As Stormin suggested I agree you should check the "air gap" on the ignition
coil even though it sounds like a fuel problem. I remove the ignition coil
every few years and clean the edges and magnet on the flywheel with
sandpaper and coat it with a little oil or vaseline or whatever. This helps
keep down the rust. I generally use three thicknesses of printer paper to
adjust the air gap. Check the spark plug connector and clean out any
corrosion and squeeze it a bit with pliers to ensure good contact.
Sometimes the spring for the governor will get a bit stretched and can be
shortened to where it just barely has tension with the engine off. Try
holding the throttle all the way closed while it's running and adjust the
idle speed to where it seems about right. If it's too low it may be hard to
start. Also, if the throttle/choke cable has slipped it can cause the choke
to be on or off when you want it the other way. Removing the head might be
in order to--scrape off the carbon deposits and clean the valve seats being
careful not do damage the seats. I have had success many times simply by
putting some high-temp silicone on the old head gasket and reusing it.
My old B&S lawnmower sounds very similar to yours but it's only 23 years
old. My experience with these engines is that as long as the piston is
still attached to the crankshaft they can be made to mow lawns. I was
having a lot of trouble with mine in the past with hard starting and I even
turned the engine sideways so I could pull the rope from the side. This
arrangement also eliminated some problems with the cable moving out of
adjustment as it eliminated the 90 degree turn in the cable. Also, check to
be sure the blade is tight. These things need it to maintain momentum.
I've worked on a lot of standby generators with small
engines and one of the problems with older engines
that have accumulated a lot of hours is valve seat wear.
The valve recedes into the head decreasing clearance
at the end of the valve stem. You can actually heat up
such an engine with a propane torch and the expansion
of the metal parts will allow it to start easily. If you
can adjust the valve clearance, I do believe your engine
will start easily again.
Try this: it won't cost you anything and it worked it my case. In fact I
have to do it every year due to poor quality gas.
First drain the gas tank completely along with the hose to the carborator.
Next either *temporarily* plug or otherwise stop any ability for liquid
to come out of the hose. Vice grips on the end works fine if placed right.
Leave the hose attached to the tank however and remove the tank from the
mower. Put about 1 cup of Varsol into the gas tank. Screw on the lid for
the gas tank so it won't leak. Shake the tank vigoursly for about a minute
or so. Drain the fluid from both ends - the tank and the hose.
After a years mowing the filter at the bottom of my gas tank gets so
clogged with gunk that it changes colour from silver to black. You can
check by draining the tank and looking at it carefully if it's visible.
I went for two years having to start it with ether the first time every
year. Even took it in for service with no improvement before I figured
this out. Now it will start on choke first pull when it's 45 degrees F.
If its a 70s mower with a 10-year-newer B&S engine, that would mean its
an 80s-vintage B&S. That would be about the lowest point in the armpit
of quality of B&S carburetors, and it agrees with your symptoms. The
"pulsa-jet" carbs of that era used the vacuum pulses of the intake
runner to operate a diaphragm that pumped fuel up from the tank to the
carb. They also had a vacuum-operated choke that had a tendency to not
choke enough when cold and choke too much when hot. They tended to work
fine once you got them running, but they were HARD to get going the
first time because there just isn't enough vacuum pulse to pump the fuel
while you're yanking the rope. Especially when they aged a little and
the pump diaphragm got a little stiff You could try a carb rebuild kit,
but frankly the only way I ever made an 80s Briggs run truly great was
to scavenge the carb (and fuel tank) off an older (70s or even late 60s)
I got a new diaphragm, but looking at the old diaphragm, it looks to
be intact and in good shape. The material still seems pliable, I held
it up to a light and can't find any breaks in it, including where the
choke plate rod is attached.
The longer of the two pickup tubes had a fair amount of crud on the
screen, which I've cleaned off. Gonna put it back together with the
old diaphragm and see if it starts any easier with that pickup cleaned
off. If it does, I'll store the new diaphragm in the refrigerator for
And why are there two pickup tubes and why are they different lengths?
##### Look... When this sort of thing happens, most of us want to fix it,
not to analyze it. I have had it happen lots of times over the years, and
is usually because of crud buildup in the fuel and/or the diaphragm. I have
found that you save time by cleaning out the tank, cleaning the carb, and
replacing the diaphragm. You can do this in a half hour in most cases.
The diaphragm, IIRC, is not a ballbuster in price.
##### And this is also not unusual, especially when one has starting
#### You must like to work on these engines.
I normally keep one or two of the diaphragms around. But I wouldnt put an
one back in for anything. It is a waste of time to fiddlefart with this
you have a lot more expensive diaphragm that I am accustomed to buying.
Or have a lot of time on your hands
I wouldn't think the two would be mutually exclusive.
To me there's a recreational aspect to it, absolutely.
I don't like tossing out perfectly good parts and if I can get more
lifespan out of a part I'm all for it. Learning something and
troubleshooting are also part of the goal. If I just slap a bunch of
pieces on, even if it works I don't really learn what was causing the
There ARE no "perfectly good parts" on an 80s vintage Pulsa-Jet
The old Vacu-Jet worked a lot better, but didn't have the "automatic"
(automatically applies exactly the wrong amount of choke every time)
choke feature I guess.
A diaphragm that has been in service for some considerable time, then
is taken out and allowed to dry, might work a while longer, but....
if you want to mow the yard or till the garden, it is foolish to go in and
clean the carburetor and not install new elastomer parts, IMHO>
I don't know what the part cost, but it should not have been more than a few
dollars. Chances are if the new part was put in it would be good for life.
If I had gone that far I would not worry about an inexpensive part. Even if
it had been an expensive part I would use the new one and maybe save the old
Reminds me of what hapened at work. We had a large varitable speed moror
drive to go out. Called in a factory man to work on it. He found two bad
diodes. There was a third diode (three phase circuit) and I asked him to
replace it also. He said it was $ 200. I told him to go ahead. If it went
out that $ 200 was nothing to what it would cost to get him back in and the
ammount of downtime on the equipment.
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