timing issue. Since there is good spark, I'd be double checking the static timing to be sure it hasn't changed. timing can go out of adjustment if the points are loose...you'd still get spark, it would/could backfire, but probably would not start if off enough.

That's my vote. (sorry, Johathan).

Can it be a stupid thing like the carburetor no sitting well anymore on the intake? This engine run only 1hr and since the OP is not the guy who rebuilt this engine, I think a meticulous inspection need to be done step by step.

My swag is compression loss. Chunk of crud under an intake valve? There is a reason gas is spitting back into the induction system. Valve or timing. BTW, backfire is through the induction system and after fire is through the exhaust.

I remember working on a fresh rebuilt air cooled single cylinder motorcycle engine for a guy and the engine start and run perfectly until he reach his running temp then he start to backfire and finally he die. I check the timing , the valves the head gasket, nothing was wrong. I never found out what was really the problem but after I torque back the intake tubing and the carb he run perfectly well....Go figure. :bash2:

I just got home for the evening and, as stated, wont be home to even look at it again till Mon. But it's bugging the crap out of me every minute.

I mentioned the tractor was backfiring, but it was actually afterfiring. It was spitting gas out the carb and backfiring in the exhaust. I know the difference, it's just so much more natural to type backfire for some reason.

As for the static timing, I checked several times, I checked everything after changing anything. After the initial cleaning the points and slight adjustment, the timing never changed throughout the process.

One way or another, it has to be a compression issue. The fuel is now as it should be, the spark is now as it should be, the only missing major component of an old engine is compression.

Without breaking into it yet, I'm agreeing with the valve issue, whether out of adjustment, or not closing. The occasional puffs of white smoke and sometimes sounding like it might have fired, makes me think it's burning uncompressed fuel.
After having to adjust the carb, replace a less than great spark plug wire, and the issue in general, it's not going to surprise me if at this point I open up the engine and find out it wasn't in the condition he claimed it to be or he wasn't as good as he claimed to be, and I'm going to find a foreign object like a nut or snap ring jammed in the exhaust valve preventing it from closing.

That type of situation would explain the sudden change. I had something similar happen in a fresh rebuilt chainsaw once. Chunk of the old spark arrester sucked back in through the exhaust port and killed it. Tried and tried and tried to start it with no luck, opened it up all too late to find the piece had dislodged from the exhaust valve and destroyed the cylinder wall through multiple starting attempts. That's why I'm kind of leery (other than I just know better) of turning the engine over any more than I had to for diagnosing the problem.

You all got a few days to get your bets with Jonathan on the table... Lol
And I will get pictures up when I see my tractor in daylight again.