Lawn Mower Carburetor

Yes:

1) The equipment manufacturer can. It will be in the User Manual that came with the equipment.

2) Many lawn mowers are fitted with a isolating valve at the base of the fuel tank. Once the valve is turned off the petrol remaining in the carburettor can evaporate, leaving the bowl empty. On opening the valve, the prime button can be used to refill the bowl quickly.

The hose is either a connection from the fuel tank to the carburettor or a waste hose; in the event of the latter it can direct the wasted fuel away, ideally anywhere other than a surface that is likely to be hot.

PW, pretty much answer your question.

But here's an interesting thing I recently found out. I purchased a Ryobi S430 4 cycle weedeater about (2) weeks ago.

Ran only ok the first time, but then ran like crap. It's my fault, I didn't do a more in depth research on it.... I was leaning towards the Stihl actually.

After I googled, I found out that that the carburetor is factory set to pass the emissions, and not really set to run decent. And the special tools (Pacman) to adjust the carburetor is difficult to buy. Ebay has them.

After I bought it and adjusted it, I'm very satisfied.

You can do it with out the tools, but it could void the warranty.

Its another example of the government is here to help you.

Yes, my weedwhacker would actually idle once I properly adjusted mine. Before that, the engine would die anytime I released the throttle. Opening up the throttle stop just made the engine run too fast. Same thing with my chain saws.

Until recently, I'm not really used or aware of having to adjust a new small gas engine right out of the box.

I like this weed wacker, I just got an pole attachment for pruning trees. The next on my list is a hedgetrimmer attachment.

My girl friend always had a battery operated, or a 120V cord operated because she doesn't have the know how to make these adjustments. But the Black and Decker weed wacker she bought (2) years ago, last year the battery wasn't holding a charge, and this year, it won't take a charge.

So, there are a number of other attachments for this, that if needed, I'll just pick it up.

Chainsaws, on the other hand take quite a bit of abuse in the woods.

This was the spline type of tool I purchased from a well-known on-line retailer. My Poulan chainsaws and the weedwhacker had these splined adjustment screws that were shrouded (thanks to the dastards at the EPA ) so you can't adjust them with needle-nose pliers.

Once I acquired this tool, my life went from one of ICE frustration and anger to one of productive bliss.

I noticed that this same well-known on-line retailer now sells tool kits with all the tools to adjust EPA-approved improvement-resistant mixture screws.

I've got a 10 year old Poulan and a two year old Echo.

I always drain the tank and run then till they die when I put them away.

Never had to make any adjustments to either.

if you don't use them for a while, drain may help. I understand is to fill them up to the top to eliminate the air that breaks it down into tarnish. I don't think are chainsaws (our as in on the farm use), doesn't sit idle for more than maybe a few weeks. For me. I just need it for spring trimming on the fruit trees. And since I got the Ryobi, the only quite time will be maybe 2-3 months in the winter.

I don't know what they have Stabil additives.

Mine sit much more than run. And in the desert they get really hot sitting on the self,

The only thing I don't drain is the weed eater. It gets used often enough.

you live in a higher altitude too. unless you go to MN more.

I don't do yard work in MN.

We have a "lawnboy".

funny

I was under the understanding , it was illegal? for distributors to sell these tools to work on the carbs... (because of the emissions tests). That's why they had the screws inlayed and unreachable with standard screwdrivers.

I bought mine (actually a set) off of ebay.

This anti-tampering mixture screws have been brought to you by the same people that brought you the low water use toilet.

Does a supply of John Wayne toilet paper come with that low water toilet?

No, but Look what happened to him

Technically, the legal rationale for selling the tool is to "service" the carburetor. The service technician is supposed to use the tool to close the needle valve adjustment while measuring the rotation of the stem. Then the needle can be removed, orifices cleaned and reassembled with the tool used to reopen the needle valve the same rotation as the original setting.

To do otherwise might be considered unethical in some circles.

To do otherwise might be considered unethical?

If you mean to have the engine be actually function to do what it's suppose to do unethical. Nothing unethical about that, I'm fine with that.

"In some circles"

Chainsaws can also dish out quite a bit of abuse in the woods! Do keep safety first.

My big issue with two stroke engines was when gasohol took over, and the carburetor diaphragms went bad after about a year of that. Now, my Stihl weed whacker runs and idles well. The Poulan with multiple attachments is not as old, and is sometimes still hard to start, even after a new carb install.

I have a 45 year old Craftsman Edger with a 4 stroke Tecumseh engine, but have not been able to get the old needle valve out, which needs replacement, along with the rest of the kit. Anyone have access to the instructions on these old engines, I could not find. I think I need a good six point socket about 3/8" (will have to mic it), then grind down the face of the socket so it is completely flat, and gains purchase on the brass nut that stands up about 3/64" from flush.

