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I picked up an early 90's lawn boy awhile back. It is an F series engine that didn't run at the time. I put a new coil on it and cleaned the carburetor and took the muffler off to check exhaust ports. It started up but doesn't run real smooth like
all my other F engines and it smokes a lot. I told my wife I can fog for mosquitos while I mow. The smoking does slow down after awhile but you can always see smoke coming from underneath. I did notice that when I had the carb off the reed valves had some rust or some kind of corrosion on them but they sealed up just fine. Does any one have any idea why this mower would smoke so much?
Thanks.
Jerry

White smoke or black smoke? If black likely engine is running rich. Is underside of deck oil covered.....I have heard that it may be a leaking crank seal on other discussions. What are you using for oil and mix ratio?

If the mower sat for a long period of time, you may have a large amount of oil sitting in the crankcase. If that is the case, it should clear up after about 30 minutes of running. As sail check your fuel/oil ratio. I suggest you use Opti-2 oil, because you don’t have to measure and smokes very little.

It's white smoke. I think I changed the crank seals. I almost always do when I buy one to resell. I use outboard motor oil at 32 to 1 and sometimes Amsoil at 50 to 1. I have also tried adjusting the altitude screw on the walbro carb and it doesn't seem to change anything. So I didn't know if it might be the rings or the reed valves or what. I have tinkered around on several Lawn Boys over the last few years but never had this problem before.
Thanks.
Jerry

Outboard oils air meant for water cooled engines, not Lawn Boys, which run hotter than mowers. Lawn Boy fuel/oil ratio should be 32-1 when using standard 2-cycle oil.

I have been using Amsoil Saber for years. I ran out one day and couldn't get any more for awhile. The only reason I bought the Evinrude/Johnson oil was because I have read on this forum several times that Lawn Boys should use outboard motor oil TCW3 rating. But this can't be an oil problem because none of my other 8 mowers smoke.
Jerry

I think I will be using Shell Nautilus 2 stroke oil when my supply of Lawn Boy oil runs out. It is recommended for air cooled engines. Alternatively, Castrol Go 2T motorcycle oil.

Letting the crank case gases back into the intake will give a pretty rich mixture on these, and worn carb throttle shaft will allow this too with the enrichment port set up for wide open throttle. I'd change those reed valves first off.

Tom, the crankcase is part of the fuel delivery system on this mower. Oil in the fuel lubricates the internal parts of the engine before the mixture leaves the crankcase and enters the combustion chamber. Replacing the reeds won‘t change or solve his problem.

I don't know if it will help...see page 3-15 excessive smoking in the following link to another lawnboy forum

Rivets said:

If the mower sat for a long period of time, you may have a large amount of oil sitting in the crankcase. If that is the case, it should clear up after about 30 minutes of running. As sail check your fuel/oil ratio. I suggest you use Opti-2 oil, because you don’t have to measure and smokes very little.

Click to expand...

100:1??

slomo

Thanks for your replies.
Jerry

Rivets said:

Outboard oils air meant for water cooled engines, not Lawn Boys, which run hotter than mowers. Lawn Boy fuel/oil ratio should be 32-1 when using standard 2-cycle oil.

Click to expand...

Actually Lawn Boy specifies in the owners and service manuals to use a quality TC-W3 rated oil when not using Lawn Boy brand 2 stroke oil.

L8R,
Matt

Another thing to check is the muffler. It could be loaded with oil sludge and is burning it off. Pull the blade off if necessary, then pull the muffler. If it’s a two piece muffler, split it apart and use some carb/brake cleaner to clean the sludge. If it’s a one piece muffler, hopefully you have a gas grill with a side burner, and sit it on the burner. Set the burner on medium and pretty much let it cook until the smoking stops.

L8R,
Matt

I didn't look at the diagnosis but I can tell you that excessive smoking is too much oil in the combustion chamber. Now this can be from either an overly oil-rich mix or simply too much fuel getting in with a correct mix. The choke might be on. The air filter might be restricted.