Briggs black smoke and back fire
Hi, I need some input here! I have a 7 year old 13.5hp Briggs & Stratton vertical shaft I/C Intek OHV lawnmower engine that I have been tuning up over the past four weeks. There is one problem that is still bugging me. When I start the lawn mower, it gives a puff of black smoke then clears up. It also emits black smoke when I start the PTO blades. It runs ok at full throttle (not real smooth, but not too bad). At low idle, it sputters and backfires out the carb. It will occasionally stall at low idle.
Here is what I have changed or fixed in the past 4 weeks:
1. Changed the oil with HD-30. The oil level was below the good range, with some oil on stick, at start of season. Also the oil was pretty black and thin. The oil hadn't been changed in 2 seasons (lesson learned), but is now in the good range with new oil.
2. New air filter and also cleaned pre-filter with soap and water, then dried, and lightly oiled.
3. New spark plug (gap 0.030 in). Old plug was somewhat black but not oily
4. Drained old gas, blew out plastic gas tank with compressed air, changed fuel filter and added fresh gas.
5. Removed carburetor. Removed mix screw/spring, idle screw/spring, fuel solenoid, bowl, float, needle, main jet, and the brass nozzle that goes up the center. I soaked all the small metal parts in carb cleaner (except needle). I shook the float to make sure it wasn't leaking. I wiped down the needle with a tiny bit of carb cleaner ( I did not soak it because it has a rubber tip, which looked ok). I sprayed carb cleaner into all holes of carb, then I used compressed air to blow off carb and in holes, and also all the small parts. The mix screw I adjusted out 1 1/2 turns. The idle screw I adjusted out 5 turns. After putting the needle and float back on, I turned the carb upside down to make sure the float was about level. I also blew into the fuel inlet to make sure no air would pass. If I lifted the float then air would escape. I also hooked up the fuel solenoid to 12V to make sure the plunger pulled in when powered up (it worked fine).
6. Since it was running rich and the float/needle seemed ok, I decided to check the flywheel key to see if it had sheared causing it to be out of timing. I pulled the cover/screen then removed the flywheel nut. The key was perfectly in tact and lined up beautifully with the notch on the crankshaft. Damn I was really hoping this was the problem after all this time!
7. Adjusted valve clearance (this fixed my hard starting problem). Thanks Walt Conner!
At this point, I focused on the magneto. I removed it. I sanded the two contact points with 600 grit sandpaper until there was only very little rust left. I also checked the flywheel magnet with a screwdriver and lightly sanded it. Can rust here make a difference? Also when I pulled the spark plug boot off tonight, the metal piece that is crimped onto the wire stayed on the spark plug! I pushed the wire back in. It still ran the same (black smoke, back fire, hesitates on slow idle)
Well, I just wanted to mention a few things before I go. These may or may not have lead to the problem I'm having now:
- Oil was changed very infrequently (every few years)
- Left the mower outside (uncovered) for approximately half a season (lesson learned)
- Always use water to spray grass off deck and engine, after engine is cooled. Also spray water to clean flywheel screen
- Always mow grass on sides of sandmound (steep incline). Whenever I would mow with carb side down, it would smoke (blue), then when I would get on level land, it would stop smoking
- one year I had a problem with a belt (now fixed). I would have to start the the mower with the PTO blades on
- didn't adjust the valve clearance until this year, which caused hard starting and two fried solenoids.
The Briggs engine is:
Type 0117 E1
Any help or input would be appreciated! Maybe I overlooked something or did not do something correct.