Then I turned around and broke the throttle lever on the wife's garden Mantis. I tried to fab one out of aluminum two pieces epoxied together, but I did not clean the parts well before gluing, and it broke the first time pressed down. Will start with a bigger part that is all one piece next time, and work it down to a clean fit.

BTW - to the OP: that little black hose is the excess return to the gas tank. Everything else you have been told already, is right, and does apply. Depress about 6-20 times and crank her up. You need to also start using some Stabilizer oil treatment to shoot into the carb when you put her away each season, so gums will not ruin the carb. Other thing to do is empty the carb (run the machine out of gas), then shoot the stabilizer in the tank and in the carb to prevent rusting, corrosion, gums.

Nothing worse than going in the woods without doing a pre check and shake down of your chain saws.

We always had three in the woods, mostly stihl. We had a hasavarna and a Sachs Delmar. And a Poulan and homesite mix in. Most of our chainsaws we bought slightly used. Usually from people that was going to save a lot of money by cutting their own fire wood. We bought 4 saws from people doing this, 1/3 price of new. 2 with only one fill of gas. The first two, the guy thought he was screwing us over. The first one, dad showed him what was wrong, and even adjusted it for him and sharpen the blade. Ran great. But he was so disgusted with it, he won't have anything to do with sawing his own. We sold firewood to him for 7 years, till he moved.

Really!!!!

Don't you know how to use a search engine?

How To Use Google To Search

Fuel Systems: Primer Bulbs

The primer bulb on a lawnmower has a simple goal, it squirts gasoline directly into the intake manifold to provide a rich mixture which makes it easier for the engine to start. If that extra squirt of gasoline wasn't provided, you would have to pull the starter cord many times to get enough gasoline to be drawn through the carb for an explosive mixture, especially important for a cold engine.

Well, sort of:

"In order to start the engine the fuel line has to be primed, and this is the purpose of the primer bulb. If its fuel line is not primed even an engine that is in perfect tune will will require a great deal of cranking to start."

From previously mentioned website.

For my old lawnmower, that was exactly the case. The primer bulb was an enrichening device. There was no 'choke' on that carb. On my weedwacker, the bulb was there to pump fuel from the tank to the carburetor so you could start it. Those carbs don't have float bowls so you need to prime the carb with fuel to get it to start. My weedwhacker carb has a choke plate to enrichen the mixture for starting.

Most 2-stroke engines rely upon induced vacuum in the carburetor throat to spray gas into the air stream. That really only happens when the engine is rotating at some speed greater than zero. One has to pull the cord, or depress the starter button, etc.

It's useless. I've given up trying to explain.

More into the weeds...on a gravity fed carb such as the kind found on most mowers, the bowl will hold the fuel at a certain level until drawn by the passage of high-speed air through the carb's throat. Pumping the primer bulb will draw fuel into the carb throat without the engine running. Pulling the starter cord will generally not draw enough air/fuel mix at slow speed...so a little help in getting some fuel up is needed.

This allows a more efficient way of wetting the air filter on a horizontal shaft engine, or just flooding the engine entirely.

Very little difference between a primer button on your lawnmower, and depressing the accelerator pedal 3 times before cranking the engine on a carbureted car. (That was usually a requirement to start a car before the days of fuel injectors.)

In a carburetor, there is a fuel jet in the throat where air velocity is at maximum. The primer bulb will squirt a shot of gasoline from the fuel tank into the jet in the throat, where the gasoline is mixed with air when you crank the engine (electric or by starter rope). This will allow the cylinder to have a fuel/air mixture. On the compression stroke, the power from that first ignited stroke will cause a powerful draft of air into the carburetor, and draw fuel into the bowl/jet, to start the continuous cycle. Hence....your engine runs.

Good comparison

Maybe, but it is completely incorrect.

Depressing the throttle was to set/engage the choke butterfly in the closed position.

Depressing the throttle three times would have simple introduced raw, liquid gasoline into the intake manifold where it would have accumulated on the bottom of the runners and not provided any useful combustion.

The accelerator pump that squirts raw fuel into the air stream of a running engine was used to keep the car from stumbling when more power was required rapidly. It is not used to "prime" the engine. Doing so was simply a complete waste of gas.

I'm not even going to begin to debate the function of the primer bulb.

No, I am correct. You are dead wrong, and your answer doesn't even make sense!!

First, you say this:

"Depressing the throttle was to set/engage the choke butterfly in the closed position."

Then, you say this:

"Depressing the throttle three times would have simple introduced raw, liquid gasoline into the intake manifold where it would have accumulated on the bottom of the runners and not provided any useful combustion."

