Briggs & Stratton 3.5hp running too rich? (Cutting out)

[jamesbsound@hotmail.com]

Hello everyone! I have a Briggs and Stratton 3.5hp engine fitted to a
Hayter rotary mower from the mid 1970s. The Model number is 92982 and
the Type number is 1640-01. It's a 4 cycle, single cylinder, L-head,
air-cooled engine for information.
The problem is I have had it sitting idle for 5 years as the starter
rewind spring broke and lack of time prevented getting it sorted
sooner. Last week I bought a new spring, rope, (approved Champion/B&S)
spark plug and air filter foam element (old one was disintegrating,
saturated new one with oil and squeezed excess out), filled the sump
with fresh oil and put in half a tank of fresh 95RON unleaded.
So far, so good. But pulling the rope and some carburetor needle valve
tweeking got the engine to start eventually, burning off the oil I had
put in throught the spark plug hole. It then splutters and pops (rich
mixture burning within the exhaust?) The spark plug has looks like it's
not running lean (fuel/oil on it). It then cuts out (maximum of about
15 seconds after starting). Then you can restart straight away. Any
ideas as to the adjustments I need to do (I have found I can start it
and get it to idle very slowly with the throttle lever set to minimum).
Do I need to play with the idle adjustment screw? Is there the
possibility that the carburetor needs new parts too? I've heard B&S do
carburetor kits - how much would I be looking at (UK Pounds) and what
parts do they contain - anyone ever used one?
I know this is a long posting, but i'm not too hot on my knowledge of
getting carbs to work perfectly for a smooth idle.
Thanks in advance. (This email address is invalid because of spammers
so reply on here).

[David Martel]

James,

These things are generally in two groups: the three screw group and the
two screw group.
Let's take the two screw group first. You'll need a screw driver and a
spray can of starter fluid (ether). The two screws are a mixture screw (the
needle valve) and an idle speed adjustment. Screw the mixture screw all the
way clockwise and then back out 1 1/2 turns. Give it a shot of starter fluid
and start it. Adjust the idle speed if necessary so that it runs at idle.
Let it come up to operating temperature. Now adjust the mixture screw
counterclockwise (you enrich the mixture). It should begin running quite
well at some point, continue adjusting the screw ccw and it should begin to
run rough. Note this position. Turn the screw cw (you lean the mixture)
until the idle becomes rough. Note the position. Usually about half way
between these two positions is the proper adjustment. You may need to fine
tune slightly. Now that the mixture is set adjust the idle speed screw by
reducing the engine speed at idle until the engine almost stalls. Increase
the idle speed slightly above this and you are done.
A similar process is used in the three screw group . There is a low speed
mixture, a high speed mixture, and an idle speed screw. Screw both mixture
screws in all the way,cw, then out 1 1/2 turns, ccw. Give it a shot of
starter fluid and start it. adjust the idle speed if necessary so that it
does not stall. Let the engine warm up. Now adjust the low speed mixture
screw as described in the above paragraph. Adjust the idle speed screw as
described above also. Now set the engine to full speed and adjust the high
speed mixture screw as you adjusted the low speed screw. OK, the two mixture
screws interact slightly so you now need to repeat the process of finding
the points at which the mixture screws cause rough running and setting the
screws half way between these points.

Good luck,
Dave M.

[Pop]

It sounds to me like the carb might need a good degunking.
Probably plugged or partially plugged jet/s. Try screwing the
needle valves in (gently!) and back out a few time,s then put
back to where they were and see if it helps. If not, perhaps
something's plugged.
You did check for a waterlogged/plugged fuel filter, right?
Fuel's getting TO the carb?

HTH,

PopS


<jamesbsound@hotmail.com> wrote in message
news:1127654502.933671.127200@g44g2000cwa.googlegr oups.com...
: Hello everyone! I have a Briggs and Stratton 3.5hp engine
fitted to a
: Hayter rotary mower from the mid 1970s. The Model number is
92982 and
: the Type number is 1640-01. It's a 4 cycle, single cylinder,
L-head,
: air-cooled engine for information.
: The problem is I have had it sitting idle for 5 years as the
starter
: rewind spring broke and lack of time prevented getting it
sorted
: sooner. Last week I bought a new spring, rope, (approved
Champion/B&S)
: spark plug and air filter foam element (old one was
disintegrating,
: saturated new one with oil and squeezed excess out), filled the
sump
: with fresh oil and put in half a tank of fresh 95RON unleaded.
: So far, so good. But pulling the rope and some carburetor
needle valve
: tweeking got the engine to start eventually, burning off the
oil I had
: put in throught the spark plug hole. It then splutters and pops
(rich
: mixture burning within the exhaust?) The spark plug has looks
like it's
: not running lean (fuel/oil on it). It then cuts out (maximum of
about
: 15 seconds after starting). Then you can restart straight away.
Any
: ideas as to the adjustments I need to do (I have found I can
start it
: and get it to idle very slowly with the throttle lever set to
minimum).
: Do I need to play with the idle adjustment screw? Is there the
: possibility that the carburetor needs new parts too? I've heard
B&S do
: carburetor kits - how much would I be looking at (UK Pounds)
and what
: parts do they contain - anyone ever used one?
: I know this is a long posting, but i'm not too hot on my
knowledge of
: getting carbs to work perfectly for a smooth idle.
: Thanks in advance. (This email address is invalid because of
spammers
: so reply on here).
:

