I am fixing a Toro Super Recycler (20043) for a friend. It's has a 6hp
Briggs engine. It has no throttle (auto throttle?). I have replaced
the plug, fuel line, and air filter. I also rebuilt the carb including
new gaskets. I cannot get the mower to start. If I add a few drops of
gas into the cylinder then it starts right up and runs like a champ. I
can even shut the mower down and it will start right up again. But if
you let it sit for a day, it will not start again.
Its a primer system but its an odd setup as the primer bulb is on the
The throttle / governor seems odd to me also. A spring pulls in one
direction holding the throttle open while a air vane on the engine
pulls the throttle closed. So while running the throttle is in
equilibrium between the two. The odd thing about the setup is that
when you are starting the engine, the throttle is wide open.
Thanks in advance.
The governor is typical for many small engines that run at one speed.
It sounds like this engine is not getting the extra fuel it needs to
start. Check if there is a choke that is not working. If there is no
choke then the primer is the only means of adding the extra fuel, be
sure the primer is delivering fuel. A small crack in the primer bulb
can really limit the fuel delivered.
The bulb is fairly new. It does have a small hole in the center
though. (It's supposed to be there.) When you push the primer bulb,
air is pushed though some channels in the back of the air filter
between the air filter and a gasket. The gasket is new. I think the
air then blows into a small hole slightly pressurizing the fuel and
pushing vapor out of an even smaller hole into the intake. (or maybe
using the venturi effect)
That makes sense though that something is not quite working in that
area. I know the holes in the carb are clean, but I think I could
clean up the primer system a little better.
Quick question: Do I need to oil that gasket? it seems like it would
make it more air tight and increase the amount of air getting to the
I will post tonight on what I find out.
Thanks for the help.
As others have already said, that air pressure should be causing some
fuel to squirt into the carb's intake passage.
I haven't personally encountered a primer bulb with a hole in it, but
probably it's covered by your thumb when pushing it and is there to let
things equalize when you're not.
My best guess is that maybe there's a tiny valve ball or sumpin' like
that in the carb which might be stuck closed, or maybe even fell out
unoticed when you rebuilt the carb.
Might be you're going to have to open up that carb up again and compare
things with an accurate exploded view of all its parts to figger out why
the primer isn't having its expected orgasm when you push on its bulb. <G>
What is the engine model & type number? Date code would help also because
some engines were slightly different over the years.
One of the easiest checks is to remove the air filter cover and filter,
prime the carb and see if there is any fuel in the carb throat. If there is
fuel, then you have a problem with either a gasket leak or compression
and/or valve problem. One way to check that is to do the same as before but
start the engine. As the engine is running, slide a finger over the carb a
small bit at time so that you are creating a choke effect. If the engine
starts to stall, then you can rule out a fuel problem or gasket leak. If the
opposite is true, then look at those. This is also a trick used for other
types of engines too.
One thing that most people miss when servicing small 4 cycle engines are
the valves. The exhaust one being a culprit alot of times because of the
heat that passes by the valve face and either burning it or causing carbon
build-up. I'm not saying that is your engine problem but keep it mind if
everything else checks out ok. Many times Techs will change both valves plus
the headgasket when an engine hasn't been serviced for quite a while. One
bad habit that many people have is leaving an engine in a damp place with
one valve open. The valve stem may corrode enough to stick it open a little
and cause backfire as I've seen that many times.
Not that it makes a whole lot of difference, but I'm a Tech and if you need
any other info, I'll try to reply if possible.
I have that with one of my lawn mowers. I use starter fluid in an
aerosol can. That might be more convenient for you. No need to take
off the air clearer, if you do that.
It's good for a couple hours of not running after I've run it. Not
sure how much longer before it won't start again.
That's standard. AFAIK they all have a choke that closes when the
throtlle is in the start position, but you don't have a throttle. I
have two lawn mowers that also don't have one. I don't like it.
Maybe that means you and I don't have chokes????
When the grass isn't heavy, I want to slow the engine so it doesn't
make so much noise, and these mowers don't provide for it.
The noise drives me crazy. It's a push mower. Why do people put up
One of them has a place where I could probably mount a throttle --
should I? -- but the other has no place at all.
Remove NOPSAM to email me. Please let
me know if you have posted also.
Cleaned the primer system tonight. Everything went back together very
I removed the air filter and tried to see if fuel would appear if I
primed the carb. I didn't see any fuel at all. Later, after I pulled
on the start cord there was gas in there, but it just sat on the bottom
of the carb.
Couldn't get it started so I used some started fluid to get the engine
going. I could definately see the fuel comming out of the jet at that
point. I also did the test of starting to cover the intake and the
engine would almost stall and even made a quick puff of dark smoke.
Once its going it runs forever.
Here is a web page of some pictures of the intake, mower, governer, and
model numbers. Maybe it will help.
Thanks for all the help. I do think its not getting enough fuel though
priming. As to the next step I am unsure.
