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The engine is a 21 HP, B&S Platinum with XRD engine family ABSXS.5402VB. Model 917.28922 on the manual cover or Model 917.289223 under the seat (YTS 3000). Blowing black smoke from the muffler when you start it up and when you put a load on the engine such as engaging the mower and at times when mowing the grass it throws out black smoke. Also has a smell but not sure what it is. When I took the plug out it is black with soot on it. Today I put a new air filter, oil and filter, fuel filter, spark plug. I also took the carb bowl off to see if it was gunked up but it looked good no varnish the gas in the bowl was clean the float was moving. After completing the above started it up no black smoke but after a few minutes back to black smoke. Even though it smokes the lawn tractor runs, it sputters every now and then but was able cut the grass and it idles although a little rough. The mower is three years old. Haven稚 worked on Lawn tractors but have rebuilt my rancher carb and triple mikuni's on my jet skis. Any suggestions are appreciated. Thanks.

From your description your engine is running way to rich. First thing to check, is to make sure the chock is opening fully and staying open. Second thing is to see if the float level is to high.

Thank you sir. Here is what I tried today. Removed the housing so I could see if the choke was opening and closing. Choke was moving and working as I moved the throttle/choke control up and down. It also works fine when the engine is running. Not sure how to adjust the float. Here is what I did. Removed the bowl, when the float dropped down gas was flowing when I pushed up on it with my finger it shut off. Checked the float needle and the rubber tip looked good and spring was working. Took the float off and shook it to make sure it wasn稚 cracked and there was no gas inside. I took the carb off and blew air through all the openings, everything looks nice and clean. Put a new plug in and it idled great but after 5 minutes it started to smoke as I was mowing the grass. Pulled the plug after 15 mins and it was black and started to get soot on it. So I noticed what looked to be like two adjustment screws on the carb. One screw was on top of the carb with a screw and spring and the other was off to the side with a screw, spring and black cover I believe it痴 a cap limiter? Should I try adjusting these screws? If so, which one or both. I also did a compression test 3 times and each time it was 104, 105, 105. Not sure what the compression should be. Thanks.

If I came into the shop I would go after the carb, as I feel this is the cause of the problem. Could you please find and post all the numbers on the engine. It is stamped on the shroud. From there I can look up the parts you would need and give you instructions to follow. I will try to get back to you as soon as I can, but right now I'm working 9 hour days and don't sways have time to check the forum.

These were the numbers I found. Also the black on the plug is more of a wet looking than dry. I took a picture and when one of the kids come home I will have them help me download it.
Model 1331877
Type 1371 B1
Code 100608ZD
Serial 10 0608 ZD 46847
Engine family ABSXS.5402VB 279223
EU: e11*97/68SA*2004/26*0392*03
Displacement 540cc ECS: EM

Thanks.

Please check that model number, it should only have 6 digits.

Yep I mistaken wrote down the number 1 for L on my paper.
Model is 331877.
pulled the valve cover today going to check the gap since this is also a little hard to start. Can also see where on one of the bottom bolts must of leaked a little as there is a collection of dust around it. This cover doesnt have a gasket looks like silicone. I used threebond silicone liquid gasket 1211 on my jet ski exhaust. Any chance this will work on this cover or is there another product I should use. Reading I see different gap settings. Intake .006, exhaust .008, both at .004 any suggestions? also which one is the exhaust and intake? I noticed the rods are different material. I dont see any leaks around the head gasket. Thanks.

Here is a service manual which may help you out. The valve clearances for you engine are .003-.005 for both valves, which means your valves are set correctly.

http://dl.dropboxusercontent.com/u/12502267/B&S Service Manuals/10_276781SingleCylinderOHV.pdf

I would do a good carb cleaning and rebuild of the carb, your's is not the easiest and if you don't feel comfortable take it to a good shop. If I did my research right the rebuild kit number is 796184. Take your model, type and code numbers to the shop and have them double check so you get the correct one. Along with the manual procedure on rebuilding, here is what I do.

Needle and seat replacement

Remove the carb, and then remove the float bowl. Check the float bowl jet (which is the bowl screw) and make sure the jets both horizontal and vertical are clean and open. Tip the carb upside down and remove the float pin and float with needle attached. Look in the float needle passage and you should see the red float seat at the bottom of the passage. This is where a #5 crotchet hook would come in handy as you need to remove this seat. If you have no hook, but compressed air, you can blow through the fuel inlet and try to pop the seat out. Put your thumb over the passage to prevent the seat from flying who knows where. No air or hook try bending a stiff paper clip to dig the seat out.