[jamesbsound@hotmail.com]

Pop wrote:
> It sounds to me like the carb might need a good degunking.
> Probably plugged or partially plugged jet/s. Try screwing the
> needle valves in (gently!) and back out a few time,s then put
> back to where they were and see if it helps. If not, perhaps
> something's plugged.
> You did check for a waterlogged/plugged fuel filter, right?
> Fuel's getting TO the carb?
>
> HTH,
>
> PopS

I'm thinking too that it's gunked somewhere. Fuel _IS_ getting to the
carb (if you pull the starter rope gently with the air filter removed
you are met by a mist of fuel around the choke valve). Haven't played
with any fuel filters. Is there supposed to be some sort of linkage to
open the choke plate? It's just that I can't see how it opens on it's
own (vacuum effect???) and that would explain richness symptoms on
the(new) spark plug and exhaust output popping.

[jamesbsound@hotmail.com]

David Martel wrote:
> James,
>
> These things are generally in two groups: the three screw group and the
> two screw group.

(I can confirm it's a two screw carb).

> Let's take the two screw group first. You'll need a screw driver and a
> spray can of starter fluid (ether). The two screws are a mixture screw (the
> needle valve) and an idle speed adjustment. Screw the mixture screw all the
> way clockwise and then back out 1 1/2 turns. Give it a shot of starter fluid
> and start it. Adjust the idle speed if necessary so that it runs at idle.
> Let it come up to operating temperature. Now adjust the mixture screw
> counterclockwise (you enrich the mixture). It should begin running quite
> well at some point, continue adjusting the screw ccw and it should begin to
> run rough. Note this position. Turn the screw cw (you lean the mixture)
> until the idle becomes rough. Note the position. Usually about half way
> between these two positions is the proper adjustment. You may need to fine
> tune slightly. Now that the mixture is set adjust the idle speed screw by
> reducing the engine speed at idle until the engine almost stalls. Increase
> the idle speed slightly above this and you are done.

Where would I give it the starter fluid? Have played with the needle
valve and got it to the point where starts but it won't ever tick over
until operating temperature is reached. Which
(clockwise/anti-clockwise) raises the idle speed? I take it that the
idle speed screw is an "end-stop" which prevents the revs from dipping
too low when the throttle is lowered to it's minimum point? An
observation is that the springs don't seem to have much "springyness"
anymore and it never reaches the point where the screw touches metal.

Thanks for the ideas. I will probably have words with the local B&S
dealer about springy springs, seals, diaphragms, etc.

>
> Good luck,
> Dave M.

[Pop]

<jamesbsound@hotmail.com> wrote in message
news:1127676808.353365.297370@g14g2000cwa.googlegr oups.com...
: Pop wrote:
: > It sounds to me like the carb might need a good degunking.
: > Probably plugged or partially plugged jet/s. Try screwing
the
: > needle valves in (gently!) and back out a few time,s then put
: > back to where they were and see if it helps. If not, perhaps
: > something's plugged.
: > You did check for a waterlogged/plugged fuel filter,
right?
: > Fuel's getting TO the carb?
: >
: > HTH,
: >
: > PopS
:
: I'm thinking too that it's gunked somewhere. Fuel _IS_ getting
to the
: carb (if you pull the starter rope gently with the air filter
removed
: you are met by a mist of fuel around the choke valve). Haven't
played
: with any fuel filters. Is there supposed to be some sort of
linkage to
: open the choke plate? It's just that I can't see how it opens
on it's
: own (vacuum effect???) and that would explain richness symptoms
on
: the(new) spark plug and exhaust output popping.
:

Well, -something- should open the choke plate, yeah. Is it
staying closed or partly closed? If so, that's your problem, or
at least one of them. Sometimes it's not obvious what keeps them
open so look closely. There could be a spring disconnected that
holds it in the open position or something real simple like that.

