slow cranking

I have a 1950 TO 20 that I am trying to get it running again.,
With the sparkplugs installed even with a newly rebuilt starter
and a hot battery the starter seams to drag. But with the plugs
removed it spins like crazy. I have removed the valve cover and
all the valves seam to be moving freely. But if I install one or more plugs in any of the other cylinders it gets worse.

Also with new coil, points condenser cannot get any spark through the points

Even if no spark it should turn over fine,

I would pull the battery cables off check each end for corrosion I have seen cables look good but have corrosion inside the cable,

If you buy new cables get #1 size cables you need all the power you can get to start these old tractors, old welding cables work good if you
could find a set to make up, I got my #1 size cables at Napa,

Also out of time can make it turn over slow,

So many things could be wrong, may have to check amp draw of rebuilt starter, it maybe defective

Let us know what you find wrong

I am having the same problem. Hope to have solved it tomorrow when I install new spark plugs and try to start with the battery
fully charged. I discovered that a 6 volt battery needs to read 6.30 or so on the multimeter for it to be 100% charged. Less
than that results in the % of charge greatly reduced. I have replaced so many elements of the charging system and am still having
problems. My starter needed to be shimmed as it was making a terrible racket when I tried to start.

Let me know if you have success.

This tractor was changed to 12volt years ago, and has been stored inside for
15+ years. It was running badly before it was stored.
I am going to pull the head and check the valves and cylinder walls
for gouges ect. I am leaning toward the timing being off because with all
the spark plugs removed the engine turns over very fast but add any spark plugs
and it slows down and sounds labored.
thanks for your help.

If you have the crank for it, try turning the engine with that instead of the starter. If ir turns easily it will isolate the problem to the starter or electric parts.

If you determine that the engine turns hard, you know better where to start digging for the problem.

If the engine turns easily with the crank, hook jumper cables from the battery to the starter. If the engine then spins easily you know your starter is good and the problem lies with the battery connection, the cables, or the switch. If it doesn't spin that way, try jumping from a different battery. Little steps to narrow the problem search.

No need to pull the head...

The reason it turns slower with the plugs in is because the compression is making it harder to turn, perfectly normal.

You can check for improper timing by simply pulling the coil wire and trying the starter. If it cranks better, the timing is fast. If no difference, the timing is not the problem.

One thing you might try would be to put about a teaspoon of light oil in each cylinder, spin it through before putting the plugs back in. This would lube the cylinder walls sense it has been stored. Also the bad running, could have been running too rich, washed down the cylinders. Check the air filter mesh for clogging. And check the oil for gas contaminaton, that can make it difficult to turn.

But the real problem is most likely electrical. With 12v on a 6v starter, it should spin really fast. You'll need a volt meter to check for the problem. Possibly the battery is not delivering the power, check across the battery posts (not the cable ends) WHILE CRANKING. If the voltage drops below about 9 volts, the battery is under charged or bad.

If the voltage at the battery stays high, keep checking the voltages one connection at a time all the way to the starter. Do all tests WHILE CRANKING. That puts the system under a load.

Two common problem areas are where the ground cable connects to the sheet metal. Better to move it directly to the engine block. The other problem area is the starter contacts on top of the transmission. While checking, feel for any hot connections. That is a sure sign of a bad connection.

If you trace good voltage all the way to the starter POST and the starter CASE (ground), and the engine is still turning slowly, revisit the starter. Even though it was rebuilt, things happen. There could still be a starter problem.

I got it running. with a little more oil in the cylinders, and valves.
Also with all the posts about grounding and battery cable size.
I finally installed a battery. Instead of just using jumper cables.It gradually started to crank faster.
MY spark to the points problem was solved by changing the condenser and by passing the new volt meter.
Will have to work on this soon.
With some fresh gas it started right up.
Glad I did not pull the head.
Now its a new water pump, fixing the brakes (never worked),
checking the clutch and repairing hydraulics.

Thanks Dee