I would either give the carb a good 24 hour soaking or have it ultrasonically cleaned at this time.

With the seat out clean the passage way with carb cleaner. Now you must find a drill bit slightly smaller than the passage way, to be used to press in the new seat. Apply a very, very small amount of a very light lube to the new seat. 3-1 oil or lighter, to help seat it better. Carefully insert the new seat in the passage way with the rings on the seat down toward the carb body. Slowly and carefully force the seat down with the back end of the drill bit. Once it is seated, check to see that it did not flip and the rings are up. *Next check to make sure that the float does not have any liquid in it. *If it does, replace. *If everything looks correct, attach the new needle to the float and install with the float pin centered. It everything is correct, the float should seat level to the carb body, when looking at it upside down. If everything looks good reattach the float bowl, making sure that both the bowl gasket and the nut gasket seal properly. Reinstall on the engine and test unit. Remember to have patience and take your time. Good luck, but I don't think you'll need it.

PS: *On the side of some Tecumseh carbs you will find a plastic cover. *Under this cover will be an idle jet. *Remove it and check to see that the jet is open both horizontally and vertically. *You should be able to push the old float needle wire through the vertical opening.

Re: 21 HP B&S Black smoke from muffler, possible Carb adjustment (added pictures)?

So while waiting to order the carb kit I decided to check the head gasket hopefully pictures worked. Looks like a lot of build up, should I wire brush this off, take it somewhere to have it cleaned or leave it alone. Is this the result of the bad carb? is it major problems? There were no cracks on the head gasket. Took a picture of the outside of the engine looks like build up around the breather tube.

You and others may tell me I'm nuts, but I don't see anything to be concerned about. I would take a soft brass wire brush and clean the piston head and cylinder head a little. Don't get carried away, no need to get it spick&span. Clean the gasket mounting surface real good. Dirt around the breather tube is all normal, I have no concerns there either. Get a new head gasket, don't try to reuse the old one, it won't work.

Thank you Sir. I need to order the carb kit and follow your directions for a rebuild. Most likley wont get to it until next week got a lot going on for the rest of the week. I appreciate your detailed instructions and the time you took out of your day. I''ll be sure to follow up once complete.

Finally got to work on the lawn tractor today. Rebuilt and cleaned the carb per guidance, adjusted the valves and put the new head gasket on. Ran it for about 10 minutes and so far no black smoke (little puff only on start up). Figured I would check the plug and it was burning normal no black carbon at all after 10 minutes. BUT while pulling the boot off the plug, to get the plug out the metal connector on the spark plug wire pulled off the wire and was stuck on the plug. How do I fix this? Do you bend the wires back against the insulation then clamp the metal piece around it?

Re: Update 21 HP B&S Black smoke from muffler, possible Carb adjustment?

Update. Finally got it running right for 3 weeks now. Ended up taking the carb off soaking and rebuilding it and draining the old gas. Also readjusted the lifters (slightly out of specs) and put a head gasket on it (although there was nothing wrong with it). I feel rebuilding the carb did the trick. Special thanks to Rivets for the instructions and suggestions. Thanks again for saving me a few bucks.

I need the torq. specs for the head bolts on this engine if anyone has them.

Model 331877
Type 2371G5

Should be able to find everything you need in this manual.

https://docs.google.com/open?id=0B6NaqjIxWV1ybEN0LWo3azl6OUU

I have one of those engines on my JD and it's the worst engine I ever owned. No black exhaust visible, sometimes blue at start up, but the plugs have been black from the beginning since shortly after the tractor was new. The strange thing is it drinks gas, but even after it is warmed, after being off for 30 minutes it has to be choked to start.

Thanks a bunch for the link. It helped a lot with the torque and a few other things I had questions on.

SeniorCitizen said:

I have one of those engines on my JD and it's the worst engine I ever owned. No black exhaust visible, sometimes blue at start up, but the plugs have been black from the beginning since shortly after the tractor was new. The strange thing is it drinks gas, but even after it is warmed, after being off for 30 minutes it has to be choked to start.

Click to expand...

My problem was a blown head gasket that was making the engine burn oil and puff out white smoke. I've been told this is a common problem with this engine.

This engine is on a Craftsman riding lawnmower and does really well on gas and usually doesn't need to be choked at all, except in the winter. Along with cutting grass it has to pull "mule" duty all year long too.

I believe that a little puff of black/blue smoke at start up, shut down, and engaging the load is normal for OHV engines, this one does it, but don't take my word for that.