# Lawn Mower starts for two seconds then dies



## guaps

I have a Yard Machines by MTD lawn mower. I pump the primer 5 times, and it starts every time, but just as the engine is reaching normal rpms, the engine dies. It only runs for 1-2 seconds then dies.

I changed the air filter and put a new plug in it, and it still has the same problem.

I changed the gas and oil. Then I took off the carb and cleaned it with carb cleaner and blew it all out with the compressor. It still has the same problem.

It doesn't sound like the engine is missing.

Any ideas? I've spent a couple days after work now trying to fix this, and I'm at the end of my understanding.

Thanks!
jeff


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## Yoyizit

guaps said:


> I pump the primer 5 times, and it starts every time, but just as the engine is reaching normal rpms, the engine dies. It only runs for 1-2 seconds then dies.


It sounds like you are running on the gas in the float bowl, if it has a float bowl. 
There is a fuel line obstruction upstream of the primer bulb?


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## guaps

Yoyizit said:


> It sounds like you are running on the gas in the float bowl, if it has a float bowl.
> There is a fuel line obstruction upstream of the primer bulb?


It does have a float, but everything seems to be fine upstream from the primer bulb. I checked where the fuel leaves the tank and it flows fine. Then I checked where it enters the carb, and it was flowing fine. Then I unscrewed the fuel from the bottom of the bowl, and gas flowed out easily. Gas is definitely getting to the bowl. I sprayed carb cleaner through all the parts/holes/tubes inside the carb and everything seemed clear. Am I missing something?


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## nap

is this 2 stroke or 4 stroke engine?


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## Yoyizit

Electrical problem/ignition/ignition timing? 

I don't know if these engines have a timing advance, either vacuum or centrifugal or both.


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## guaps

nap said:


> is this 2 stroke or 4 stroke engine?


I'm 99% sure it's 4 stroke. I don't mix the gas/oil, so that means 4 stroke, right? There is a cap where I fill the oil, and it has a small dipstick to check oil level. So I'm pretty sure that all means it's 4 stroke.



Yoyizit said:


> Electrical problem/ignition/ignition timing?
> 
> I don't know if these engines have a timing advance, either vacuum or centrifugal or both.


I don't know hardly anything about electrical nor ignition systems. If I knew what to look for, I might be able to figure it out, but I don't even know where to start to look for problems there. Any suggestions?


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## nap

guaps said:


> I'm 99% sure it's 4 stroke. I don't mix the gas/oil, so that means 4 stroke, right? There is a cap where I fill the oil, and it has a small dipstick to check oil level. So I'm pretty sure that all means it's 4 stroke.


no gas oil mix makes it a 4 stroke. So much for the idea I had.


still sounds like a fuel problem though. What is happening just isn't typical of an ignition problem.

does it have a manual choke? If so, have you tried changing the choke setting after it starts?


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## Yoyizit

guaps said:


> I don't know hardly anything about electrical nor ignition systems. If I knew what to look for, I might be able to figure it out, but I don't even know where to start to look for problems there. Any suggestions?


You'll need a schematic. There might be a generic one online.
I'm thinking now that the engine vibrations open up a loose connection somewhere in the ignition circuitry. The engine stops, the connection closes again, and the cycle repeats.

If it is a fuel problem, what quantity of fuel is burned in 2 seconds? If it's not the gas in the float bowl, what other volume of fuel is being used up this quickly? 
If anyone can post what running time they get from a full fuel tank and the tank volume, we can figure out what fraction of a cubic inch you are looking for. Maybe an air bubble forms somewhere because some air bleed opening somewhere is clogged.


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## guaps

Yoyizit said:


> If it is a fuel problem, what quantity of fuel is burned in 2 seconds? If it's not the gas in the float bowl, what other volume of fuel is being used up this quickly?
> If anyone can post what running time they get from a full fuel tank and the tank volume, we can figure out what fraction of a cubic inch you are looking for. Maybe an air bubble forms somewhere because some air bleed opening somewhere is clogged.


You obviously understand this better than I do, but my guess would be there is more fuel in the float bowl that could burn in the short time this thing runs. Again though, that's a guess.

Could there be some kind of kill switch or governor that could be kicking in and cutting the engine? Where would something like that be located if there was one?


