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B&S Push Mower Carb Issue

02/10/2015 9:14 PM

Hello! It has been a while since my last post on Cr4! My push mower has a 450 Briggs & Stratton engine. The problem I am noticing is that the carb does not aspirate fuel from the tank. As I had a set of replacement parts, I disassembled it, sprayed the carb thorougly with 3M carb cleaner and placed a new diaphragm / gasket and priming bulb. Once reassembled I noticed the priming bulb still did not work. I checked that the bulb sits correctly and that the retainers of the fastening ring were in position. By placing some fuel directly into the carb, the engine runs well for some minutes until gasoline runs out. I have the feeling one or more of the little spring operated ball valves of the carb may be stuck ... but no idea which one to check. Any clues? Thank you!

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#1

Re: B&S push mower Carb issue

02/10/2015 9:29 PM

Check them all.

Have you blown all the passages out with an air gun?

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#29
In reply to #1

Re: B&S push mower Carb issue

02/12/2015 9:29 AM

Sounds like a plan, there's a finite number of ball valves, and the number should be low (carburetor's are not known for overwhelming complexity, more pedal(1) = more fuel in the mix.), so this looks like the point where 'shotgunning' the problem is a time saver.

Notes:

1) I'm using the automotive analogy here, since those are the ones with the most complex carburetors. Mowers, since they have smaller, simpler engines should have even simpler carbs.

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#2

Re: B&S push mower Carb issue

02/10/2015 9:29 PM

Before I paid someone to maintain my lawn I had a riding mower. When Florida started putting ethanol into the gas I was forced to join the Carburetor of the Month Club.

The ethanol was deteriorating the rubber inside the carb and the fuel line and subsequently clogging the smaller portals and jets inside the carb.

You might want to inspect the rubber fuel lines and gaskets to see if when swiped by a clean white cloth if they turn black. This could indicate that rubber born contamination is fouling the smaller passages of the carb.

You may also want to call your local mower and small engine repair shop with your symptoms to see if they know what the cause may be.

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#30
In reply to #2

Re: B&S push mower Carb issue

02/12/2015 9:33 AM

"When Florida started putting ethanol into the gas I was forced to join the Carburetor of the Month Club."

I avoid the whole issue with my electric power. Let's SEE them try to cram '10% ethanol' down a SOLID COPPER WIRE! MUAHAHAHAHA! (thunder crash)

Oops, let my 'German Mad Scientist' side out there. Sorry, everyone, I'm sorry, my bad, that one's on me.

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#3

Re: B&S push mower Carb issue

02/10/2015 9:58 PM

These are usually pretty easy to work on. Did you remove the fuel pickup tube and make sure it isn't stuck/clogged? Remove it, make sure you can blow through it from bottom to top. At least some of them have a check ball which prevents blowing from top to bottom. And make sure the screen is not clogged. You did empty and clean out the tank, I assume?

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#10
In reply to #3

Re: B&S push mower Carb issue

02/11/2015 11:15 AM

Right, I emptied and cleaned the tank, also the screen filters and pickup tube.....

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#14
In reply to #10

Re: B&S push mower Carb issue

02/11/2015 12:45 PM

I think that's called a new style PulsaJet carb. (Some of the older ones had an adjustable jet and/or no primer bulb. And a removable side cover.) Basically, the diaphragm and flappers pump gas up into the well in the top of the tank. There is an overflow slot in the top of the well that lets excess fuel go back into the tank, so it maintains a constant level for the jet circuit, whether the tank is full or nearly empty. From the well, the jet meters the gas up into the venturi.

You might be able to determine whether the problem is in the pump or in the metering circuit like this: assemble the carburetor to the tank without any gas in the well and install it on the engine. Pull the starter rope several times. Then carefully remove the carb from the tank and see if any gas is in the well. If so, the pump is working and your problem is probably a plugged jet/metering circuit. If not, something in the dip tube/pump is either plugged or has a leak. Make sure the vacuum passage to the back side of the diaphragm is clear and the choke flapper mechanism is working.

