2 cycle LB runnging rough

[dlundblad]

A 2 cycle Lawn Boy was given to my dad last fall by one of his friends. He bought it at an estate auction last Fall for $25. IIRC, it sat for about 10 years. It has a bagger and it self propelled (very primitive design) making it ideal for our small yard. I finally got around to firing it up last weekend and it runs very rough. It will run fine one minute then sound like it is getting ready to die the next.

I am guessing the fuel filter is clogged/ gummed up. I am contemplating on running sea foam in it as well. Hopefully those things combined with it running for a good hour or so will clear it all up. We shall see.

It also smokes very bad.. This is the first 2 cycle mower I have seen in action and compared to our other 2 cycle equipment, its quite a bit of smoke. What oil to fuel ratio is best? 40:1? 32:1?

Not sure on the model #, but it looks like this one, but without the offset wheels. 1980 something.
Here

 

[Bluestream]

Carb needs rebuild; save your money on the sea fome, that's just not going to work

 

[lawman1909]

Youtube "Jon3800". He is a wiz about lawn boys and some of his info has actually helped others with LB problems

 

[dlundblad]

Originally Posted By: lawman1909
Youtube "Jon3800". He is a wiz about lawn boys and some of his info has actually helped others with LB problems


Ironically just heard him being mentioned in another video. Lol. Ill give him a listen.

 

[29662]

Drain and flush the tank if you haven't already, replace fuel lines and filter. Try a little Techron or SL-1 in it before you try rebuilding the carb.

I LOVE 2 cycle lawn boys mowers. Properly cared for they will last for years. Lawn boy recommended a 32:1 oil ratio. Use non-Ethanol gas if its available.

 

[dlundblad]

It appears to be an 8291 btw.

 

[wally6934]

Perfect timing, last weekend i went through a clogged carburetor on my lawn boy and i think the Sea foam was helping. I was hoping someone else could try the experiment.

Last year a friend gave me this lawn mower and it did not run. Last weekend i thought i would try to fix it. It had spark but would not fire. I took the carburetor apart and it was full of gas and clearly gunked up with dark stuff that had a consistency of thick peanut butter.

I gave it a once over clean up job but did not dig out all of the dark gunk. I then reassembled it and put in fresh gas with the recommended 2 oz of sea foam per gallon and gave it a try. It did not fire even once. I pulled many times and primed many times but it never fired and the plug never got wet.

I then searched the internet for detailed rebuild instructions for my model and found several good pictures of were the passages and holes were.

The next day about 20 hours later i took the carburetor apart again and started looking it over. The thick gunk was now more liquidy and much easier to clean up. I took all jets and needle seat out of the carburetor and blew compressed air through it and uses a fine wire to poke through the jet holes. After reassembly the lawn mower fired up with the first pull.

The bottom line is, i credit the sea foam for loosing up the gunk, and i might have lucked out if i had let it sit for a few more days and it would have not needed the second rebuild.

I was hoping you would try the experiment with your lawn mower. In your case since you can get it to run you can get the sea foam all the way through the carburetor. This is what i think you should try.

1 Dump old gas.
2 Add new gas with 2 oz of sea foam per gallon.
3 Run mower for 1 min or so.
4 Let it sit for one day and run again for a minute or so.
5 Repeat for several days and see if your problem goes away.

 

[chestand]

Rough running/smoke in F series engines can be caused by a dirty air filter, vacuum leaks at the carb to engine mount and/or a carboned up muffler or engine exhaust ports. On the F engine, to get the muffler off, the blade needs to come off, then the blade adapter. The adapter should pop off with a sharp blow sideways with a hefty hammer. If it's balky, heat it with a propane torch and try again. Once the muffler is off, a coathanger can be used to break carbon up or you can heat the muffler. One of the best ways is to lay the muffler on a pile of charcoal. It will smoke though, so be prepared. Clean also the three exhaust ports on the engine beneath where the muffler mounts with a wooden dowel and carb cleaner. Carboned mufflers/exhaust ports typically are caused by running fuel mixed with non 2 cycle oil.

 

[dlundblad]

I took the carb apart and cleaned it. I installed the fuel filter (didn't originally have one) and drained the tank of all the floating crud.

I had it running perfectly yesterday for about 10 minutes. I turned it off then restarted it and it sounded like it was idling at low throttle and eventually died. It did that the rest of the day.

Im going to try cleaning the carb again before getting the rebuild kit. I also noticed there is some more stuff in the tank... I thought I got it all! Ill check the lines as well as they are all brittle. This is my first lawn mower service so its a learning process.. Lol.

