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Lawn Boy 8290 and 5249

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evsnova74

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Discussion starter · #1 ·
I started working on this one today. I still don't know much about the model numbers or what is or isn't a good Lawn Boy yet, but as far as the ones I have my hands on this looks like it was the nicest one. 21", self propelled, all kinds of weird linkages up on that handle that I have no idea what all they do.

First off I checked for spark and that was good. When pulling the cord it really fights me so it seems like it has crazy good compression. So I moved onto the carb, it's a plastic one with the air vane throttle control. It didn't seem too bad on the inside so I just wiped it out and tried to roughly clean all the oily grass and dirt buildup on the outside of it. It's going to need a filter element because the one that came out of it was just crumbling.

When I put it back together and threw in some 32:1 it started leaking out of the little shutoff valve in the tank. Dripping when turned off, a small stream when turned on so that's gonna have to be dealt with. Oh and I also had to tighten the recoil another 360° so it would pull the cord all the way in. Here's the video of the first start:


Is that little valve serviceable?
 
#2 · (Edited)
Well it's running so that's a start. The shut off valve is serviceable with a new kit however you can try taking off the shroud, prying off the retaining clip, removing the shut off lever, washer and seal, and turn the seal over and reassemble. Those shut off seals can take a set over time and sometimes turning them over works. You can also try a couple other things. When all the parts are off the valve try shaving just a little off the 2 nubs that hold the seal. That in itself may allow the washer to compress a little more and stop the leak. The other thing to try is adding a second washer under the clip after shaving a little off the 2 nubs. This will definitely apply more compression to the seal. Barring all that, find the cheapest shutoff on eBay as the seals are all the same. Bill

If yours has the original carb the adjustment screw is on the top. Kind of hard to reach without a long wrench. I think it is 1/4 inch. Once you get the RPM's adjusted with the knurled wheel, (each click is 50 to 75 RPM), then you can dial in the carb with the adjusting screw.
 
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Discussion starter · #3 · (Edited)
It looks just like the Honda 16957-ZE1-812 which can be found for less than 10$, half of which is shipping. Kind of ridiculous because you could probably just slip it into an envelope and "ship" it for whatever the postal rate is right now.
Image
 
#4 · (Edited)
Well it looks "similar" but enough different that I don't think it would work. 4 holes are much bigger, and it's not smooth on both sides. Somehow I had it in my head that it had a center hole. I corrected my previous post. Bill
 
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Discussion starter · #6 ·
Well I may be getting some LB karma from all the trials and tribulations with the 5237 because the valve wasn't leaking at all. It was the new line that I cut too long not seating squarely.

And on top of that the 5249 isn't seized up after all, just a nest under the shroud (edit: scratch that, I didn't know this one had a brake. But it was for the better because it made me remove the shroud to check things out before pulling on it)
 
Discussion starter · #7 · (Edited)
I had a little problem with the engine on the 8290 wanting to die unless I feathered the blade engagement bail slowly. At first I suspected that there was a problem with the BBC or something but after learning how it worked, I tipped the mower back and held the bail down with my foot. The blade turned very smoothly and bounced back from the compression and all that. So I put my fears of something being wrong with that thing aside and started focusing on the carb settings.

First off I set up the optical tach and put one of the reflective stickers on the flywheel guard. 2400rpm on turtle and 3200rpm on rabbit so that was good to go. Then I started messing with the screw on top the carb, and that's when it started running worse than ever.

Turns out (no pun intended) I was treating it like a normal mixture screw but apparently it's just some kind of atmospheric equalization screw or something? If this is the right screw then I need to lightly seat it then go 5/8 to 3/4 turns out. This sound about right? Also what's with this "burble" I keep reading that it should have? Is that this thing where it sounds like these have a slight miss?
 
#8 ·
On that series of carb with the small hex screw on top that is actually an adjustable fuel flow needle valve, not an atmospheric adjustment. Pre set is two turns out from lightly seated. Turn needle valve in 1/8 turn at a time until it starts to falter. Then back off 1/8 turn at a time until smoothest running. Then back off an additional 1/8 to 1/4 turn for the perfect adjustment. Never adjust a 2 cycle to best lean running. And yes the "burble" is where is almost sounds rough but it's not. Bill
 
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Discussion starter · #9 ·
Ah ok, that's what I was trying to do but it didn't seem to be working very well. It's difficult to get the wrench under there with this thing smoking me out. You do this with it running or make an adjustment, start it, kill it, make an adjustment, start it, etc? Also I did try to tip it back to make adjustments and it seemed to want to die which seemed odd to me. Maybe the carb needs cleaned again.
 