D Matel gave you a great rundown on how to set the idle/hi speed
mixtures, BTW, so I'd keep that handy. It's "standard" stuff but
not always easy to remember and completely foreign to a lot of
people. His method will work 100% if all is right with the carb
and engine.

A closed or partially closed choke though will certainly make an
engine run rough or not at all by starving it for air. I suspect
you've come upon the problem if you're relating it correctly.
Your original post has been snipped out so I don't recall the
original details, but it's fairly UNcommon in my experience for a
small engine, esp a B&S, to operate on vacuum. At least I've
never seen one; if I'm wrong, someone will be along quickly to
correct me, I'm sure <g>.
If there is no seperate cable to close the choke, which there
probably isn't on that small an engine, it may be controlled by a
centrifugal force wire when the engine is running and the
positon of the throttle. I never thought much about it because
it's always seemed "obvious" to me when I looked at them, but
darned if I can explain it very well right now.

Maybe Mr. Martel will come back and explain; something tells
me he knows what he's talking about. Or he had a manual handy
<g>.
If you don't get anywhere and no one offers furhter
assistance, come on back after you study the choke/throttle
linkages a bit and I'll go see exactly what my B&S engines do;
have three of them.
I will say this: When you're assessing the choke plate
position, do so while the engine is running (or trying to). I do
recall that the choke plate on my push mower is mostly closed
when it's at rest, which is fine with me: Keeps the spiders out
over the winter!

HTH a little at least

PopS

[David Martel]

> Where would I give it the starter fluid?

Sorry. Remove the air filter and give a big squirt straight down the
carb throat.

Have played with the needle
> valve and got it to the point where starts but it won't ever tick over
> until operating temperature is reached.

Yes, it is now misadjusted. Screw it completely in and then out 1 1/2
turns.

Clockwise will increase idle speed. You are correct it is an end-stop.
If the screw does not touch metal. then investigate the throttle cable and
the linkages. It would be very unusual for the linkage springs to lose
"springyness".

I don't understand your question about the choke. The choke should be
controlled manually, usually by a lever. When starting the engine with ether
to adjust the screws the choke should be completely open. If your choke is
fully closed then you have discovered your problem. Find the choke control
and open the choke. The choke control may be on the mower handles or on the
engine.
Since you've fooled with the mixture screw you'll need to do the "two
screw" adjustment.
Won't hazard a guess with customs and VAT but a carb rebuild kit is
$15USD.

Dave M.

[Rick]

<jamesbsound@hotmail.com> wrote in message
news:1127654502.933671.127200@g44g2000cwa.googlegr oups.com...
> Hello everyone! I have a Briggs and Stratton 3.5hp engine fitted to
a
> Hayter rotary mower from the mid 1970s. The Model number is 92982
and
> the Type number is 1640-01. It's a 4 cycle, single cylinder, L-head,
> air-cooled engine for information.
> The problem is I have had it sitting idle for 5 years as the starter
> rewind spring broke and lack of time prevented getting it sorted
> sooner. Last week I bought a new spring, rope, (approved
Champion/B&S)
> spark plug and air filter foam element (old one was disintegrating,
> saturated new one with oil and squeezed excess out), filled the sump
> with fresh oil and put in half a tank of fresh 95RON unleaded.
> So far, so good. But pulling the rope and some carburetor needle
valve
> tweeking got the engine to start eventually, burning off the oil I
had
> put in throught the spark plug hole. It then splutters and pops
(rich
> mixture burning within the exhaust?) The spark plug has looks like
it's
> not running lean (fuel/oil on it). It then cuts out (maximum of
about
> 15 seconds after starting). Then you can restart straight away. Any
> ideas as to the adjustments I need to do (I have found I can start
it
> and get it to idle very slowly with the throttle lever set to
minimum).
> Do I need to play with the idle adjustment screw? Is there the
> possibility that the carburetor needs new parts too? I've heard B&S
do
> carburetor kits - how much would I be looking at (UK Pounds) and
what
> parts do they contain - anyone ever used one?
> I know this is a long posting, but i'm not too hot on my knowledge
of
> getting carbs to work perfectly for a smooth idle.
> Thanks in advance. (This email address is invalid because of
spammers
> so reply on here).
>

From the model number, that's a vertical shaft model with a Pulsa-Jet
carb. The diaphragm kit usually sells for a couple dollars US.

The Briggs and Stratton web site should have the owners manual for
that model...