View Full Version : 15.5 B&S hunts and backfires

05-30-2010, 11:19 AM
Hi all,
I have a Bobcat Walkbehind Classic with a 15.5 Briggs and Stratton. It runs great under light load, except it needs about 5 minutes to warm up before you try to cut at full throttle or it will bog down, then start to run rough and throttle-hunt. When there is a heavier load (taller grass) it will start to bog, the governor will kick in, and the engine will start to backfire while the governor hunts. I can see the throttle moving back and forth when this happens. It won't smooth out (even when load is gone) until I manually throttle down for a few seconds. I removed the carb and sprayed carb cleaner in all jets and passages.
What's up?

05-30-2010, 01:15 PM
How's that PCV rubber tube looking, if it's cracked or corroded it might need
replacing, whether it will fix the problem I could not tell you but I do know when
that tube leaks air it will make the engine run like crap.

05-30-2010, 01:17 PM
Sounds to me like a full carb rebuild is in order. This requires you to actually disassemble the carb and blow out the jets with compresses air. Don't try to blow it out still assembled or you'll damage the float. After the jets have been blown out let them and the rest of the carb minus the rubber parts soak in some carb cleaner overnight.
When's the last time you performed a tune-up such as air and fuel filter replacement?