So, according to you, WHICH IS IT?? Close the choke, or give a shot of gasoline??

How about engaging brain before finger tips on the keyboard, next time??!!

My 1983 Dodge Charger had the 2 barrel Holley carb, with feedback. It had an electric choke. Pumping the accelerator HAD NOTHING TO DO WITH THE CHOKE! The engine would not start without at least 2 pumps on the accelerator. I kept the car for 15 years from when I bought it new, so I know what I am talking about. You don't!

When the accelerator was pumped, there was a diaphragm that pumped, sending gasoline (from a small sealed bowl) through a small needle jet that would give a small shot of fuel in the carb throat, and was used to PRIME the engine with fuel for starting. The gasoline never made it the "runners" as you called them! This was BEFORE the key was turned on and the electric fuel pump delivered gasoline to the carb. So, useless gasoline to the intake manifold? Really?? How many times did YOU turn your ignition key on and just crank your engine without ever starting it? Bunches, I suspect.

And yes, this same action (fast use of accelerator) was used to advance a shot of fuel into the carb for sudden accelerations, also.

You are a very self-appointed expert who has no idea what you are talking about!!

AND YES, PLEASE SPARE US ALL FROM YOUR "DEBATE" ABOUT THE PRIMER BULB. IGNORANCE IS NOT PRETTY!

You mean like this?:

"What It Does

• A primer will pump a small amount of gas into the carburetor. Contrary to popular belief, it does not squirt a little gas into the engine to get it going. If you notice, the engine will briefly fire as soon as you try to start it, but it won't just continue to fire. This is because there is no gas in the carburetor. So, when the engine sparks and ignites the gas inside the cylinder, it can't continue to run on its own. A primer sends gas into the carburetor so it can create a fuel and air mixture that is ready to go right into the cylinder and keep the engine running." -- http://www.ehow.com/how-does_5006420_how-small-engine-primer-works.html
• All I know is when a small engine is bone dry on fuel, and the magneto is rusty, and the spark plug is fouled, and the air filter is plugged, and the on/off switch is malfunctioning - it can be a long or short afternoon, depending on how I approach the situation, and what I do first. Sometimes beer is the answer.
  

A good cooler, filled with ice and beer, is one of the necessary tools for starting yard work! So, you are obviously a well equipped do-it-yourselfer!

I have a gas edger (the type with the rotating steel blade) that gave me fits. Turned out, the diaphragm in the carb had pin holes in it. Always acted like it wanted to run, but NOTHING would keep it running. No matter what else one tried to do with it.

I was downing my second brewski when I got the call back from the parts store that the diaphragm was obsolete, no replacement part available.......

Yes, small engine carbs and vehicle carbs have differences. One big one is an electric fuel pump on a vehicle......

I have a carb kit at my shed for a Tecumseh engine on a very old Craftsman edger. I have yet to be able to remove the valve seat for the needle valve during the carb rebuild. I think it is tool-time, or to be more precise, toool-making time.

James, I give you 3 thumbs up for being an outstanding mind reader!

Yes, mine is a Tecemseh 2 cycle edger. 1.5 hp. Didn't get it at Sears, though. Got it at the now also obsolete Hechinger's home improvement store in Virginia, back in 1991.

I am told that Walbro has a diaphragm for it......true? Or, perhaps replace with a Walbro carb?

That part is above my pay grade. Mine is 4-cycle, though. The hex nut for the valve seat only rises above flush in the chamber about 1 mm, and a regular socket will slip off it every time. Pretty sure since it is old and American that it is not metric, and that I can't find this same carb. You and I may be forced to spring for a "look-alike" carb if we can find 'em and make our own adapter plates for them. That could be fun, since I have no mill, but a buddy does, a good one.

I will try grinding down the correct size 6-point socket so it's flat at the opening, and try one last time, then it may get wild with the propane torch heating to "open-up" stuck threads? If I don't put my eye out, and it works I will let everyone know, since I tend to crow at the least provocation. I was able to get the carb kit, a couple years ago, but I do not remember now where that was on the internet. There are plenty of small engine places on the web.

If you local a local lawnmower shop (we have Paul's Parts here in Lubbock), they should be able to assist, with advice, if not with the parts.

James, I recently had to replace the needle in a carburettor (Walbro) on a Stihl brushcutter. The needle had jammed with ethanol fuel over a period of storage and the top tit had broken off with nothing to grasp - even with fine longnose pliers.