You can Google (of course) 'pulsajet' to see the principle of operation and a more detailed overhaul procedure. Keep at it.

I think this one is yours http://outdoorpowerinfo.com/repairs/briggs_pulsa-prime_carb.asp

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#16
In reply to #14

Re: B&S push mower Carb issue

02/11/2015 7:06 PM

right, thats my carb! Following the info on this site I will take a look at the primer valve and the check valve seat I did´nt know how to disassemble. Thank you!

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#4

Re: B&S push mower Carb issue

02/10/2015 10:39 PM
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#5
In reply to #4

Re: B&S push mower Carb issue

02/10/2015 11:14 PM

I think he's ready for part 2:

https://www.youtube.com/watch?v=CRJBuHdDHAA

Ole Scotty's accent was a bit much for 10 minutes to remove the carb.

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#24
In reply to #5

Re: B&S push mower Carb issue

02/12/2015 4:03 AM

Phew....for a minute there I thought you were having a go at my native accent.

He is from south of the border possibly from Yorkshire/Lancashire, maybe Dell could put me right on that one.

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#6

Re: B&S push mower Carb issue

02/10/2015 11:23 PM

I would be looking for an air leak in the fuel delivery tube, this is a common problem and even a very small leak will stop them cold. Check especially for deteriorating hoses and broken plastic fittings in the pipe system.

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#7
In reply to #6

Re: B&S push mower Carb issue

02/11/2015 1:39 AM

After re-reading the OP I would just about guarantee that this is indeed an air leak in the fuel delivery hose. The comment that the primer bulb still doesn't work is a good clue.

The primer bulb is simply a device which sucks fuel through the carburetor from the tank and sends it back to the tank in order to have fresh fuel at the carburetor for a rapid start, it doesn't normally put fuel into the throat of the carby or in any other way aid starting.

So three possibilities exist -

1. The carby gaskets are leaking allowing air in that way, but as you say you have replaced them, this is a remote possibility.

2. The outlet valve in the primer is faulty, thus allowing air to be drawn from the tank - the bulb won't prime and the carby won't draw fuel.

3. There is a leak in the line from the tank to the carby, thus allowing air to be drawn in.

If there is a leak in the fuel line going to the carby, then the primer will be sucking air and not fuel, and the bulb will not fill.

If it was a blockage in the fuel delivery line, then the bulb would remain depressed due to the negative pressure on its inlet.

If it was a blockage on the return to tank line, then the bulb would be hard to depress due to positive pressure on its outlet.

One test would be to pressurise the tank by blowing into it and seeing where the fuel is escaping. You can do this safely by plugging the filler hole with a rag, inserting a bit of garden hose through the plug, and blowing through that, keep the tube clear of the fuel to avert blow-back when you stop.

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#13
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Re: B&S push mower Carb issue

02/11/2015 11:41 AM

Hi Spades, just to make thing a bit more complicated: there is no hose between the tank and the carb: both are screwed togetheter.

The housing of the priming bulb has what I believe to be 2 valves... and I am afraid one may not be working: will have to check that again (this time wearing glasses!)

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#15
In reply to #13

Re: B&S push mower Carb issue

02/11/2015 5:47 PM

If the primer return valve is not sealing, then the carby will draw air back from the tank via that valve, but only if the fuel level in the tank is below the return orifice.

Try filling the tank completely so that the carby can't draw air that way, and try again.

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#11
In reply to #6

Re: B&S push mower Carb issue

02/11/2015 11:17 AM

I did: no air leaks, nor deteriorated hose.... (it´s so frustrating!)