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## Yoyizit

guaps said:


> there is more fuel in the float bowl that could burn in the short time this thing runs.


The governor should even out the speed with varying demands on the engine, rather than kill it.

Post what technical info you have on this machine and we can do some informed troubleshooting.

Loosen the gas cap and see if it still stalls.


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## guaps

Yoyizit said:


> The governor should even out the speed with varying demands on the engine, rather than kill it.
> 
> Post what technical info you have on this machine and we can do some informed troubleshooting.
> 
> Loosen the gas cap and see if it still stalls.


I tried loosening the gas cap (I even took it off completely), but no luck. Great idea though. 

When you say to "post technical info I have", what are you referring to? specs for the lawn mower from the user manual?

Thanks for sticking with me on this. I really appreciate the help.


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## Stillwerkin

Same thing happened to me. 
-I kept the thing going by taking off the the air filter and kept pushing the primer when it started to falter. 
-I also put my hand over the air inlet, mostly covering it. This creates an artificial choke(increasing the internal vaccum inside the carburator) which sucks more fuel in. 
-When the rpms were high, I'd briefly cover the inlet completely to try to pull the blockage through. 
-After it warmed up(remember a hot engine requires less fuel) it now seems to run ok. I'm thinking(in my case) there was sediment in the fuel system which was sticking in the needle valve(which regulates the level of fuel in the float bowl). 
-The blockage seems to have flushed through, and it starts good when warm now. Either that, or the fuel line has a break and is letting air in. 

If there was too much gas, your's would smoke heavily before croaking. 

It it fires at all, then the ignition system should be working, unless it has a seperate circuit specifically for running-mode. New plugs/oil and clean connections are always good.


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## Stillwerkin

I'm not sure about how the new 4-stroke mowers work, but I've heard the gas-cap test is useful for automobiles with evaporative emisions systems with computer controlled fuel curves.

Think:
1. Air(usually a given but an engine is basically an air pump)
2. Fuel
3. Spark
4. Timing


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## Yoyizit

Forgot; check for particles in the gas tank, flush if necessary.

Yes, whatever tech. info on this that you can beg, borrow or steal, online or off. Sometimes I look in library books on small engine repair for ideas. Occasionally a book will mention some detail that the others omitted.


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## DangerMouse

Yoyizit said:


> Forgot; check for particles in the gas tank, flush if necessary.


Good idea.... also, how old is the gas? Did you put in fresh?

DM


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## guaps

Stillwerkin said:


> Same thing happened to me.
> -I kept the thing going by taking off the the air filter and kept pushing the primer when it started to falter.
> -I also ...


Thanks for this. I'll try it tonight when I get home from work and report back...



DangerMouse said:


> Good idea.... also, how old is the gas? Did you put in fresh?
> DM


It's brand new gas. I changed the gas when I changed the oil.



Yoyizit said:


> Yes, whatever tech. info on this that you can beg, borrow or steal, online or off. Sometimes I look in library books on small engine repair for ideas. Occasionally a book will mention some detail that the others omitted.


I'll go dig around and post what I can find.


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## DAdams982

guaps said:


> Thanks for this. I'll try it tonight when I get home from work and report back...
> 
> 
> 
> It's brand new gas. I changed the gas when I changed the oil.
> 
> 
> 
> I'll go dig around and post what I can find.


Not exactly the same engine, but I had the same problem with an old 4 wheeler that was 4 cycle. A friend borrowed it and mixed the gas like it was a 2 cycle, and never changed the oil and rode the hell out of it... burnt the rings and had to replace them.


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## Yoyizit

You can check that you have ignition by putting a spark gap in series with your spark plug.

If you use another spark plug for this gap, close it down to 0.01" or so, about the thickness of 2 sheets of copy paper. 
To withstand engine vibrations you will have to mechanically secure the extra plug to the engine housing with insulating material that can stand a few KV. Dry wood comes to mind.
As long as you see a spark in the tiny gap you are getting ignition.

Alternately use clear tubing, epoxy and parts from other spark plugs to make your visible spark gap. This will be smaller and lighter so it may stand on its own. You could use a 6-32 machine screw sharpened to a point to mate with the screw-on connector on top of the plug, or use paper clip wire [which is springy]. The current through this gadget is only a few mA.

