If the muffler is bad, your lawnmower is going to be REALLY loud. A muffler itself can not cause smoke, because all it does is muffle sound. Imagine a maze made of walls, that's what's inside a muffler. As sound bounces off each wall it gets quieter and quieter, thus muffling the sound. It does not trap engine smoke, because a healthy engine doesn't smoke. First, I would make sure your oil cap and drain plug are tight. (You may find your problem here) Don't want water getting in there in Step 2. Second, I would clean the entire engine area really good with some engine degreaser(local auto parts store) and high pressure water(regular hose is fine with a high pressure nozzle). Just spray it on, wait a few minutes, then rinse it off. Make sure the engine is cool before doing this. You may have to scrub any tough spots. Also avoid spraying directly at the air filter. After that, just wait and see if you notice any fresh oil dripping on/around the muffler. Hope this helps! This post was edited by ENVY23 on Mon, Apr 7, 14 at 18:18

3.75 Briggs carb rebuild This is an easy DIY job to replace the diaphragm of the carburetor. A damaged diaphragm will cause engine surging, hard starting, and erratic high speed operation. You may also notice that the primer bulb isnt working properly. This is an overview of the carburetor and these types of carb-over-tank are typical of small Briggs engines. Note the two governor springs. The carb/tank assembly is held in place by a ½" bolt to the left of the carb and a 3/8" bolt on the engine head to the right. Remove both bolts and pull the tank straight out with a rocking motion. If possible, the carb/tank assembly should be blown off with compressed air and all loose dirt removed. Use the proper safety equipment, especially safety glasses, before using any compressed air in any of the steps below. In the highlighted area you will see the governor linkage still in the throttle plate of the carburetor. You will have to gently separate the carb/tank assembly from the linkage. It is a Z type linkage. It is not necessary to remove the springs or the other end of the linkage, from the governor. Note that on the rear of the carburetor is found a white plastic ring and O ring. Sometimes these remain on the tube of the engine housing. If so, place them back into the carburetor body, as shown, before reinstalling the carb/tank to the engine. Note the raised area of the diaphragm. This is caused by age, but more often, by ethanol fuels, which damage the diaphragms. A damaged diaphragm will cause engine surging, hard starting, and erratic high speed operation. You may also notice that the primer bulb isnÂt working properly. Shown here are the dip tube, which brings up gas from the tank, in the bottom left corner. Just behind that and partially obscured, is the orifice that compressed air can be used to clear the dip tube of debris. It also leads to the primer bulb, so any air must be low pressure and the primer bulb must be held in the depressed position to prevent it from blowing out. In the center top, youÂll notice the jet, surrounded by a wire mesh filter. In the bottom right is a spring. Be careful to not lose the spring or forget to install it during reassembly. Remove the old gasket and diaphragm combo from the carb body. Install a new gasket/diaphragm on the smooth surface of the tank. I always blow out the tank with compressed air to remove dirt and any water. Be aware that there may also be old gas in the tank. I always empty the tank and let it sit in the sun until all the gasoline evaporates before applying compressed air. Align the carb and lower it down on top of the gasket, trying to keep the five screw holes in the gaskets aligned. Insert the screws and partially tighten them and install all five screws. Tighten each screw until it gently bottoms out. Then turn each screw another quarter turn. It is not necessary to use more than a few inch pounds of torque on these screws. Reinstall in reverse order. When installing, be sure to engage the breather tube with the rubber piece on the carburetor.

I bought one and it has run great, the only time it sputters is when the cutting line is getting short. I tap the head get more line to feed out and the sputter is gone. My spec sheet calls for 20w-50 oil. My experiance with most chinese made gas motors (which is probably most that we find available these days) is that they test run them at the factories then ship them leaving some gas in the fuel system, and since from test run, shipping, to sale is usually several months this allows the fuel system and residual gas in it to lacquer up. On anew purchase I usually put some rubbing alchohol in the fuel tank, then take the spark plug out, prime the fuel system, pull the start cord till I smell rubbing alchohol coming out of the spark plug hole. Then I let it sit a day so, the rubbing alchohol dissolves the lacquer, then I put gas in and start it up. I never have problems using this procedure. If you have lacquer gumming up your jets you can adjust the carb all you want but it will never run right!!

First off you can check for spark by removing the spark plug, plug it back in and lay it onto the metal part of the cylinder jug. Pull the rope and you should see nice blue spark arching. Now what kind of switch do you have? Does you switch just shut the engine off or do you have two positions on it ON? or OFF?.(you have two wires going to the switch, with the two wires touching it should cut the ignition off and with the two wires seperated you should get ignition, if so the switch is bad?) First thing I would suspect with no spark at the plug would be the cheap switch? You can remove the switch and check it with a mulimeter. it should show conitunity in the off postion cause this it what shut the ignition off by grounding out the coil. I have the one position switch and my problem was the weed eater would not shut off. The cheap switch would not ground out the coil so I search through my spare parts off junked weedeaters and found a good switch. I dought your weedeater has points, IMO they started using electronic ignition about 20 years ago?