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#8

Re: B&S push mower Carb issue

02/11/2015 6:24 AM

Don't know your exact B&S model, but the principle of implementations that carb lies higher than the fuel tank, is the use of intake vacuum peaks and dips (per combustion cycle that is) to pulse a membrane, the other side of which is the varying space of a gasoline pump. Pump also involves TWO one-way valves, usually implemented by little "tongues" of the same membrane material, that seal two tiny carb bores. So your problem narrows down to one of the above. I would start with those valves and also double check for intake air-leaks and/or clogged passages on carb body. S.M.

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#9

Re: B&S push mower Carb issue

02/11/2015 7:57 AM

I think you can buy a new one of these attached to a mower body for around $100 US.

They are becoming like Microwave ovens: it is cheaper to buy a new one than to spend time cleaning the one you have...

Good Luck fixing it though, but if you do have a hole, there is probably another one to show up as soon as you fix this one. I would suggest giving this engine to the kid down the street that likes to work on stuff and go buy a new mower or engine.

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#17
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Re: B&S push mower Carb issue

02/11/2015 7:14 PM

You are right when you say that these engines are becoming like microwaves.... but mine is less than 2 years old, and I resist the idea of getting a new one, cause it will have the same problem in two years or so! ... and I will not give the engine to the kid down the street, cause he has been painting grafittis all over the neighbourhood :-(

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#12

Re: B&S Push Mower Carb Issue

02/11/2015 11:23 AM

See comment #9...LOL!

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#18

Re: B&S Push Mower Carb Issue

02/11/2015 10:40 PM

Everyone has pretty much nailed it down with good recommendations.

Due to the level of Ethanol in gasoline, you may have to replace all plastic and rubber components that come in contact with the gas. Ethanol is most likely melting the plastic parts and deteriorating the rubber gaskets.

A friend of mine who runs a Lawnscaping business told me to use the 360 Marine grade Sta-Bil added to the gasoline, to help prevent or minimize parts degradation. So far, after 4 years of using the product I no longer have had engine problems with my lawn tractor, push mower, weedwackers, chainsaws, and what have you. Before I stated using it, I spent a small fortune having my machines repaired every year!

Don't use the original grade Sta-bil. It will not help you!

http://www.sta-bil360marine.com/

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#19
In reply to #18

Re: B&S Push Mower Carb Issue

02/11/2015 10:52 PM

Most manufacturers of small engines recommend against using Ethanol inclusive fuels in their equipment.

I for one only use regular unleaded in all small 2 stroke and 4 stroke motors including my 150 hp 4 stroke outboard.

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#26
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Re: B&S Push Mower Carb Issue

02/12/2015 8:04 AM

The problem in Florida is that it was mandated that all gas contain at least 10% ethanol.

The problem not only impacted lawn and garden equipment, but it also badly hit the marine market, too, which is big in Florida.

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#27
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Re: B&S Push Mower Carb Issue

02/12/2015 8:22 AM

AH -

There are around 500 pure gas (ethanol free) stations in Florida... I have a Mobil gas station by me that have a dedicated pump for that.. it is just kind of cost more per gallon vs. the premium type...

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#28
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Re: B&S Push Mower Carb Issue

02/12/2015 9:06 AM

Pure-gas.org is a good site to locate ethanol-free gas near you. It's accurate for the couple of towns that I know of. They list 556 locations in Florida.

I haven't had much problem with ethanol in my larger engines, but it really affects small two-strokers, so I buy ethanol-free for them all now. I've told friends that don't want to fool with it to buy the $5-6/quart pre-mixed stuff if they have small yards.

Off-topic BTW, if 10% ethanol is 'mandated', why is ethanol-free still available?

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#32
In reply to #26

Re: B&S Push Mower Carb Issue

02/12/2015 11:06 AM

How many deaths at sea per year attribuble to loss of engine while out of harbor, and ethanol in the fuel? Can anyone say law-suit?

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#38
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Re: B&S Push Mower Carb Issue

02/14/2015 6:28 AM

Go diesel....safer anyway....

