Briggs/Stratton 4 hp Quatro

Briggs/Stratton 4 hp Quatro
On an MTD 21 " mower, maybe 8 years old.
For several years, even right after disassembling/cleaning air filter, carb, changing oil, etc etc, it'll start up and run steady for about 10 seconds, then it revs up and down (almost killing) in an endless cycle. About 30% of similar B&S mowers I see running in the 'hood do the same thing. Oh, and, of course, it fouls spark plugs.
I cleaned it up last fall. Start it up this spring, does the same thing, but, after reaching minimum rpm, it clanks while trying to rev up again. Sounds like serious pre-ignition or even a flogging rod knocking. Motor has had no hard use: I mow my little lawn at an idle.
Anybody got a handle on such behavior? Smokes a little only when first started. Compression feels OK.
Cheers, Puddin'
"Life is nothing but a competition to be the criminal rather than the victim." - Bertrand Russell
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Puddin' Man wrote:

Flywheel key is sheared.
Rob
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

I dunno they even gotta flywheel, proper. Suspect the blade weight provides much of the inertia. IIRC, there's no key on the bottom end of the shaft.
But, I move the blade back/forth whilst holding the Finned Aluminum Monstrosity on top, and feel a little play.
Can't remove the FAM 'cause it's held by a 1.xx" nut in a recess for which I have no socket (sigh).
"Gawd, I hate B&S small engines!"
Wonder if the little Honda OHV's have priced down reasonable? May find out soon.
Cheers, Puddin'
"Life is nothing but a competition to be the criminal rather than the victim." - Bertrand Russell
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Puddin' Man wrote:

Your "FAM" is the flywheel. It's weighted & balanced, & contains magnets for the magneto ignition, as well as fins to move air over the engine for cooling. It is keyed to the crankshaft.
Evem if you get the nut off, you will still need a puller.
Rob
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

I kinda figgered ...

Approximate weight of blade assy? Approximate weight of FAM? Maybe it's "half a flywheel"? :-)

OK ...

Thanks. I guess I'll start by pricing the Honda's.
Tecumseh's are no less a PITA?
P
"Life is nothing but a competition to be the criminal rather than the victim." - Bertrand Russell
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
The Honda is prone to the exact same problems.
You either need to buy, own, and learn to use the tools to deal with a lawn mower engine, or you hire someone else to do it for you, or you buy a new lawnmower as necessary. Simple choices.
Honda engines are very well made and would be my engine of choice, but they also need attention.
--
______________________________
Keep the whole world singing . . . .
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Having had a Honda (not a mower) in the garage these last 19 years:
"I Believe Every Word You Say!" :-)
Puddin'
"Life is nothing but a competition to be the criminal rather than the victim." - Bertrand Russell
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Puddin' Man wrote:

Well, I have not had a Briggs failure(of my own, anyway), & the only thing I've had to repair on my Tecumseh's are the flywheel key(my fault) and a head gasket. I can do both of these jobs in a few minutes blindfolded.
The Briggs failure was my cousin's 6.0. Ran it low on oil & threw a rod(but not through the case).
I ordered a new piston, rod, & gaskets, & put it back together about 5 years ago with the advice to watch the oil, & use synthetic. It's still running strong. Unfortunately, the oil never gets changed.
If you want to do these simple repairs, you need to have the right tools & knowledge.
Rob

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Absolutely! :-)

Is true, is true. Mea Culpa!
Only thing is, it hasn't run properly for years, and:

And there's no mixture adjust on the "carb", etc etc.
And when I post a query -here- as to why it fouls plugs, revs up and down, etc, I get 100 zillion blank stares. :-)
So, question becomes, how much do I wanna invest in tools, etc to repair/maintain my B&S? Prevalent evidence indicates they (say, 3.5-6 hp, enyway) were designed as throw-aways.
Thx, Puddin'
"Life is nothing but a competition to be the criminal rather than the victim." - Bertrand Russell
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.