Maybe this will help somewhat, but I would guess the most likely cause would be that the oil pump is injecting too much oil.

Another possibility is the carburetor running very rich, although this may be unlikely if it is definitely oil smoke that you are seeing.

There is a check-valve in the oil pump that could go bad and let oil leak into the cylinder when the mower is not running. If that failed, it would smoke alot mainly near startup, but should stop smoking after warmup if this were the issue.

There is an M-series repair manual available for free download at Lawnboy.com. That might give you some additional ideas. Go to Lawnboy.com then click "Request operator's manual" link on the lower left hand side. Then enter your model of M-series find the Manuals Tab on the resulting screen and download the 174 page repair manual.

Another thing you might want to try is to drain all the oil from the oil tank, and just run it for a while on 64:1 premix from the fuel tank. This might let you determine if the oil pump is just pumping too much oil. If you decide to test this way, you'll have to disconnect the low oil warning switch from the wiring harness. (It attaches to the wires from the bottom of the oil tank.) The mower will run with this disconnected. If it smokes less this way (after you've let it run long enough to get the oil out of the lines) then you could just choose to abandon using the oil pump and run premix only if you didn't want to repair or adjust the oil pump. Good luck getting things diagnosed...

Adkinsca covered it well. Have you run the mower long enough (mowing) to really clear out the engine under load? I agree with the check valve theory for startup, but then it would clear up after 10 minutes or so of use. There is an oil pump setting in relation to throttle control speed, but the pump should pump full volume only @ w.o.t. Perform the vacuum check on the oil check valve first, soak the cylinder good with SeaFoam, maybe switch to some good synthetic oil, and retry. Maybe the owner put standard engine oil, or something worse in the oil tank? When I first ran mine this year, it hadn't run in well over a a year, and it smoked a bit for the first 5 minutes or so, but then cleared up nice as it should. My first test would be to ensure the right oil is in the tank and go from there. Let us know how you make out indy.

Thanks fellas, I let the engine run for about five or so minutes under no load on the parking lot of the dealer that has it for sale. What may be the big issue is it has sat for a month or so without being run.
I noticed the oil tank was completelly full of some kind of oil but you never know what kind.
If I choose to pick it up, I'll definatlly be checking the oil pump for function and draining the oil in the tank for piece of mind.
As for cleanliness, I'm pretty fussy so a good washdown is a must and a good going through will be in order for the "M".
If I decide to buy I'll post some pictures of it.

B.T.W, are parts for this as expensive and hard to get as everyone says? Why? What if I need the oil pump check valve, is it going to cost a mint? If so I just may pass on this because the last thing I want is some older machine that is going to nickel and dime me to death. I have virtually no "M" parts in my descent inventory.

Thanks Adkinsca and Echoman, Neal

m veteren here-dont worry about the smoke-it shows the oil injection sys is working. as for parts-yes they are rare and horrendously expencive but for now there are usually parts on ebay from time to time. in short i dont recommend this mower for the causal user-its like owning a rare finiky vintage car

Is the mower in good shape? If the price is right $100 or less, I'd buy it. These mowers were built tough, basically for everyday commercial use. I like most M-owners, don't use them much other than to keep "things right" on the inside in fear of something maybe breaking and not being able to find that particular part. I'm actually surprised as to all of the M mowers still out there, and being used. Seems to be a good "used" inventory or parts still available. All mine needed was a little cleanup detail, and a new coil and it runs great! It is a bit on the heavy side compared to most Lawn Boys, but the power and cut are top notch. Even if you got it running right, which I'm sure you will since the injection system is realitively simple in design and function, you can always get your money back out of it if you don't like it. I think it's 1 of the many great "novelty' LB's to own! I gave $25 for mine and another $45 for the coil and put a new blade on it, but condition wise, I wouldn't see why $300 or $350 couldn't be had for mine due to condition. I'd rate mine and 8 out of 10. I say buy it. You really don't have much to lose.

Mine does the smoking every once in a while. The smoking will go away after a few minutes. Sometimes it does take more than 5 minutes though.

Its a model # 10591 1994 year. $75.00 asking price but I've bought and done some contracting for the dealer so I hope to do some bargaining and some trading for it in the next few days.
I work for a living and can't always drop what I'm doing to do business for a collectors idem. Now if it were for my business that would be a different story. Like most other Lawnboy and Toro fanatics I feel that I would like to have this machine in my collection for looks and not so much as for use. I am confident in my mechanical abilities to do any major or minor repair.

I keep thinking I'll run into one at a garage sale or auction for cheap but this is the first to come along for sale in several years so I need to act fast if I want it huh?

Thanks, Neal

As long as it appears solid, and not dropped off the back of a truck, or stored outside, I'd buy it. I'm sure you'll like it for occasional use as well as a conversation piece and just looing at it's different design. Before you buy it, start it up and check out the gears to make sure it engages smooth and pulls well. Most parts are still available for the trans should you need anything other than a new belt. I have no reason to believe you can't get the engine to clear/tuned up, to run as it should. Let us know if you do buy it Neal.

man my "M" has been sitting in the shed for two years because i can't find a transmission for it torq tuff
i believe, they are rather futerist looking

So the tranny is different than that of a 10515 or similar staggered wheel three speed?

Are there differences with O.M.C built versus Toro built?

This "M" I was looking at said Bloomington, MN on the model tag so I presume this was in the "transition" era of the omc/Toro buyout.

Neal

The 10591 is a late version of the M series. It has the updated wheel clutches that freewheel in reverse.(good) Not a transition unit. (If there ever was such)
The transmission is different from some other Lawn-Boy models because it is made by Tuff-Torq. Tuff-Torq makes a great product so it should be fine.
adkinsca put me on to the differences between the early M units and the later ones. That difference being the wheel clutches. We both converted our early M series units to later style wheel clutches. They are much easier to pull backward with late model wheel clutches.