Lawnboy L21ZPN

[SGRIFF144]

Recently I purchased a carb rebuild kit and replaced all of the gaskets, welch plugs, and needle. The mower has spark and will run on starter fluid until the starter fluid is used up. Gas flows into the carburetor bowl. Gas flows with the float in the down position and ceases when the float is elevated. ( I believe this is correct) I am wondering what the next step in carburetor troubleshooting should be. Thanks for the help.

Sean

 

[Phototone]

Did you unscrew the main jet from the bottom of the plastic carb and clean out all the tiny holes? (Not the needle and seat of the float) You have to remove the filter screen from the bottom to gain access. If you are careful you can reuse the screen. The screen is just friction fit over the bottom opening, but be sure to clean the screen with carb cleaner. There are several holes in this jet that cannot be even seen unless you unscrew it and remove it from the carb. It is in the center bottom of the carb, the round doughnut float sits around it. You are not getting fuel, and the only thing it could be is a jet blockage..which you cannot clean without removing the jet tube from the carb. I like to run a small wire thru the whole thing, including the side holes, then use aerosol carb cleaner while holding the jet in my hand and making sure the carb cleaner shoots out all the holes. You can use a flat-blade screwdriver to unscrew the jet-tube using the slots you see on the bottom.

NOTE: This advice is basically the same for most Lawnboy metal carbs.

 

[robinb66]

Also you might try checking to make sure there are no leaks between the carb body and the crankcase, lawnboys are really picky about air leaks!

 

[SGRIFF144]

So as you mentioned, I removed the carb and cleaned the main jet with a small wire and carb cleaner. I reassembled the carb making sure the gaskets lined up and the mower started on the first or second pull. It has issues with over revving, so I assume the next order of business is to fine tune the carb? From what I have read, the governor spring is supposed to hold the butterfly open and the air vane is supposed to work against the spring by closing the butterfly...is this correct? Also, I read that the max RPMs are supposed to be 3300 (I have to double check this), but how does one measure since there is not a good place to apply a tachometer to the crankshaft?

Thanks again for the help!

Sean

 

[Two-Stroke]

So as you mentioned, I removed the carb and cleaned the main jet with a small wire and carb cleaner. I reassembled the carb making sure the gaskets lined up and the mower started on the first or second pull. It has issues with over revving, so I assume the next order of business is to fine tune the carb? From what I have read, the governor spring is supposed to hold the butterfly open and the air vane is supposed to work against the spring by closing the butterfly...is this correct? Also, I read that the max RPMs are supposed to be 3300 (I have to double check this), but how does one measure since there is not a good place to apply a tachometer to the crankshaft?

Thanks again for the help!

Sean

Check out this thread about an inexpensive tach by one of the regulars here in the LB forum. I haven't bought one yet but it sounds like a good deal.

 

[impalass]

Check out this thread about an inexpensive tach by one of the regulars here in the LB forum. I haven't bought one yet but it sounds like a good deal.

For your model the rpm IS 2900 +/- 300.

 

[SGRIFF144]

Thanks again for all of the input. The mower runs great with some minor adjustments of the governor spring and I will be sure to order a tachometer to fine tune the RPMs. However, when running the mower, gas/oil mixture appears to be leaking from the crankcase. I believe it is dripping down the crankshaft and being spun off in a circular fashion. I replaced the upper and lower seals, but apparently my installation was inadequate (I'm not sure if it is possible to install the seals backwards or not). I set the seals in place with a piece of PVC pipe slid over the crankshaft and tapped with a hammer. Maybe oil was applied to the outer edge of the seal and prevented a good fit between the seal and crankcase? I'm just hoping I can replace or correct the issue without having to dismantle the crankcase again.

Thanks
Sean

 

[Phototone]

Thanks again for all of the input. The mower runs great with some minor adjustments of the governor spring and I will be sure to order a tachometer to fine tune the RPMs. However, when running the mower, gas/oil mixture appears to be leaking from the crankcase. I believe it is dripping down the crankshaft and being spun off in a circular fashion. I replaced the upper and lower seals, but apparently my installation was inadequate (I'm not sure if it is possible to install the seals backwards or not). I set the seals in place with a piece of PVC pipe slid over the crankshaft and tapped with a hammer. Maybe oil was applied to the outer edge of the seal and prevented a good fit between the seal and crankcase? I'm just hoping I can replace or correct the issue without having to dismantle the crankcase again.

Thanks
Sean

It is possible to install the seals the wrong way. They will probably leak if you do that. The solid side of the seals should face out.

 

[Two-Stroke]

The engine will run better with a crankshaft seal installed properly. Any leakage in the crankcase saps power.

Another thought... I've never had a bad one but I guess it's possible that the seal is defective.

 

[bwright1818]

I had one that did the same thing.....it was noted to spin fuel/oil mix onto the concrete floor under it, while just trying to start it. A new seal stopped the leak and made it start better, too. There is a special seal puller for them but I was lucky...I had a self-propelled model; so I just took the gear box off and got the seal out that way. I did have to make a new gasket for the gear box. (This was an "F" engine. Not sure if yours is the same.)