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#49
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Re: B&S Push Mower Carb Issue

02/17/2015 1:18 AM

A diesel push mower?? It would be impossible to push it with the heavy block required to handle the compression ratio necessary to ignite the fuel. Then the heat would lead to grass fires.... and the oil needed to lubricate the cylinders,... and the cooling system needed to...then there is the starting compression problem for a manual pull start.... the complications are obvious! Get a $10,000 Kubota tractor with a diesel just to mow one lawn? Hire that kid down the street to mow with his dad's mower and you are way ahead.

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#50
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Re: B&S Push Mower Carb Issue

02/17/2015 5:49 AM

I feel with a modern design, it could be possible and maybe even lighter than a petrol engined one. I looked around, just for a few minutes only, and found a 2HP tiny outboard motor using a diesel engine.

See what you think, but remember, 2 HP is not much, but usually a diesel will have a lot more torque! and use a lot less fuel!!

If they can do it, so can many other engineering firms.....

http://www.alibaba.com/product-detail/2hp-2-stroke-outboard-motor-RMC_60169105093.html?s=p

Where you can find this tiny Diesel engine in an outboard!!!:-

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#51
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Re: B&S Push Mower Carb Issue

02/17/2015 10:07 AM

The specs sheet says "gasoline" for fuel type, but the title name says diesel. The fuel tanks are red and the fuel tank looks like it's made for gas (vented). Who knows?

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#52
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Re: B&S Push Mower Carb Issue

02/17/2015 11:28 AM

Your comments do not hold water (pun intended!) as you appear to forget or not know, the name of Diesel in many countries!

In France its called "Gazole" or directly translated = "Gas-oil" in English.......

In Italy its called "gasolio".

In Spain its called "gasóleo".

Its actually one of the good reasons to call it petrol and not gas as you are less likely to make a mistake..... France petrol = Essence!!

Many Americans (and some others I bet!!) over the last 100 years or so, till they changed the spouts of the pumps, put Diesel in a "petrol" hire car in places like France and some other countries.....after all, it was obviously called "Gas"!!!

Diesel tanks are also vented on simple setups, otherwise they might collapse as diesel pumps are often very good at pulling a vacuum......as well as high pressures for the injectors.....assuming no charcoal filter filter of course on an outboard...I may be wrong and there is one!!

Funnily enough, modern petrol (maybe Diesel too!) cars are NOT allowed to have ventilated caps as the tank must draw its air via a charcoal pack, to prevent hydrocarbon emissions from car fuel tanks, especially on warm days....

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#33
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Re: B&S Push Mower Carb Issue

02/12/2015 2:54 PM

Thankfully the public outcry when Australian authorities tried that was great enough to prevent it - at least so far.

Some outlets - I won't state their name but it starts with S has 5 letters and ends with L - don't stock normal unleaded here, so we just don't deal with them.

Incidentrally, we're still paying $1.37 per litre ($5.19/US gal) for E10 where I live.

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#31
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Re: B&S Push Mower Carb Issue

02/12/2015 11:04 AM

For the last several years, I have been using StaBil products also as a fuel additive. For winter storage, and first starts in the spring I use another product in a spray bottle, called Blast-R, it will absolutely unstick parts (or use it for lay-up to prevent this), and assures an easy start with the first or second rope pull.

I finally had to give up (before this) on the carb to my Stihl string trimmer. Ethanol stretched the diaphragm, and make it useless, among other problems. Local mower shop installed new carb for way less than cost of new string trimmer, so it's all good.

The new carb has better diaphragm in it made just for high ethanol content gasoline.

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#20

Re: B&S Push Mower Carb Issue

02/11/2015 11:38 PM

I'm not an expert in small engines, but common sense tells me that ethanol is probably used in most gasoline engines and Briggs and Stratton has included provisions to prevent the fuel lines from deteriorating. My cursory research shows that E10 is OK, but E15 may be problematic. The people who sell stabilizer say it's bad and I should buy their wares...

