I found the message I pasted below on this group a few days ago. I had
this exact same problem with the same motor (10A902) 4HP. after
reading all the replies I went and replaced the diaphragm. The mower
now has a steady idle but it is much much higher than it was before.
The mower also seems to run twice as loud as it used to. What do I do
to fix this problem.
My briggs and Strattan mover was working fine up until I ran it dry
using every drop of gas. The next time I used the mover it runs
with RPM's going up and down but never stalling.
Is there a block in the carberator from the garbage at the bottom of
tank ? Do I have to take it apart and clean ?
Any help would be appreciated !!
If he didn't change the screw before or after replacing the diaphragm, that's
probably not the cause of a much-higher idle.
You might have a vacuum leak, where air is getting sucked into the engine
around the gaskets. Make sure the gaskets are all seating properly and the
screws are tightened correctly. "Real tight" isn't as important as tightening
evenly the several screws that hold a diaphragm or gasket.
On Tue, 31 Jul 2007 06:45:02 -0700, firstname.lastname@example.org wrote:
As far as I know, no Briggs and Stratton 4HP made in the last decade
or so has a carb with an idle adjustment screw. They use that
el-cheapo and funky vacu-jet carb with the vibrating diaphragm that
acts a a fuel pump. There is neither an idle adjustment or speed
screw. These carbs also have no float or float level adjustment.
In effect, the fuel tank IS the carburetor bowl.
Did you replace the external throttle springs correctly? Those engines
run at a more or less fixed speed determined by the back spring
pressure on the governor linkage. Some mowers have a "throttle"
adjustment, either with a lever or a cable, that simply changes the
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