Lawnboy lz21pnc

[bt3]

Van:

Nice mower! Glad you got it running.

Lawnboys are a piece of cake to work on once you know what you are doing and what the issues can be a a 2 stroke like this.

I am a synthetic 2 stroke oil fan. The #1 issue with Lawnboys is carbon buildup and ash in the exhaust ports and muffler. Your model has a muffler under the deck above the blade. You have to remove the blade, pop off the blade guide and then remove the muffler to clean it and check the exhaust ports. If they are dirty or clogged, pull the starter gently until the piston covers the ports. Use something wooden (not metal) like a dowel or a big pencil and clean the ports thoroughly. Blocked ports cause huge issues with power loss and bogging down. Also, clean the muffler. Youtube has a lot of advice on this. Just type in cleaning muffler on lawnboy and you will get a lot of videos. Some burn off the carbon, others just scrape it off with a putty knife.
This is why I converted to synthetic oil, and why I mix it at 40:1 instead of 32:1. You CAN safely lean out 2 stroke synthetic oil if you wish. I grew weary of cleaning the ports and muffler on F type engines, even when using LawnBoy oil. My oil of choice is Royal Purple 2 stroke synthetic oil. You can get it at any online company like Amazon or Jegs. But to each their own. Do what you want with your mower/oil.

You don't have traditional valves, you have Reeds or Reed Valves that you can see when you take off the carb. Sometimes these stick open or break an you have issues with starting and running. Check them whenever you pull the carb for cleaning or whenever the mower is hard to start or running rough.

The issue with power not adjusting via your throttle is most likely a bad connection on the carb. The throttle cable allows the governor vane to swing more freely to higher revs when you push it forward to power as this relieves tension on the governor spring. If someone goofed with it, it probably got misquied on the carb or broke off. You have to fix that. Another possibility is someone set the governor too high. You can adjust the vane with a thumbwheel just below the vane. If it's set too high, the throttle makes little or no difference. It just runs fast when started as the governor spring has not tension on it at all when set to a very high speed.

Another reason for bogging down and losing power is carb issues (set too lean or too rich) via the set screw. You can try 1/4 turns on the mixture screw and see if this helps. Also, there may be a issue with the governor vane being able to pivot freely. I spray carb cleaner on my thumbwheel area to make sure it swivels freely. Another issue for power loss can be leaking crank seals (top and bottom). The bottom usually fails first. If you see oil seeping out of the bottom of the engine crank, then you have a bad seal. These are not too hard to replace if that is the issue, but if they are leaking they do rob you of power.

Bad ignition modules can also mimic power loss. Sometimes a coil makes it hard to start or bogs down when under load, although if its running strong, I suspect more carb, crank seal, reed valve or mixture issues.

Take off the carb if you are comfy doing that and really clean it out. I am a fan of products like Seafoam. I run 4 oz of Seafoam in every 2 gallons of gas for stability and to clean out any junk or water droplets the carb may acquire. A dirty jet in the carb, or a bad float and needle will give you issues. These need to be checked. Make sure the plug is gaped correctly and is not soaking wet or carbon ashed up. This will tell you if it is running rich or lean. If you can do a compression test, you will find out if you have decent compression and that the machine is capable of good power.

Finally, an easy one, once you check to see if that throttle cable is engaging correctly on the carb, make SURE your governor is easily pivoting ad that it is set HIGH ENOUGH to cut without bogging down. I run mine between 3200 and 3500 rpm on full throttle.

Some ops report that even with everything perfect they still bog down in heavy or wet grass. Times like these call for removal of the mulch plate and side discharging. Also, you can cut on the highest cut height on the wheels. See if that helps. If you are bogging in normal dry cutting, then it's a power issue as above.

Good luck! Once you learn these machines, they are fun and simple to work on.

 

[Vanousb]