An old neon timing light may also work, but the ignition voltage for a small engine may to be low for this.

I've never had to make one of these gaps, not yet. . .


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## piste

fuel pump...


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## tbone2004

I would have suggested the fuel cap like another person already said. I know you said you blew it all out of the carb, but years back my father and I had similar problem and it wasn't until we took a very fine piece of wire and cleaned out each hole on the carb that the gallons of gumout had not cleaned apparently...after that it was fine. Sounds to me it is choking itself or the fuel is getting in the carb, but not getting out. Please post again when resolved - many of us will encounter this no doubt at some point....


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## bernieb

Have mower outside, no kids around, fire extinguisher handy and have a friend spray gas with a windex bottle into intake with carb removed and see if it'll stay running. Sounds like you have a stuck gas inlet needle in carb that needs changing.


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## BigJohn1980

I have had this same prob before on a push mower I had. I thought it might be the primer bulb as it was worn out, I thought it might have been sucking air through a crack on the bulb. Turns out that it wasn't the prob. I wound up having to replace the whole carb. I went through a lot of the same stuff you have to no avail. After putting the new carb on it ran like a new one. Jonathon


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## zacker

how long has it sat with gas in it? did you drain the tank then run it dry before you stored it last winter? sounds like a dirty carb.. i know you cleaned it so if its not still dirty it may need rebuilding.. try replacing the float, gasket, needle valve and the tiny seat in the hole the needle valve sits in.... Bring the carb to the shop with you and have them remove the old needle valve seat, its easy for them to blow it out with a compressor. 
Then, Use something about the same diameter of the gasket to push the new one down fully into the seat or the needle valve wont work and gas will pour out of the carb. 
I had a woodchipper that would only run on starting fluid, i took off the carb, cleaned it and it still didnt work so i rebuilt it and added an inline gas filter, that did the trick...also, do yourself a solid, when you remove the carb and install the inline filter, also install an inline gas shut off valve, makes working on the carb and draining the tank much more of a pleasent experience. When you get it running, go buy a can of sea foam and add some to your gas... just to keep things clean and fresh.


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## bernieb

You got that right Zacker on using Seafoam, and a great post I might say. This new gas we have, it really gums up the carbs not only in lawn mowers but very destructuve with outboard motors. When gas sits like in a lawn mower or a outboard things start happening after several months and you wind up with "skin" like substance in fuel lines ,carbs and fuel pumps. On my outboard I had a stuck electric fuel pump and a new one cost 800 bucks plus labor for replacement, but I found out by reversing the 12v polarity and 40 trys it broke loose, and soaking in Seafoam overnight of course. There is a blue liquid bought from Napa (can't think of the name) that prevents the breakdown of gas over the winter that I now use.


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## piste

I'd speculate that your carb is totally fine based on the comment that after pumping the primer bulb that it starts EVERY time and runs for a few seconds and dies...which is the time it takes to burn the gas that you provided it via the pumping of the bulb and then it stalls simpy cuz it's not getting any more gas. If there were issues with the carb I would think it wouldn't start and run and die so consistently ...albeit very briefly. So...if it has a fuel pump I'd go there first and foremost. If no fuel pump...check/replace the fuel line between the tank and primer bulb for obstructions.

So it's been a while now....how is it going? What have you tried lately? Inquiring minds want to know.


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## zacker

I may be wrong here but if the primer bulb is gassing it up, then how could the gas line be blocked?? or does your machine have a seperate line for the primer bulb? plus useing the bulb could be filling the bowl with gas where as the carb isnt getting the suction on its own to take in gas by itsself. I still say dirty carb, rebuild it..hey for $10.00 its worth it even if it turns out to be something else. I dont believe these small engins even have a feul pump.. do they??


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## piste

zacker said:


> I may be wrong here but if the primer bulb is gassing it up, then how could the gas line be blocked?? or does your machine have a seperate line for the primer bulb? plus useing the bulb could be filling the bowl with gas where as the carb isnt getting the suction on its own to take in gas by itsself. I still say dirty carb, rebuild it..hey for $10.00 its worth it even if it turns out to be something else. I dont believe these small engins even have a feul pump.. do they??


