Appears you've been busy with this. You may have already checked this, but I once had a problem similar. One of the main cables going from the battery to the starter had bad or loose ends on them weren't making good connections all the time. It would work fine one time and not the next. I had good cables so I soldered new the ends on. They had been compressed ends. It was a cheap fix and I didn't have any more problems after that. Hope this helps, good luck.....

 

I've been working on this all day, once again, today. I checked all the electrical connections multiple times, I even tried bypassing everything and hooked a jumper cable straight to the starter post itself but it still did the same thing. All the electrical connections are in great shape, even where each wire connects to its ends where you can see the bare wire (for example: where the pos battery cable end is stripped and crimped to the terminal), the bare wires are in brand new condition, they're all bright shiny copper still, EVERY wire connection looks like they did brand new, not a speck of corrosion or dirt or anything on any of them. I'm literally at my wits end with this thing. I've been dealing with this since October, MULTIPLE days a week, all with no success. I really need to get it going to plow the snow we're getting tonight but I have no idea at this point. Today I was sitting there looking at it, after adjusting the valves for the 15th time, and I started wondering if the new starter I put in was defective or something, it wouldn't be the first time I got a defective part from the store. So I removed the starter and took it apart. I noticed a few of the copper wires inside were broken, and since the tractor hasn't started since I put the new starter in I figure it must have came like that. Then I took apart the old starter, when I pulled it apart I saw that all the big magnets that line the inside wall of the starter housing were all broken in pieces and they were binding the starter up, keeping it from spinning, so I'm figuring that the original problem was the starter. Once I had both starters apart I took the insides from the old one and the housing from the new one and put them back together. Then, instead of mounting it back on, I set the starter on the work bench, hooked my jumper cables to the battery and just tapped the other end to the positive post on the starter and it spun beautifully!! So I mounted the "half new/half old frankenstein combo starter" back on the engine, thinking to myself that if it spun so great while sitting on the bench that I must have finally found the problem. Nope. Once it was mounted back to the engine I crossed my fingers and tried starting it. And once again, same thing, the engine would spin maybe a half a revolution, slowly, then stop and make a loud whine. If I keep trying to turn the key on and off repetitively it'll sometimes spin a half a turn or so, sometimes it'd spin a few revolutions (too slow to start though), and sometimes the solenoid would just click like as if the battery was dead (it isn't, I even tried my truck's battery). So its starting to seem like the new starter was bad when I bought it. BUT, on the other hand, that don't make 100% sense either, because when I put the new starter in two months ago and it didn't fix it I waited like a week or so then I tried adjusting the valves and when I was done it started PERFECTLY, it ran so smooth and sounded better than ever. Then, for the next two days I'd go out and try to start it just to make sure and I kept shutting it off and restarting it just to make sure it'd start again and for two days it started great, it spun fast and everything. But on the third day I went out and it was back to spinning really slow or not at all again. I've done everything I've mentioned at least ten times since and haven't gotten it to start again since. So, I figure, if it is JUST the starter then why didn't it work when I first switched the starter and why did it start perfectly after I adjusted the valves the first time and then went back to not spinning fast enough again. I've been an auto mechanic for like 15 years, so I do have some idea of what I'm doing, but this one has me TOTALLY lost. What really gets me is that if it was anything other than the starter then the starter should spin when I hook the jumper cables straight to it cause that bypasses everything else electrical. I just don't know anymore.

 

Have you checked the ground at the frame under the dash behind the steering shaft? Yours might be located in a different place but they get corroded, and loose contact because of the grass, dirt, etc. I worked on one for a guy before that you could turn the bolt with your fingers it was so loose. Its one of those out of sight, and out of mind things.

 

I kind of imagine you've checked all of this and I'm sort of reaching a little bit. A friend had a genset on a gold trommel and it started ONLY with a pull rope, NO starter at all. It got to where you about couldn't pull the rope like the engine was stuck, especially on a cold morning. He was using cheap oil in it and over time after a change, it just got worse. We got a good quality oil and changed it, problem solved.

You should be able to lay a starter on the bench and if working OK, it ought to turn free. The starter drive should be lubed and free as well. When bolted to the engine it should be straight and mesh well with the flywheel. Since you have set the valves I'd be surprised if they're not OK. That said, the engine should turn freely. If all these things are correct, it should at least spin the engine from cables direct from a battery on the bench.

