warren@ihnss.UUCP (Warren Montgomery) (06/04/84)
(net.auto readers who are not mechanics can type 'n', sorry). My el cheapo Briggs & Stratton powered rotary mower has developed a familiar disease that I don't know how to cure. I have seen the same disease in other 4 cycle mowers over the years and never seen it really cured. Anybody know what to do for it? Here are the symptoms: 1) It's very fussy about starting. It starts best with the throttle just bearly open, and must be a allowed to chug along a while before opening it up. 2) It stalls very easily under load. Apparently, it has no torque with the throttle open at slow speed. This makes it unstable. Opening up the throttle can stall it, but backing off will re-start it if it's still spinning. Likewise, I can sometimes recover from a stall induced by heavy grass by backing out AND reducing the throttle. I have recently tuned it, including replacing and adjusting the points, adjusting the aramature gap, replacing the plug and adjusting the mixture screw to specs. (Though it is less unstable with a richer mixture, even though it idles much rougher and slower with this setting). All of this helped, but not much. I can't find any relevant information in the service manuals for this motor, but it must be a common problem. Any help would be appreciated. -- Warren Montgomery ihnss!warren IH x2494
wookie@alice.UUCP (Keith Bauer White Tiger Racing) (06/06/84)
Sounds like the poor thing is a little worn and probabky needs a valve job. I would first lap in the valves to see if that helps as this is a simple procedure on that engine. If that doesn't help the compression may be down and must be restored with new rings and maybe a bit of a honing job. I assume you have thoroughly checked out the carburetor for dirt/varnish buildup etc. It may also be that the carb is worn out allowing air to leak in around the throttle shaft or perhaps the idle jet is worn allowing to much fuel to flow at lower speeds. The carb certainly could be suspect as you say the mixture is richer at lower speeds. Let us know what you find! Keith Bauer White Tiger Racing
gmp@hjuxa.UUCP (PLEWA) (06/06/84)
The problem you appear to be having is a generic problem
with old "El Cheepo" Briggs & Stratton engines. There is either
a large amount of carbon buildup around the intake valve, which
tends to restrict the flow of carburated air from entering the
cylinder. This in its extreme, will even prevent the valve from
closing completely. The other cause way be just excessive wear
of the aluminum cylinder wall.
The determination of which is relatively simple. First
remove the spark plug and squirt a small amount of 30w motor
oil into the cylinder. Reinstall the spark plug (don't connect
the plug wire) and pull the starter cord. If the compression
(effort to pull the starter) has increased, than the problem
is excessive cylinder/piston ring wear. If the compression
remains the same then the problem is due to poor valve sealing.
(The oil only tends to increase ring to cylinder seal)
Excessive ring wear on this engine is cost in-effective
to repair. Valve seal or restriction on the other hand can be
repaired with out too much cost if you are willing to spend some
time.
The process consists of removing the head and valve tappet
cover. Removing the valves and scrapping off all carbon build-up.
The valve seats can be restored by "lapping" with lapping
compound, which is an abrasive powder in an oily paste. The paste
is applied to the seatting surface of the valve, and the valve is
inserted into the port from which is was removed. The valve is then
rotated back and forth 1/4 turn. This causes the mating surfaces to
be polished to a positive fit or seal. When this has been done to
both valves ALL traces of lapping compound should be cleaned from
both the valves and the block. Alot of damage will occur to the
remainder of the engine if this is not done. Reinstall the valves,
reinstall the head and tappet cover, and your problem should be
solved.ron@brl-vgr.ARPA (Ron Natalie <ron>) (06/07/84)
Air filter?
gt@hplvla.UUCP (06/09/84)
If you haven't tried it already, clean or replace the air filter.
George Tatge
HP Loveland Instrument Div.
ihnp4!hpfcla!hplvla!gtgt@hplvla.UUCP (06/10/84)
Nf-From: hplvla!gt Jun 12 10:56:00 1984 /***** hplvla:net.auto / brl-vgr!ron / 5:26 pm Jun 6, 1984*/ Air filter? /* ---------- */ Air filter: "a device usually used to filter air, hence the name."