That's a pretty uncommon mower: It's an IH balanced head, pretty sure it's a model 100. But the vast majority of the model 100's were three-point. A few were fast-hitch, and a few (like yours) were drawbar mount.
As far as adjustments go, all the usual apply. Here's part of a reply I wrote to another chap having trouble cutting with his. It sounds like you've already looked into much of this, but make uber, uber sure your register is set correctly and your hold-downs are holding the knife tight to the ledgers.
For Maintenance:
- Sections need to be kept in good shape. If yours is a 7', buy a new knife. AI makes aftermarket under-serrated ones that'll fit yours, and it'll pay you back in spades (any dealer can order AI products).
- Make sure your wobble mechanism is tight, well-lubricated (regularly during use), and has no slop (a little bit of slop/play makes a big difference in how it cuts).
- Make sure your ledgers on your guards are sharp, square, and all level with each other.
- Make sure your hold downs are good - holding the knife nice and close to the ledgers.
- Make sure your knife & bar is registered correctly. This is very often overlooked, and if it's not right it won't cut worth a dang.
- Set the lead on your bar - the far end of the bar should be just a tiny bit ahead of the pitman-end when mounted on the tractor.
When Using:
- Don't cut through hay that's already cut - it'll plug instantly. You'll get pretty good at lifting the bar right at the end of a run, and dropping it right at the start.
- Sometimes a little speed helps, sometime it hurts. Play around and see what works. 90% of the videos you see on Youtube of guys with sickle mowers are cutting far too slow. If you have everything adjusted right, there's no reason even an old pitman mower can't plug along at 5-6 MPH just fine (as long as the hay isn't down or lodged). We use some 9' JD 350 mowers for a lot of hay at our Northern farm, and you can zip along in 6th high at 8-9 MPH all day with it.
- Keep your lines straight when possible and watch your turns. Often better to lift and loop around to the left and drop back in square rather than make a sharp right. If you make a sharp right, the end of the bar will be travelling very, very slow (possibly even backwards, if you turn sharp enough). Without decent forward momentum, the end of the bar is more likely to plug.
- Down or lodged hay will often be a nightmare, despite your best efforts. Best to cut before it has chance to get knocked down.
- Don't cut when it's damp (even if only very slightly) - wait until all the dew's off.
- If cutting alfalfa: It's a completely different animal than other types of hay, and modern alfalfa strains are a lot different than your grandfather's alfalfa. The stems of modern varieties are a lot tougher and higher yielding. You can cut it with a sickle mower just dandy, but it'll take forever for the stems to dry down. By the time the stems are ready to rake/bale, the leaves will be bone dry and shattering. You can get around this a little if you rake when a little dew's still on, but it still won't be great. Better to buy a crimper to pull after the mower so it all dries evenly (although crimpers can be a complete PIA). If you are cutting with a sickle mower and no crimper, it helps to cut long before any of it even starts to think about blooming: the stems aren't as tough or waxy. This might even be better for your RFV value needs, depending on what animals you're feeding. Cutting early is perhaps good for cattle (especially dairy/lactating), but probably a little rich for horses (depending on alfalfa percentage).
And keep in mind that cutting well and fast with a sickle mower requires skill, finesse, and proper maintenance. It's not like a bush hog; you can't just drop the bar at the start of the year and go. Around here, sickle mowers get bought and sold at a crazy rate: I've been watching some of the same sickle mowers pop up on marketplace from different sellers every year. It's mainly horse people: They think one will be great to maintain their pasture, buy one, but aren't prepared for the effort and finesse it takes to keep one cutting well, and sell it to the next guy.
