STRANGE CARBS AND CAMS
This past summer,I ran across some interesting things
concerning carbs and cams in Briggs an Stratton
engines.
First of all a customer brought a riding mower in with a
12 hp Engine the complaint was that it was running wide
open whenever it was fired up.I immediately checked all
of the linkages going to the carb,governor linkages and
so forth.They checked out fine
and if I had not seen this before, I would have been
stumped.
What had happened and apparently was a defect that
Briggs was having on some of these engines.The
screws that hold the butterfly in the carburetor in place
had vibrated out and were sucked into the engine,
passed the valves, into the head and either they will
imbede themselves into the soft aluminum head or
piston, or pass out the exhaust side.AT either rate the
engine runs wide open because the butterfly cannot
control the gas flow .I had one that had sucked the
butterfly into the manifold, intake manifold.I have saw
this happen to several 12 and 14 hp engines, so I know it
has to be a defect of not putting enough loctite on the
butterfly screws
Secondly, a customer brought a 15 hp intek, Briggs an
stratton in.The symptoms were,it would fire up and run
on idle, but would not idle up.I checked the carb, and
immediately after finding it to be o.k. Proceeded to
adjust the valves,being a overhead valve engine. That
done, the symptoms were no better.What was
happening was the intake valve was letting fuel in, but
the exhaust valve was not staying open long enough to
let exhaust out,so Iput exhaust valve way out of
tolerances to see what would happen, no
change.Immediately the possibility of a bad cam came
into mind,but the engine was no more than two years
old, then I saw made or assembled in Mexico on the
flywheel cap.I pulled the engine, disassembled the
bottom crankcase, pulled the cam and wala, one of the
lobes was almost completely gone.The exhaust lobe to
be exact. I did this to two 15 hp inteks last season,so
apparently there is a defect in some of the cams in the
newer engines,possibly its been solved by now.Also did
this on a 17 hp engine.Note; the replacement cams were
of much better quality.
Hope these snippets of info will help you,if you run
across these type of things in the future.
