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

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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).
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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.
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David Martel wrote:

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

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.

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Sorry. Remove the air filter and give a big squirt straight down the carb throat.
Have played with the needle

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.
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No, this B&S, has the choke-o-matic carb where the choke is naturally shut, but opens via vacuum acting on a diaphragm between the carb base and fuel tank under it.
It will have a main fuel mixture screw and idle speed screw. As you say base setting is 1 1/2 turns out with a 2/3 ful fuel tank. This is important. Mixture strength varies with fuel level (yes, crap B&S design!)
Usually have to set them slightly on the rich side so they'll accelorate cleanly from idle (which should be a fastish 1750rpm) without dying, yet run at full speed without being too rich.
Tim..
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snipped-for-privacy@hotmail.com Wrote:

The problem you have is the diaphragm has gotten hard from sitting to long. The carb. thats on that engine is called a Pulsa-jet one of Brigg sorriest designs, The part number for a new diaphragm is 391681, Th spring you speak of is not supposed to be very springy. Even Me being Seasoned Master Service Technician I have troubles getting one of thes carbs. to perform properly so I know you are fighting a loosing battle My suggestion is to contact your local repair shop and ask them if the have a used Pulsa-prime carb. and tank assembly they will sell you This Pulsa-prime is a newer design and very easy to set up and repai if needed and it will indeed bolt right on your engine. Lots of Luck
-- restrorob
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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
: 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). :
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Pop wrote:

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.
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: 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
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the
removed
played
to
it's
If your carb has a little metal "box" cover on it , then you have an automatic choke. If not, it's a Choke-A-Matic.
If you are trying things out with the air cleaner removed, be sure to reinstall the stud...

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Let me clarify a little if I can. Off to one side of the carb there will be a rectangular cover that's split on the diagonal if you have an automatic choke...

to
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Rick wrote:

My hayter from that period has a choke that is closed by moving the throttle past maxiumum rabbit to choke.
When the throttle is reduced to top rabbit, the choke has a spring that aligns the plate with the airflow.
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Rick wrote:

The PDF diagram shows a diagonally split cover. I will give it another look tomorrow, maybe check within that cover for movement. Will try running with the air cleaner off temporarily - let's hope the stud (I assume we call it a 'bolt' here) keeps the petrol spray in order. Thanks all. Will keep you informed of progress - let's hope we can fix this for minimal expense. Goodnight.
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a

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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...
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Rick wrote:

I had one of those years ago that i had a problem with. As i recall, the carbs or fuel tanks mounted on them warped causing fuel feed problems. At one time, there was some sort of repair kit for this. Or, you put a new fuel tank on it. I would start with a new carb kit either way. Make sure too the keyway in the flywheel is not sheered and the flywheel to keyway position shifted.
Bob
-
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snipped-for-privacy@hotmail.com wrote:

Ive got that model, from the mid 80's tho.
I had a huge problem with mine, traced eventually to te fact that when it had been serviced and teh head overhauled, they had failed to set the thibng up so that it had any choke on 'maxiumum rabbit' whatsoever.
It may be that yours has a similar problem in reverse - the choke is permanently on. That, or a bolcjeked air filter, are all I can think of to suggest rich running - which will be lumpy, smoky and prone to stalling when hot.
Pull the air filter right off and try again, and see whether the choke is in fact working correctrly. From memory it should be spring loaded to flap inline with the airflow when not required. It may simply have gummed up.
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Hello everyone! I have a Briggs and Stratton 3.5hp engine fitted to a Hayter rotary mower from the mid 1970s. CY: I thik they used breaker points back then.
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 CY: They had some defective Champion plugs. Do you have another brand available?
and air filter foam element (old one was disintegrating, saturated new one with oil and squeezed excess out), filled the sump with fresh oil CY: Those 3.5 HP engines typically took 16 to 20 ounces of 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 CY: Those, typically the carb adjustment screw is right all the way in (gently) and then out 3/2 of a revolution.
(I have found I can start it and get it to idle very slowly with the throttle lever set to minimum). CY: Hmm. Can't remember what that means.
Do I need to play with the idle adjustment screw? CY: Sure, try it. Might also need new breaker points, or to have the points cleaned.
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? CY: I'd try to run it again for awhile, and burn the oil out of the system. Also can clean the spark plug with a squirt of ether spray to rinse off the plug.
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). CY: Done so.
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g'day james,
at this point i would suggest the carby needs a good overhaul not much in them but i would think the diaphram would not be working too well after all that time being dry.
snipped With peace and brightest of blessings,
len
-- "Be Content With What You Have And May You Find Serenity and Tranquillity In A World That You May Not Understand."
http://www.users.bigpond.com/gardenlen1
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Update: had a go with it this evening (air filter off, bolt back in). Choke plate opens, engine runs rich for 15 seconds or so, then cuts out. Petrol mist seen in carb throat. No luck from needle valve adjustments (thanks D. Martel). Governor has to move a long way before it takes up the slack in the spring I've noticed, and the idle speed screw doesn't hit the end point. Have emailed local friendly B&S dealer about carb overhaul parts pricing/availability. It's all so frustrating as it's a nice bit of kit and too good to get rid of.
Will let you know how I get on (maybe a week or so). James
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on an engine that old,id replace pointsand condenser,rebuild the carb ,check flywheel key to see if sheared and snug up all the bolts. lucas
http://www.minibite.com/america/malone.htm
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