I should mention that the advice I'm giving you is from my experience
servicing small engines of kinds. However, it is really hard at times to
explain all aspects of repairing if I don't have the engine in front of me
to examine. I can give just general idea of what may be wrong and how to
repair it, but that's about all.
It sounds like you may have a plugged passage or leak in the primer circuit.
You didn't say how you cleaned the carb and related parts so I'm guessing at
what is happening, which I absolutely hate doing. Anyway, it's most likely
there is a leak because of the way this circuit works. It's the rapid push
of air through the carb that forces fuel into the carb throat (venturi). You
will have to take off the air filter base plate and look for anything that
maybe causing a leak between the plate and carb. If ok, follow the circuit
from the primer bulb through to the venturi. The more a person understands
in how it works the easier it is to diagnose the problem. I've found that
most of the time, engine problems are caused by something quite simple but
frequently hard to spot.
If everything looks ok, then you will have to take out the primer bulb and
see if there is anything plugging the passage behind it. The primer bulbs
themselves can be a problem because the rubber they are made of does not
like unleaded gasoline. They have a tendency to turn into mush after a while
or get rips in them. The ring that holds the bulb in can be a pain in the
butt taking out so try not to damage if possible. If you have any doubts of
how good the bulb is, just replace it because they are not very expensive.
Try these ideas and post your results.
I will try to explain the priming system up to the point where I am not
sure what it does anymore. The bulb is located on the side of the air
filter mounting plate. When you push it the air moves down a cone and
then runs though a small channel around the top of the carb inlet. The
channel is half made by a groove in the air filter, and it is enclosed
by the gasket that fits between the air filter mount and the carb.
Then the air comes out a small hole, and goes into a small hole with
about a 1mm diameter in the side wall of the carb intake mount. Here
is where I get lost. It's hard to follow the internal channels of the
carb. There are 2 holes pointing back at the air filter that I think
have something to do with it. One is large at about 3mm diameter and
the other is very small, closer to .001 of an inch.
When I cleaned the carb I disassembled every thing I could and actually
washed it in a water/soap bath. I used an old toothbrush to clean all
the crevices. I also used a small wire and ran it though all the
passages I could find. I didn't really see any crud come out. I would
also note the the carb, before I cleaned it looked fairly clean. I
then rebuilt the carb using new o-rings and gaskets. Everything was
clean and dry when i put it back together. One thing I didn't remove
was the half circle plug on the underside of the carb. I didn't know
its purpose and didn't want to mess it up.
As for the intake, its all plastic. I removed the bulb and thoroughly
cleaned the channel.
The bulb itself appears to be blowing the appropriate amount of air. I
think that I can also feel air come out of the 2 small holes I earlier
described. It's like it just not picking up any gas.
I think if I understood the theory on how the primer was suposed to
work, then that would help. Like, when priming, what hole should the
gas come out of? Are there any ball valves that could be missing?
Serendipitously, on another newsgroup I haunt (rec.crafts.metalworking)
the same question came up and I'll paste the poster's explanation of how
the primer bulb system works here:
The float controls the level of gas in the float bowl, most carbs have a
small air inlet to keep it from air locking. On the primer bulb models,
this air inlet is hooked to the primer bulb. When you squeeze the bulb
the air pressure forces the gas down in the float bowl, and up into the
main needle, dumps raw gas into the carb throat. As soon as you remove
the pressure, the float needle opens a bit to replace the gas that was
pushed out. Radically simple.
Now, that makes elegant sense to me on a carburetor with a float bowl,
and that hole you mentioned in the center of the bulb may well provide
the bowl vent.
So, take off from that point and see if you can figure out why the
primer isn't doing it's thing. If it's supposed to work on the principle
described above, then I'd have to assume that there's a leak from the
carb bowl to atmosphere preventing pressure from building up and pushing
gas out the main needle valve. Try
But some carbs which mount right onto the fuel tank also use primer
bulbs, and those must work on some other system. Maybe there's just a
couple of little ball check valves which facilitate the pumping action.
I had a mower that would start and then quit after 5 minutes. Wait
10 minutes and it would start fine.
The problem was the gas cap. It had a washer and rubber gasket in it
and a tiny hole in the washer. The gasket was deteriorated and
stopping air from entering the gas tank. We just loosened the cap and
There is a possibility you have a vacuum in your gas tank. Once
running, the vibration cures the problem.
Its fixed! Here is what I found. When I described the primer system I
talked about a channel running around the intake, and puffing air into
a small hole. Well I was watching the primer last night and put a
little water around the orfices to see where air was blowing. It was
actually leaking from that channel, and never making it to the carb.
Its a plastic air filter mount and didn't make a tight fit. I took
some gasket maker and used it to attach the gasket to the channel and
used some to build up some volume so that the intake would fit snuggly
against the air filter mount. After letting it cure over night, I
pushed the primer bulb and gas spilled out! It came from the main jet.
It runs like a champ now! Thanks for all your help.
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