Van: Nice mower! Glad you got it running. Lawnboys are a piece of cake to work on once you know what you are doing and what the issues can be a a 2 stroke like this. I am a synthetic 2 stroke oil fan. The #1 issue with Lawnboys is carbon buildup and ash in the exhaust ports and muffler. Your model has a muffler under the deck above the blade. You have to remove the blade, pop off the blade guide and then remove the muffler to clean it and check the exhaust ports. If they are dirty or clogged, pull the starter gently until the piston covers the ports. Use something wooden (not metal) like a dowel or a big pencil and clean the ports thoroughly. Blocked ports cause huge issues with power loss and bogging down. Also, clean the muffler. Youtube has a lot of advice on this. Just type in cleaning muffler on lawnboy and you will get a lot of videos. Some burn off the carbon, others just scrape it off with a putty knife. This is why I converted to synthetic oil, and why I mix it at 40:1 instead of 32:1. You CAN safely lean out 2 stroke synthetic oil if you wish. I grew weary of cleaning the ports and muffler on F type engines, even when using LawnBoy oil. My oil of choice is Royal Purple 2 stroke synthetic oil. You can get it at any online company like Amazon or Jegs. But to each their own. Do what you want with your mower/oil. You don't have traditional valves, you have Reeds or Reed Valves that you can see when you take off the carb. Sometimes these stick open or break an you have issues with starting and running. Check them whenever you pull the carb for cleaning or whenever the mower is hard to start or running rough. The issue with power not adjusting via your throttle is most likely a bad connection on the carb. The throttle cable allows the governor vane to swing more freely to higher revs when you push it forward to power as this relieves tension on the governor spring. If someone goofed with it, it probably got misquied on the carb or broke off. You have to fix that. Another possibility is someone set the governor too high. You can adjust the vane with a thumbwheel just below the vane. If it's set too high, the throttle makes little or no difference. It just runs fast when started as the governor spring has not tension on it at all when set to a very high speed. Another reason for bogging down and losing power is carb issues (set too lean or too rich) via the set screw. You can try 1/4 turns on the mixture screw and see if this helps. Also, there may be a issue with the governor vane being able to pivot freely. I spray carb cleaner on my thumbwheel area to make sure it swivels freely. Another issue for power loss can be leaking crank seals (top and bottom). The bottom usually fails first. If you see oil seeping out of the bottom of the engine crank, then you have a bad seal. These are not too hard to replace if that is the issue, but if they are leaking they do rob you of power. Bad ignition modules can also mimic power loss. Sometimes a coil makes it hard to start or bogs down when under load, although if its running strong, I suspect more carb, crank seal, reed valve or mixture issues. Take off the carb if you are comfy doing that and really clean it out. I am a fan of products like Seafoam. I run 4 oz of Seafoam in every 2 gallons of gas for stability and to clean out any junk or water droplets the carb may acquire. A dirty jet in the carb, or a bad float and needle will give you issues. These need to be checked. Make sure the plug is gaped correctly and is not soaking wet or carbon ashed up. This will tell you if it is running rich or lean. If you can do a compression test, you will find out if you have decent compression and that the machine is capable of good power. Finally, an easy one, once you check to see if that throttle cable is engaging correctly on the carb, make SURE your governor is easily pivoting ad that it is set HIGH ENOUGH to cut without bogging down. I run mine between 3200 and 3500 rpm on full throttle. Some ops report that even with everything perfect they still bog down in heavy or wet grass. Times like these call for removal of the mulch plate and side discharging. Also, you can cut on the highest cut height on the wheels. See if that helps. If you are bogging in normal dry cutting, then it's a power issue as above. Good luck! Once you learn these machines, they are fun and simple to work on.

Wanted to say thanks for the info bt3. Gives me some great starting points to start to track down the issue. Not afraid to dig in. At 9.00 it's a great learning experience.

 

[bt3]

Typically, lack of throttle reaction is from a governor that is set too high or too low. I'm not 100 percent familiar with your model, but many have a spring on the governor that is attached to the throttle body of the carb. When you push the throttle open, it relaxes the spring and allows the governor to open more freely. If this is set too high (as an example), then it runs fast no matter what you do because the spring is too loose to have any effect on the governor from throttle manipulation.

Another possible issue is the pivot point of the wind vane governor assembly. Mine has been so dirty at times it could not swivel easily. A good dose of carb cleaner and then WD40 cured this.

You have to watch your mixture, even when you are working with Synthetic 2 stroke oil. You don't want to go too lean. IF you do, It is easy to trash the piston rings and then you have to pull the head to replace them from running too lean a mixture. Of course, time and hours on the engine contribute to this as well.. That's not a big deal to replace the rings, but it does take time. My mower was low on power from the day i bought it, and now needs a ring job. No question. Unfortunately, some issues with bogging down mean that you have too low compression. A bad reed can be a culpret, as can other issues, but the worst case is bad rings or other leaks in the compression chamber causing low compression and thus low power that can't stand up to high grass, wet grass, or other loads.

In another thread, I put my TOP TEN things to check on a LawnBoy. I'll see if I can find it and cut and paste it here for you.

Until I'm Dirt I will NEVER get a deal like you guys get. I paid $150 for my L21ZSM very used from a dealer 8 years ago. Here, you are lucky to get a a used whisk broom and pan for 10 bucks. Simply amazing the deals you guys get.

 

[bt3]

Here is that list:

1.) CDI Magneto bad, poorly gaped or a failing start or high speed side or both on the Mag, Spark plug dirty/gaped poorly or inoperative
2.) Exhaust ports/muffler clogged (2 stroke lawnboys do NOT tolerate clogged exhaust well)
3.) Carb issues. Clogged jets, mixture set improperly, float or needle valve issues. Make sure throttle is working, choke is closing and governor spring is relaxing on full throttle
4.) Reed Valves sticking or broken - take off carb and inspect them
5.) Crank seals leaking or worn out completely - gas/oil seeping out of the bottom crank is a sure sign
6.) Governor not set properly or not operating well. Set RPM around 3,200 RPM at high speed (F Engines). Make sure Governor Vane is swiveling well and freely and that the adjustment is working. Keep the swivel area clean and lightly oiled
7.) Poor compression issues that can come from some items listed above or from worn Piston rings
8.) Stale or bad gas, bad Gas/Oil mixture ratio, water in gas, contaminants in gas
9.) Clogged or dirty air filter - clean thoroughly and lightly oil
10.) Clogged Vent cap on gas tank filler cap, clogged fuel line, or fuel line shutoff valve

These are my top 10 issues that I suspect on my Lawnboy F-Engine. Of course there can be other deeper issues, but home mechanics can check these and make sure they are all up to snuff. Then if there is STILL issues, you call out the big guns or have a shop look at it.