I personally use the standard E10 in my B&S engine and have never had any problems. The deck usually rots out, or a big rock takes it out before I ever have engine trouble. I change the oil once year. blow out the air filter, etc... never used stabilizer. I don't even drain the fuel as usually suggested. I know if I did the better maintenance the $200.00 mower might last longer than the 6 years my current mower is on. Maybe I'm lucky or the OP has the higher E15 stuff in his local.

Please comment if this thinking is somehow skewed....

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#21
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Re: B&S Push Mower Carb Issue

02/12/2015 12:05 AM

Apart from the effect on O-rings etc, which can be overcome, another major problem with Ethanol blends is that Ethanol is hygroscopic.

Where a fuel tank is left idle (such as in a lawnmower etc.) the Ethanol will take moisture from the air, it will then accumulate in the bottom of the tank and cause corrosion and/or cause the engine to malfunction due to ingesting that moisture.

This moisture attracting property becomes a major issue with marine engines for obvious reasons.

Those links that you provided are pretty damning of Ethanol blends in small motors - why take the chance for a few cents saved?

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#22
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Re: B&S Push Mower Carb Issue

02/12/2015 12:25 AM

Spades, Thanks for the reply..

I agree. I should use stabilizer and empty the tank when sitting idle for long periods, but I haven't had any issues personally. (touch wood)

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#23

Re: B&S Push Mower Carb Issue

02/12/2015 12:34 AM

You say its less than two years old? Should be set up for blended fuel. I would call (or visit) the repair-person in the area and see if that is a common problem. Could be they know just what the problem is. If not, any advice from them may narrow down the problem. I used to have dozens of mowers and parts in the yard. I will look around in the morning and see what I can find.

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#25

Re: B&S Push Mower Carb Issue

02/12/2015 6:37 AM

Lots of good ideas, but one you may have missed is:- is the vent hole in the petrol/gas tank blocked?

Simply try starting it with the cap a turn loose.....

My money is on the two one way valves that prevent fuel returning to the tank though, at least one of them is probably not working, probably on the tank side one.

I hope you get it working soon.

Maybe after the fix, an extra filter in the tank, I used bits of old women's stockings as a filter media....cheap and it catches the big stuff! Two pieces and it starts to catch the small stuff as well....

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#35
In reply to #25

Re: B&S Push Mower Carb Issue

02/12/2015 6:11 PM

Hi Andy, I have checked the vent on the cap, and it is (unfortunately ;-) ok . Earlier today I visited a B&S representative. He recommended to change the membrane and gasket again and also told me to detach the gasoline intake tube (which has a filter at the tip) from the base of the carb. As this part seems to be glued to the carb, nobody removes it for fear of breaking it (it requires a twist and simultaneous pull). For this reason everybody just blows the clogs up and down along the tube with compressed air.... (like I did) The other trick he mentioned is to gently push a little SS ball valve located at the base of the priming bulb, cause it gets stuck with gums that build up in the fuel, preventing it to work properly. This will be my homework for the weekend. As soon as I have done it, will post my experience....

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#36
In reply to #35

Re: B&S Push Mower Carb Issue

02/12/2015 6:21 PM

I would bet you fix it this weekend.....best of luck!

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#34

Re: B&S Push Mower Carb Issue

02/12/2015 4:42 PM

Another solution to avoid the problem in the future is to run Avgas or aviation gasoline. Planes sit sometimes for extended periods and as a result of that they have additives that keep the fuel from "going bad". It does cost more but in the long run it is worth it to eliminate the frustration of fighting the problem of seasonal use of mowers, garden tiller, weed whacker, chipper shredder, followed by the dreaded snow blower. I was told by the dealer that I should go out and start everything once a month but I just can't bring myself to wade the foot of snow to the shed to run a mower every month.

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#37

Re: B&S Push Mower Carb Issue

02/13/2015 7:20 AM

It sounds like you are having fun, I got to thinking "what in the world is he doing messing with his lawn mower this time of year? maybe this is a hoax," serves you right for living in a beautiful place such as Buenos Aires.