 

I've checked every electrical connection like 40 times over. I checked the ground wire this morning when i was, once again, checking all the connections down by the selenoid. The thing that has me so confused is that when it first started happening back in october all i had to do was put a jump on it or tap the starter with a rubber mallet and it would start. I don't know if it was just coincidence that when it first started happening it would start after putting a jump on it or tapping the starter with the mallet, but that's what i'm starting to think, that it wasn't the jump or the tapping that made it start those times. So the very first thing i did to try to fix it was i changed the battery and the starter. So, if it was the starter from the first place it should have been fixed as soon as i put the new starter in, but it didn't. BUT, the old starter WAS shot, I know for a fact cause today i was getting so frustrated with it, i decided to take the new starter off and pull it apart to see if maybe i could see something wrong with it on the inside, it wouldn't be the first time i got a bad part from the store. When i took it apart I saw that the copper wires inside were broken in two spots. I then took the old starter apart and saw that the big magnets hooked to the inside of the starter housing were all broken into a ton of pieces and they were binding the starter up inside, so, that tells me that the starter was DEFINITELY bad from the start. So i tried taking the insides from the old starter and the housing from the new starter and i put them back together to see if they would work. When i had it back together i hooked jumper cables from the battery to the starter while it was sitting on the work bench and it spun perfectly, but as soon as i mounted it back on the engine it was back to not being able to spin the engine enough. I have another craftsman tractor with a 12 hp engine and i've had trouble with the starter on that not getting a good ground to the engine block so I tried hooking a jump wire from the starter directly to a ground just to make sure it was grounded enough, no change. Still wouldn't spin fast enough. Whats most confusing is that when i first changed the battery and the starter it didn't fix it, but a week or so later when i adjusted the valves the first time it started right up perfectly. I turned it off and on like 30 times in a row just to make sure it wasn't a fluke. Then for the next two days i didn't use the tractor at all but i still went out to make sure it would still start and for two days it did. PERFECTLY. It even ran smoother and quieter than ever. So i finally breathed a sigh of relief that it was finally fixed. But on the third day i went out to use the tractor to plow snow and when i turned the key NOTHING, right back to not spinning fast enough or not even at all. I've rechecked the valves so many times since. So if it was just the starter it should definitely be fixed by now, if it was the compression release then it should have stayed working after i adjusted the valves, if it was an electrical connection then it should have spun when i hooked the jumper cables straight to the starter cause that bypasses every electrical connection, if it was the battery it should have worked when i tried jumping it or when i tried using my truck's battery. I was starting to wonder if maybe there was something wrong down by the crankshaft or something cause the engine to be hard to spin, but that can't be it cause i can spin the engine by hand pretty easily AND if it was something like that then it wouldn't have started so great for the 3 days when i adjusted the valves. This is driving me so nuts, NONE of it makes ANY sense whatsoever. And even if it was that i got a bad starter right from the store then why did it start perfectly those three days and then go back to not working? At this point i'm not even concerned with it starting, i just want the starter to spin the engine fast enough. Even if it was something stupid like the ignition kill when you get off the seat then it would still spin the starter, so i know its nothing like that. I don't even know what to try next.

 

Welcome to the forum
The next time it does it,try this:
Using a good set of jumper cables,connect the neg. cable to one of the engine mounts,and the other end to the neg battery post,and turn the key. If it rolls/starts well,add an extra ground cable.
If it still won't roll/start,put the + cable of the jumpers on a ground (- jumper cable still on engine),and the other end to the mount plate of the SOLENOID.
If it rolls/starts,the solenoid isn't getting a good ground.

 

you seem to have gone through a lot with this. I wonder if you put a volt meter to see how much power is being sent to the starter you might narrow down if it is electrical. The only time I've ever seen a starter work sometimes and not others, or turn a motor slow - it was an electrical connection, or a weak battery.

 

Find the problem yet?

I have the exact same issue. 10 yo DYT4000 HST w/18.5 HP single cylinder Intek. Lethargic starting. It has NEVER started enthusiastically since day 1. In summer its lazy but eventually will fire, but when it gets cold it just wont crank. It makes intermittent slow turns, hesitating for a couple of seconds at each compression stroke and then eventually (after 8 revolutions or so) it ignites the accumulated fuel in the exhaust for a real wake up call.

The 16 month old (its predecessor did the same thing) battery shows good voltage, has been tested and the charger refuses to give it more than trivial current, so battery seems good.

And of course you cant push start a HST or I would just do that. (Can you? I was taught you couldn't so Ive never actually tried it)

Jump-starting does not help even when connecting directly to the starter post, bypassing on-board battery and relay (which makes it look like a bad starter). Yet, replacing starter does not fix the problem.