How Much Power Should a Cub Have?

[jpate831]

Hello,

My '47 Cub is "almost" perfect. It looks good, starts easy, and runs and idles great. And even when I get it under a load, it doesn't miss or anything, but it just seems weak. I know it's a Cub, and Cubs don't have a lot of horsepower, but I'd like to know if I'm getting the max power out of it.

For instance, it has the 48" mower deck under it, and taking off with the mower engaged is almost more than it can do at full throttle. Also, pulling a relatively light utility trailer empty up a small grade in 2nd gear seems to nearly tax it to its limit.

Like I said, it runs great. The governor seems to operate correctly. There's no sputtering or missing or anything like that. It doesn't smoke under any normal circumstances. It runs great, but it seems like it should have a little more power if it's going to be used as a tractor.

What got me to thinking about it was when I recently saw a guy mowing a field with his Cub. He was cutting what was borderline bush hog-worthy grass, and his Cub was just powering on through it like it was no big deal. I looked twice to make sure it wasn't an "A" or some other model, but I'm pretty sure it was a Cub. I don't think mine would have enough power for anything like that.

I don't have anything else to compare it to, except my '49 Massey Harris Pony. It's about the same size, but the Pony seems to have quite a bit more spunk. Granted the Pony has a recently rebuilt engine. I'm wondering if the Cub is needing one, too.

Thanks.

[Slim140]

You can always do a compression test and also put a timing light on it to make sure every thing is right there.

[w30bob]

Hi jpate,

I use my Cub (with front and back wheel weights) with a 59" Woods mower and it cuts high thick wet pasture grass without too much trouble. That's with the blades kept sharp. If I let them get really dull it's a bit of a different story, but that's not new news. No issue climbing grades......I think it would climb my barn wall if I let it. From your description it sounds like yours may need a little freshening up...........but the compression test will tell all. Just make sure you do it right, as the details matter. IE, throttle full open, a little oil in each plug hole and best done when the engine is hot, rather than cold....etc. You want to make sure you're getting that full 9 or 10 horsepower these monsters are known for.

regards,
bob

[jpate831]

I'm up for a compression test. Does anybody know what the psi values should be for a healthy Cub?

[w30bob]

Hmmmm.........if I had to guess I'd say 14.7 psi x compression ration minus a couple psi because nothing is perfect. I'd guess around 100. You guys want to give him the real number?

regards,
bob

[Smokeycub]

According to the Blue Ribbon Cub specs GSS1008 compression should be 120 psi. Anything over 100 is ok. Check timing, adjust the valves and I think you'll see a noticeable difference as long as your compression is good. The Blue Ribbon specs are listed above in the Quick Links, lots of useful data there.

[Glen]

Hi,
The ignition timing is also important for getting good power from a Cub. It needs checking with a timing light.
You didn't say if it has a magneto, or a Battery Ignition unit. You can check either type ignition with a timing light.
There is a procedure in the Cub owner's manual for setting the timing if it is a magneto.
The Battery Ignition timing is set using a timing light.

It could have a weak coil, and a weak spark. Or the points might need filing flat, or replacing. Or the spark plugs could be fouled.

[Landreo]

As Eugene says:
Do a full tune up.

Timing, points set and clean, compression check, fast idle rpm check, look at and gap the plugs, check valve adjustment, correct plug wires in the correct order, clean main jet in the carbs, clean the discharge nozzle in the carbs, etc..

Pull off or short one plug wire at a time and check for rpm loss if battery ignition. If you have a magneto then short the plug but do not remove the wire unless you ground the removed wire. Don't leave the wire dangling on a magneto. Each plug should have about the same rpm loss.

In the end you still may just have a worn engine but easy enough to check everything.

[John *.?-!.* cub owner]

Have you checked ignition timing, and if it is advancing as it should?

[wrz]

My 47 was't running when I bought it so cleaning the carb made it run lacking power. On this site I read about adjusting the valves which is pretty easy to do and found one cylinder had one valve with no clearance. It was like night and day how the performance improved. The compression test would show a weak cylinder that may need just a clearance adjustment of the valve.
Wm

[Indiana Robinson]

The question of "How Much Power Should a Cub Have?" has an easy one word answer... "MORE"...
OK, to be fair for most of the jobs it was originally designed for it does pretty darn good. It was designed to replace a horse or a mule or even a team on small farms, not an eight horse hitch.
The big giant power eating job is mowing with something other than a sickle mower. Bush-hog type mowers were unknown here in Central Indiana until about the mid-1950's. The Cubs did plowing, disking, planting and cultivating just fine. I always assumed that the PTO was so small and fast etc. first to keep cost down but to also keep guys from trying to pull combines and corn pickers with their Cub. Small belted stuff like corn shellers, hammer mills and buzz-saws were OK because it only had to drive the tool but didn't have to provide ground motion.
You want to always try to balance the load to the tractor and when you are doing so remember that when these early tractors were designed they were made to work best at speeds far below what we expect today.

[ntrenn]

Yep...cub should have more power..

Based on the specs...pony and cub should be indiscernable on power...62 cubes of l head vs 60...10.5 belt hp vs 10.4....

Pony plus model g total production 20% of cub production....just shows how popular the cub was...

[outdoors4evr]

Sounds like you need to put your cub on a dyno. Without some way to measure its output, I'm not sure how you could judge whether it is tuned properly for maximum output.
Without a dyno, maybe a "seat of your pants" measurement. Your cub should be able to run a 60" mower cutting 3" tall lawn grass down to 2" in second gear on flat (level) land.
Another option is to compare it to another well-tuned cub at a cubfest. I suggest entering a tractor pull.

[Mike in Louisiana]

Barnyard, Is the DYNO going to be at the Barnyard Bash ??????

[jpate831]

Thanks for the input, guys.

I filed the points and cleaned the distributor contacts a bit, but I didn't see much of a difference if any. I did notice that all of the plug tips are clean and a little white.

My next step was a dry compression test.

Here are the results:
#1 - 90 psi
#2 - 90 psi
#3 - 90 psi
#4 - 80 psi

Where should I go next? Wet compression test? Valve adjustment? I've heard 100 psi or better is good for a Cub. If so, is 90 and below grounds for a rebuild, or just a tune up?

Thanks.