Discussion starter · #11 ·
I tried some adjustments tonight but it was still smoking, and kept dying after running for 10 seconds or so so I couldn't even get it to warm up. Sure enough there was some stuff in the bottom of the float bowl. I'm going to attempt to add an inline filter tomorrow if I get home early enough and try to adjust it again.
 
#12 · (Edited)
I have heard that adding an inline filter when there is already one in the tank may restrict fuel flow. I wouldn't think the smoking would be due to lack of fuel. Sounds more like a bad float flooding out the engine. Just a guess. Try using the factory shut off to partially block the fuel flow and see if it smooths out and smokes less. Bill
 
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Discussion starter · #13 · (Edited)
I wasn't sure if there was a screen on these. I was just trying to prevent more crap from getting in the float bowl again, not attempting to fix the smoking.

Also for what it's worth the float looks good on this carb. I guess I could swap the new one out of the 5237. Or just swap the whole carb over from the 5249, that thing runs great though it smokes a lot in high speed. I'm afraid to adjust it or it might end up like this thing.
 
Discussion starter · #14 ·
It's too early in the morning to run this thing and try any adjustments, so I just wrapped up the carb clean out and got it installed.

And I know something like this would cause a lean condition whereas the smoking is likely a rich mixture, but I did notice that the mounting surface was warped.

Image


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I know I don't have that little lip anymore but it's gotta be sealing better than it was before just being flat now. And I made an effort not to over tighten the mounting screws too.
 
#15 ·
Yeah those tabs are notorious for warping. I would remove the tank, clean it out well, and see if you can see a screen over the outlet inside the tank and that it in place. FYI I have had floats that looked good but were not. Bill
 
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Discussion starter · #16 ·
I can't seem to get this thing to even run long enough to warm up and adjust the carb. Which is strange because it ran pretty good before, what changed? The only real change I can think of is that I started messing with the mixture screw. Maybe the coil is partially bad on this one too lol. Seems so familiar...

This is about the best I can get it to run:


Also removed the muffler just to check the ports and they were clean but wet. So maybe I need to keep focusing on the float.
 
#17 ·
Well to me that sounds like failing spark. Didn't notice a lot of smoke as it died. Does it re start right away? When it dies have you pulled the plug and checked for spark? Keep trying. You will get it. Bill
 
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Discussion starter · #19 ·
I have some strange findings to report. First off I swapped the coils on both of these, made sure they had good grounds and all connections were clean. Both mowers ran the same as before.

Then I figured why not swap the carbs too? That would rule out float, maybe not the tank but it should at least run long enough to burn through the fuel in the bowl. No change whatsoever. The 5249 runs perfectly and I still can't get the 8290 to run consistently without priming it every couple seconds.

What's left? Crank seals? Seems like that would cause a lean condition. Though the way I keep priming it could explain all the smoke. What else should I look at?

Edit: I just realized I never even examined the plug. Well it started raining hard so I'll look into that later.
 
Discussion starter · #20 ·
Here's another thing I didn't expect to happen. This morning there was what appeared to be oil on the front of the deck that must have dripped out of the carb. Of course I left the gas on yesterday but that's never happened before on either mower so I wasn't convinced that that's what it was.

Then I remembered that yesterday during all that priming at one point I noticed gas seeping from the primer bulb, all the way up at the zone control box. I guess it was sucking fuel up there? That seems like a float issue, as though the fuel level was getting high enough in there for the prime port to be able to suck fuel up. But anyway I think that primer line was just draining out overnight. I'll have to keep my eye on it because the float think could still be an issue.

Apart from that it was in fact the spark plug:
Image


After cleaning with a torch and wire brush it was good enough to see if it ran any better:
Image


And it did:


It smoked a little on startup of course, probably a lot of oil in the crankcase from before, but stopped after 5 or 10 seconds. Also kicked the blade on without wanting to die as much. So now I think I'm ready to dial in the carb mixture screw.
 
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evsnova74
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