There are several Deere 125 models. What does your owner's manual say about fuel usage? But I'm going to go out on a limb here and say if you changed spark plugs in this- it is a gasoline engine. . . Black smoke is typically a rich condition. Check the oil level . If it stays consistently full and the level doesn't seem to rise, that is a good thing. Check the air filter for being excessively dirty. Black smoke as it is first started for a matter of seconds is considered normal.

Had this issue: 1:Changed the filter . did not work properly 2: removed the hose and blew into the gas tank , same issues, run and die. 3: rmoved the hose from carb and blew with hose this helped ,till changes gas.. it ran for like 10 minutes. 4: my gas cap did not have any air holes, so i just did not tightened al the way down...ran till i finished it takes a good hour to cut the grass... Thank you Herb

I believe the best buy you will get for the parts to service the JD tractor is the one from the John Deere dealer. JD has a service package that contains the oil filter, air filter and foam sleeve, 2 qt of oil, spark plug, and gas filter. Last year it was about $40, about $35 with coupon. For several years I have checked the individual prices at the big box stores and others. I never could find a better price than the JD dealers. Buying the service kit from JD removes the part search and what is best for the tractor. The JD dealer asked you what tractor you have, looks it up in the computer and hands you the box with the recommended parts. could not be simpler that that You can remove the deck, grease the fittings, check the belts, sharpen the blades, and install the new parts on a Saturday morning. You can use your manual as a guide. If any of your belts are cracking or splitting now is a good time to replace them . This post was edited by knuttle on Mon, Nov 18, 13 at 16:27

Similar problems are becoming common on Vanguards. Here are a couple of ideas. 1. sometimes the Mikuni fuel pump starts to seep fuel into the crankcase (from the vacuum line). Fuel fumes in the crankcase are expelled into the air filter compartment from the breather and ingested through the carburetor air stream. This results in a rich fuel air mixture. Remove the air filter and disconnect the breather hose from the air filter housing. flex the breather hose so it is facing away from the carburetor inlet. Run the engine to see if there is a change. 2. Where did that engine oil go? If oil fumes were expelled from the breather, perhaps the air filter received a coating. How could this happen? I don't know -maybe by excess tipping? If the air filter is contaminated, a rich mixture might occur. Sometimes the wrong filters have caused this type of problem. Aftermarket filters have also caused problems because they are manufactured with more restrictive paper. 3. sparkplugs that are the wrong heat range or sparkplugs that are misfiring may allow black exhaust to be expelled. Sometimes the mis fire may not occur until the engine gets real hot. The experts may have more suggestions if these ideas do not help.