I procured a replacement carb kit which happened to have the needle and spring and all replacement parts for the grand sum of $NZ4.50 ($US2.60)from here. All the parts fitted perfectly and it is back running.

http://www.banggood.com/Carb-Repair-Rebuild-Kit-for-Walbro-K20-WAT-K20-WAT-p-1009709.html

I noticed that there are some Tecumseh and other brand complete carburettors available and you may also find some replacement parts you may need.

http://www.banggood.com/Alloy-Carburettor-Carburetor-For-Tecumseh-640350-640303-640271-LEV-p-939998.html

This is not intended as a recommendation, just for useful information.

I did email that to my cell phone for later perusal, although the carb shown is not the one for my old engine, at least I think it is not. It has a really shallow metal diaphragm protector at the bottom, no tubes protruding, and no priming bulb (just gotta love it).

I am about ready to make some hydrogen, oxygen, and see if its enough to run this thing without blowing up my generator for the gases. If it turns out to be HHO style "over unity, I can run an alternator and back feed the power to the electrolysis and keep it all running as a "do nothing" machine. If under unity, everything comes to a halt at some point, if far enough over unity then maybe I can charge a battery off to the side?

Right now, just a bit more than skeptical.

On many modern vehicles, flooring the accelerator 3 times with key on will reset the oil change timer......

It does that on my old Chevy pickup.

The purpose of the primer system is to remove air from the system to allow the fuel to feed the carb by siphoning. One of the hoses returns to the fuel tank and the other feeds the primer bulb.

You are only half right.

I just rebuilt my weedeater carb and my tiller carb this past weekend. New fuel lines and primer bulbs also.

The primer bulb does 2 things:

It primes, or fills the fuel lines, yes. (This is where your knowledge stops.)

It primes and fills the carb also. The fuel is not fed from the fuel tank by siphoning action. (Many small engines have the fuel tank below the carb.) After priming, the fuel is fed by a spring-loaded diaphragm PUMP inside the carb. Vacuum from the piston stroke causes the diaphragm to move, pumping the fuel from the tank to the carb, so the engine can run in nearly any position of the carb relative to the fuel tank.

ANOTHER self-appointed expert who hasn't done his homework.......

I refuse to do homework when I am at home working on home work projects.

If it hits and runs, I am happy, if not, then I get blisters from pulling the damn dern gol-darned cord. I can usually figure it out, unless I have to break out the DVM and start checking switch, mag, etc. for continuity. Did I fail to mention my dog likes to chew the wires?

Does your dog only chew on the wires of working.....or non-working...small engines?

If it works, an easy cure for the dog chewing the wires is to pull on the starter rope....

And don't get me started about "testing" my old halon fire extinguisher......(when I pulled the spark plug, left the plug wire ungrounded and dangling.....and gasoline pouring out of the carb from a bad needle valve......AND PULLED ON THE STARTER ROPE.....)

Yea.....one of my more productive days of my youth.......

Yikes! How long did that take to heal?

All weekend for my pride......and not a beer in the house, at the time.

Nothing was in my way when I made a mad dash to the kitchen for the halon bottle. So, didn't burn through any wires or plastic or paint.

Guess I should have sued the mower manufacturer for not stating in the owners manual, and not having a sticker, that said, "When needle valve sticks open gasoline will fill up cylinder. Remove spark plug to empty cylinder of fuel. DO NOT PULL STARTER ROPE WHILE GASOLINE IS POURING FROM CYLINDER! A (GREATLY) ACCELERATED REMOVAL OF GASOLINE WILL RESULT! (and elevated temperatures....)"

You are free to believe your own version of reality no matter how wrong you are.

And this, obviously, you learned by much experience.....

But hey, whatever floats your boat....

The correct answer is "It depends on the carburetor." I designed this stuff for 10 years.

Small two stroke carburetors come in two flavors. One has a float bowl, the other doesn't.

The ones I am most familiar with do not have the float bowl. The carburetor has a throttle needle valve and an idle needle valve. The draw gas from a small chamber on one side of the carburetor. That chamber often is closed off on one side with a spring loaded diaphragm that operates a stop valve and is fed from a second chamber that also is closed off on one side with a second diaphragm. This second chamber is a fuel pump that uses vacuum from the intake manifold to oscillate the diaphragm and pump fuel on the other side of the diaphragm.

In carburetors of this type, the primer bulb pulls fuel from the fuel tank, through the fuel line and through the pump chamber. from there it goes to the primer bulb and then back to the fuel tank. The carburetor counts on manifold vacuum and pressure to cycle the pump diaphragm and move fuel to the second chamber and into the airstream through the needle valve. There are also two or three ball check valves or flapper valves that keep the fuel moving forward.

Most float bowl carburetors don't have primer bulbs, but those that do usually inject fuel into the carburetor venturi or into the intake manifold.