You most likely need to oil it more. It's common for these old machines to develop stitcky parts by dried up oil and grime accumulated over the years. You have to detect all oil points, apply a bit of oil to all of them, then run the machine a bit, move the stitch length lever up and down, a round of oil on every oil point and repeat a few times.

It can be caused by built up dust and lint under throat plate - feed dog and bobbin area. They often need a good cleaning too when taken out of long term storage. Slide the bobbin plate completely off, lift the lever slighly up and towards you and the bobbin case will come out. Unscrew the throat plate too and clean out all dust and pieces of thread.

All the holes on top of the machine are oil points, and there's several under the base and behind the face plate. Oil every hinge, joint and moving part that runs against another. Remember to oil needle and presser bar too, the area where they move up and down in the cast iron part can freeze up too.

Pay particular attention to the parts involved from stitch length lever to feed dogs. At maximum stitch length turn the hand wheel and they are easily detected. The end of the rods each have an oil point or two, as well as the moving parts under the feed dogs.

Hi Sporter, welcome to the board! Does your 99 have this style of stitch length selector?

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If so, then you haven't missed anything - there is no way of returning to the same stitch length except setting it manually every time. It's not a great design, which is probably why it was phased out after a few years.

I thought the numbers gave accurate stitch length? That said, I haven't used these much. The machine I kept was the old type with the stitch length knob and no reverse. The stitch length function will get irregular on these if they aren't cleaned and well oiled. The most common is to get stuck on one stitch length, or a fraction of full capasity stitch length.

The numbers are reasonably accurate, but it's much nicer to be able to flip the lever down without thinking, and have it be the right length. Later models do this by having a set screw either in the lever or beside it.

Sporter, if I were you I would probably tape a paper clip right below the lever when it was at the length I wanted. You would have to move the paper clip when you wanted to change the stitch length, but it would work.

Singer 99/66 feed dog adjustment forward and backward
 

I know this is a long time ago now - but my answer might help someone now. Set the machine on its longest stitch length and lay the machine on its side/back, hinge side down, and locate the link from the top of the machine to the long connecting rod that goes across under the machine to the feed-dog area. If the hinge side is down the linkage should be located in the top-right (upper) corner of the underbed area as you look at it.

Loosen the nut on this linkage (it will be facing toward the inside of the underbed area - in the same direction as the rod). A 3/8” AF spanner is about right, the ring ones are easiest. Hold the bolt still with a screwdriver while you loosen the nut - otherwise the whole thing might turn, preventing you from loosening the nut. You don't need to remove that nut all the way off - it only needs to be loose enough so you can turn the bolt freely. That bolt is an eccentric and as you turn it you'll see the position of the feed dogs in the cover plate slots forward-and-aft is changed.

Test the position by turning the balance wheel until the feed dog is at the far end of its travel. Use the screwdriver to turn the bolt until the feed dog approaches the end of the slot in the cover plate. Turn the balance wheel for a full stitch cycle to make sure that you've got your adjustment just right - as you know, you don't want the feed dogs to catch or bang into the cover plate slots at front or back.

When you've got it just right (full length of travel for the whole stitch cycle and no banging into the cover plate slots anywhere) tighten the nut while holding the bolt still with the screwdriver so that the eccentric part of it doesn't change position and mess up your adjustment. Test for a full stitch cycle again just in case your bolt moved while you were tightening it. If it did, just loosen the nut and try again.

Thank you Megan Mils this may indeed help someone in the future. Whet does AF mean in front of spanner?

AF means "across flat". When you have things like hexagons you can measure between two opposite flat sides or between two opposite points and the distances are different in each case. Saying which it is helps people know which size to use and spanner sets are typically sold as being "AF" if that's the way they're measuring across a polygon like a hexagon.

I've also just found a vid where someone demonstrates the same idea on a different model Singer. For that one the placement of the rod under the bed of the machine that has the "bolt and nut" on it is slightly different but aside from that everything you need to do to make the adjustment is the same. Search for "Set feed dog lengthwise in Needle Plate - Singer Model 301A". You can speed it up if you want by pressing <Shift> + <.> while the vid is playing. You can press <Shift> + <,> to slow it down again. (The more times you press the more it slows it down or speeds it up.)