jdcherry

I have a Huskee 22HP Briggs&Stratton riding mower that is 3 years old with about 92 working hours on it. When you start up it sounds like little explosions going off in the engene. It sounds like it could be missfiring. when you decrease the throttle, it backfires at the engene, but not very loud. I cleaned & regapped the pluggs and cleaned the air filter. No help! I have always had to turn the starter over many times before it cranks even when new. After it cranked it always ran smooth as a kitten. Could it be trash in the carb? Or one of those square black boxes on the font side of the engene? Any advice welcome!

Thanks JDC

coleman mobile

Is it smoking or any fluids (like gas or water) coming out of the muffler?

Volt-Schwibe

Based on what you're describing, it sounds almost as if there's a burnt valve, or that the valve timing is off. Really rich fuel mixture can sometimes cause the backfiring like you're mentioning too though. On a lot of these small engines, even though it's a 4 cycle engine, the spark plug fires once per full rotation. What this can mean is that if there's too much unburned fuel in the exhaust, or if the intake is too hot, then it can touch off when the spark plug fires the second time. This also depends on the timing of the spark being right. This could even be due to a partly sheared flywheel key, but on something that low-hours, i doubt that it is.

To check the timing, you'd need to somehow see the positions of the valves, according to the crankshaft, while also noting the location of the magnet on the flywheel.

At about 5 btdc, (you can get a book at the library that will have the exact numbers) the magnet should be just about to pass the coil, if that's normal then check the valve timing, the intake valve should be 100% closed before the piston starts it's upward swing for compression, and then the exhaust should open more or less exactly at the bottom of the exhaust cycle.

If it used to run smooth, then this probably isn't the internal timing gear being wrong, as it's usually never something that fails. What is more likely here is that it's the ignition timing, or the fuel mixture.

I can't say exactly what the setting is for your low-rpm fuel screw, but i always set my own by screwing it in all the way, (keep track of how far you turned it, so you can turn it back in the worst case) and then unscrewing it about 1 whole turn. Then i start the machine up, and i aim for that special spot. (you can sorta hear where it runs nice and smooth with a high rpm, and then just barely turning it makes it start to get choppy) Then i make sure it still revs smooth without sputtering when i goose it.

I'm not sure all of that helped, but maybe.

jdcherry

Thanks for the suggestions. After I cleaned and regapped the pluggs it ran perfect while I mowed my yard. When I cranked it up 3 days later it was misfireing and running ragged again. Also, I ran it out of gas right before it originally began this problem, making me think trash in the bottom of the tank may have entered the carb or fuel filter. I think it might be wise to change the plugs and fuel filter before getting into the more complicated task of cleaning the carb. Does that seem worh doing?

Volt-Schwibe

Changing plugs and fuel filter is a maintainance thing, so if it hasn't been done for awhile then it's never a waste of time. And, it's always best to start with the easiest stuff first.