Briggs 21 HP barley runs , no power.

[partsman430]

I have a Troy Built mower with a Briggs 21HP engine. It's 15 years old never had a problem and ran great last week. My wife says she has heard a ticking sound for a few weeks, but I haven't. Today it wouldn't start, I found a mouse nest under the shroud, I cleaned it out now it starts but runs bad, idles up and down , pops up through the carb and has no power, sounds like timing to me but I don't know how a mouse nest could cause this. Should I remove the flywheel and check the key or look for something else? Any ideas would be appreciated.

 

[Pumper54]

Critters like to chew on stuff, look to see if they might have chewed on some wires or fuel lines, air filter ect.

Tom

 

[partsman430]

Thanks Tom.

 

[motoman]

Rodent could just be a coincidence and something else is acting up. On the other hand the nests are often mentioned as a source of overheat which could kill a spark coil, but perhaps not the misfiring. I have an intek 24 and can get some idea about flywheel slippage if I look at the leading edge of the flywheel magnet as it passes the coil. Just as it reaches the coil on compression the piston sb at TDC. But this is not precise unless you have marked TDC and probably no good if you use the 1/4" rule. Or you could try a timing lite, but again , need an accurate mark. Some remove the big flywheel nut and look down into the keyway and are able to see if the key is damaged. I have never tried that.

 

[Tinkerer200]

As said, mouse nests often lead to overheating which in turn results in valve guides moving which interferes with valve operation. I would look under the valve cover and see if all is well there. Valve guide should not extend more than 1/8" above the head casting.

By the way, posting engine model number is helpful when asking an engine question as there are multiple 21 hp B&S engines.

Walt Conner

 

[partsman430]

Thanks for the ideas, I do think it's something internal.

 

[motoman]

Partsman, Moving guide and associated problems ARE internal. Pushed guide will not allow full lift of valve , eventually reducing incoming charge insufficient to fire. Try comparing the rocker movements with a steel rule , or better, a dial indicator if you have one. The guidelines of the pros in this forum is that a 15 year run is a good one for lower end AC units (no offense here). My Intek 24 was pampered and is now down 1 cyl after medium use run of 12 years. IMO

 

[partsman430]

Partsman, Moving guide and associated problems ARE internal. Pushed guide will not allow full lift of valve , eventually reducing incoming charge insufficient to fire. Try comparing the rocker movements with a steel rule , or better, a dial indicator if you have one. The guidelines of the pros in this forum is that a 15 year run is a good one for lower end AC units (no offense here). My Intek 24 was pampered and is now down 1 cyl after medium use run of 12 years. IMO

Thanks motoman, I think you're right, I'll let you know what I find.

 

[partsman430]

Motoman you were right. 2 Valve guides had moved partially out, bent 2 push rods. Replaced, repaired and it runs great. Thanks for the info.

 

[Tinkerer200]

I think I was the one who suggested valve guide might have moved, If you simply pushed them back, they will not stay, there are other things you need to doto prevent reoccurance.

Walt Conner