Chestand: I tried getting to the muffler yesterday, but failed. Took the blade off, but the square piece (blade adapter?) on the shaft that holds the blade in place would not budge. I even shot it with PB blaster and let it sit for about an hr. Ill retry and let you guys know. Thanks

 

[chestand]

You're right. The blade adapter is the square piece that the blade sits on. It's a taper fit on the crankshaft. If you have a propane torch, heat the adapter throughly then while it's still hot, give it a sharp sideways rap with a large ballpeen hammer or a hand held sledge. That's how it remove the ones that have never been off. Good luck.

 

[dlundblad]

I was able to heat up the adapter like you said and it worked well. I cleaned the muffler out and saw 2 of the 3 exhaust holes coming from the engine were about half way clogged. Definitely thought I was onto something. I then replaced the fuel lines with clear (temporary) .25" rubber hose and started her up. I also took carb cleaner and an air hose to the carb. It was spotless.

It ran for a few minutes and then died. I noticed fuel dipping from the air filter so I feel its definitely the carb as mentioned earlier. Not sure if I should get a rebuild kit or just a new one. $10 vs about $50.

Darn. I was really hoping it just needed cleaned rather than dumping more money into it. From what I have read on LB forums, the F series engine is pretty decent so Id hate to see it get scrapped.. Lol.

 

[chestand]

Don't scrap it. The F engine LB is the best engine LB ever made and despite what you're experiencing now, they're smooth, powerful and fairly bulletproof.

Something else I should have mentioned: crankshaft seals. LB p.n. 611396. Two stroke engines need seals that are in good shape to run well because they have a pressurized crankcase. The seals are like $4 each and are easy to install - one on top and one on bottom. Look at mytractorforum.com and search the walk behind mower section about replacing crank seals on an F engine.

 

[dlundblad]

Originally Posted By: chestand
Don't scrap it. The F engine LB is the best engine LB ever made and despite what you're experiencing now, they're smooth, powerful and fairly bulletproof.

Something else I should have mentioned: crankshaft seals. LB p.n. 611396. Two stroke engines need seals that are in good shape to run well because they have a pressurized crankcase. The seals are like $4 each and are easy to install - one on top and one on bottom. Look at mytractorforum.com and search the walk behind mower section about replacing crank seals on an F engine.


I appreciate the quick reply.

Just became a member of that forum the other day actually. Lol.

I got it running again and noticed it runs better without the air filter, which I consider to be clean. Does this point to the carb being the issue as well?

I also called the local mower dealer and asked about a carb rebuild kit/ new carb. They said the carb was never offered in full kit and everything is sold separately, which I have found on the web. They also said rebuild kits were never offered for that carb. Not sure how true it is, but it explains why I am having a heck of a time finding them.

 

[chestand]

The fact that it runs better w/o the air filter means it's running rich. The F air filter is a foam rectangle, it's a wash with soap, dry and re-oil process to clean it. Make sure you take a rag and wring out as much oil as possible afterwards. Possible other reasons for rich running include carb needle valve leaking or not sealing, incorrect float height or float leaking so it's no longer floating.
I've never seen a true "rebuild kit" for a LB 2 cycle. Common carb replacement items include the needle valve, occasionally the float, and the bowl to body and body to engine gaskets. Have you checked spark? Replaced plug? (Champion CJ-14 BTW). Weak spark or bad plug can do some of these same things.

 

[dlundblad]

Originally Posted By: chestand
The fact that it runs better w/o the air filter means it's running rich. The F air filter is a foam rectangle, it's a wash with soap, dry and re-oil process to clean it. Make sure you take a rag and wring out as much oil as possible afterwards. Possible other reasons for rich running include carb needle valve leaking or not sealing, incorrect float height or float leaking so it's no longer floating.
I've never seen a true "rebuild kit" for a LB 2 cycle. Common carb replacement items include the needle valve, occasionally the float, and the bowl to body and body to engine gaskets. Have you checked spark? Replaced plug? (Champion CJ-14 BTW). Weak spark or bad plug can do some of these same things.


Ill check the mentioned things. Thanks a lot.

 

[chestand]

Couple of other things, 3oz of quality 2 cycle oil per gallon of gas is the mix I run. That's approximately 40:1. If it's primer start (it probably is if it's a plastic carb), make sure the primer bulb and hose are in good shape with no holes. Also, check to make sure the carb hold down screws are tight. Not screaming torqued to 50 ft./lbs or anthing, but good and snug. You're dealing with most likely a plastic carb base flange and you don't want to warp or crack it with excessive torque.