I won't find out what is wrong with my lawn mower for another 4-1/2 months minimally.

Referring back to my original solution in post #9: Have you checked the spark plug? Is it in good working condition? Then here is your solution:

Take out the spark plug.

Throw away your current engine.

Buy a new engine.

Replace the new spark plug with the one you currently have.

That may be enough to relieve your mind in that you have fixed your engine problem and you can now once again sleep in peace in beautiful Buenos Aires.

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#40
In reply to #37

Re: B&S Push Mower Carb Issue

02/14/2015 8:20 PM

Hi, Thanks for your words about Buenos Aires! :-) In regard to your idea of keeping the spark plug and throwing away the engine... I also evaluated such a possibility, but what if the OLD spark plug is the faulty part ???? Pls check my post below on how I got it back to life! PS: If you happen to come back again, give me a call, and I´ll invite you to mow the lawn with my newly repaired machine!!!!

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#39

Re: B&S Push Mower Carb Issue

02/14/2015 1:05 PM

Check the fuel line from tank to carb. If the clamps need tightened or the flexible fuel line is kinked it will leak air and ruin the siphon. Also clean the fuel tank screen in case the intake is plugged.

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#41

Re: B&S Push Mower Carb Issue

02/14/2015 8:52 PM

The beast finally surrendered, and as Galileo Galilei Said: "Eppur si move" following the tips the B&S service guy gave me, I disassembled the carb again (this time with my glasses on!) and focused my attention on the tube that aspirates gasoline from the tank (on the right in the pic) http://outdoorpowerinfo.com/repairs/images/briggs_carb_790206/_diaphragm.JPG (sorry, but I´m using my Mac and don´t know how to post images) This tube has to be removed (pull while twisting it) and thoroughly cleaned: I sprayed 3M carb cleaner and it looked fine... but when drying t with compressed air, a whitish film appeared on it (gasoline residues), repeating the procedure was of no help, as this filter continued clogged. A toothbrush was of no help either. After figuring out what chemical might be of help, I decided to go for a Paint Stripper, which removed all the gum from the screen in less than 10 minutes! The rest was just sewing and singing: after placing a new diaphragm and gasket and putting all together, the engine started with no problems and worked really fine! Thanks for your cooperation! Fall (your spring) is coming soon, so I will be back for advise when the chainsaw quits!

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#42
In reply to #41

Re: B&S Push Mower Carb Issue

02/15/2015 10:12 AM

it´s actually "mUove"

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#43
In reply to #42

Re: B&S Push Mower Carb Issue

02/15/2015 12:42 PM

Well done....

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#45
In reply to #43

Re: B&S Push Mower Carb Issue

02/15/2015 9:09 PM

Vielen Dank ! (Thank you!)

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#44
In reply to #41

Re: B&S Push Mower Carb Issue

02/15/2015 5:31 PM

Thanks for the feedback! My recommendation on your chainsaw and other 2 cycle tools: unless you know that you'll be using it again within 1 or 2 weeks, pour the gas out of the tool back into the gas can and then start the engine and let it run at low or medium speed until it quits.

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#46
In reply to #44

Re: B&S Push Mower Carb Issue

02/15/2015 9:22 PM

Hi Bigg! I used to have a 2 cycle outboard on my boat, and always did what you recommend.... but last fall I forgot running the chain saw´s carb dry; so I have the feeling I soon will have to deal with another clogged carb! (but It´s still soon to get concerned about!)

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#47

Re: B&S Push Mower Carb Issue

02/15/2015 10:29 PM

Good to hear it, bravo. As for the chainsaw, mine is electric, so I can use it in the shop without smokin the place up. An I dont miss pulling the cord to start it, not one bit.

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#48
In reply to #47

Re: B&S Push Mower Carb Issue

02/15/2015 11:21 PM

I have the feeling the next one I´ll buy will be electric too ;-)

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