Many of these small engines don't have fuel pump...but I believe some do. I have a lawn edger that had exact same symptoms of the OP....was fixed under warranty and was told it was the fuel pump. It COULD potentially be getting gassed up by the primer bulb but not normal running if the pressure created by the primer bulb is enough to overcome any blockage but normal operation is not enough. That's a stretch but possible. To me...the issue is related to whatever mechanism is responsible for providing fuel during normal engine running. The primer bulb operation is an initial substitute for that mechanism to get things started. An easy test would be start er up and keep pressing the primer bulb...see if she continues to run.


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## BigJohn1980

piste said:


> Many of these small engines don't have fuel pump...but I believe some do. I have a lawn edger that had exact same symptoms of the OP....was fixed under warranty and was told it was the fuel pump. It COULD potentially be getting gassed up by the primer bulb but not normal running if the pressure created by the primer bulb is enough to overcome any blockage but normal operation is not enough. That's a stretch but possible. To me...the issue is related to whatever mechanism is responsible for providing fuel during normal engine running. The primer bulb operation is an initial substitute for that mechanism to get things started. An easy test would be start er up and keep pressing the primer bulb...see if she continues to run.


Thats kinda the way mine was. If I held the primer about half way in it wuld run,but as soon as I let go it would shut off. I wound up cleaning the carb a couple times to no avail. Wound up getting a carb from my grandfather that was the same type, put it on and she ran like a new one. Not really sure what the real prob was,but do know it was in the carb. Jonathon


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## zacker

the gas eats at all the elastomers in the fuel system.. the lines can rot and leak (happened to a chainsaw and a leaf blower) and also, esp. in two stroke engins like weed wackers, the carbs have a diaphragm instead of floats and it can get soft and not work and youll get the same thing.. it will run on a prime or starting fluid but not on its own.. rebuild the carb, be sure to run a wire in each hole and spray alot of cleaner throught them too, you can soak it all in sea foam for a day or two also..but for the $10 or $15 you spend, its well worth it!


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## guaps

It's been a while since I updated you all on my progress - I have been out of town for the last week. I have been reading some of the new replys, and there are more good ideas I need to go try. The last thing I tried was Stillwerkin suggestion of creating a choke with my hand over the air intake. Unfortunately, it didn't help. 

I'll start through the list of new suggestions tomorrow and over the weekend. At this point, I'm determined to get this thing running. I'll be sure to post the solution WHEN (not if) we find one.

Thanks again for all your help!


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## DangerMouse

Personally, I appreciate it as well. I have a mower out back that I'd like to fix that does the same #@!#@[email protected]#ing thing, so I hope these great guys figure it out with you! Po)

DM


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## AlDaja

I just had the same thing happen to me today (run for a second or two then die). After checking and cleaning the fuel line, I discovered after taking the plug out that the end of it (connector) had unscrewed a little; probably from the vibration of the mower. I screwed it tight and the mower started right up and stayed running.


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## guaps

I never did figure out the source of this problem. I spent weeks trying to figure it out. (I didn't try AlDaja's solution though) Eventually, I gave it away on Craigslist to a helicopter mechanic who said he was 100% he could fix it. I hope he did...


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## moondawg

guaps said:


> I never did figure out the source of this problem. I spent weeks trying to figure it out. (I didn't try AlDaja's solution though) Eventually, I gave it away on Craigslist to a helicopter mechanic who said he was 100% he could fix it. I hope he did...



He can, but he has to turn them upside down so that the blade is on the top...:jester:


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## Majikterror

*Solved.*

I did everything with cleaning the carb, also I did what some say not to do. I pulled the fuel feed line and blew my air nozzle through it. I then did it from the opposite direction. Then I blew out the fuel tank and the air filter cover. Changed the filter and put it the same old gas. Runs like brand new it just took a couple extra pulls to get things flowing again.

I posted this since I couldn't find a solution and hope that this may help the next guy like me who is too proud to bring something to a repair shop before he has taking the whole the thing apart and tried everything.

Toodles
:thumbup:


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## dps1948

*Primer bulb dose not work*

I have a briggs engine (lawnmower) 1999 that only runs if you feed the carb by dripping fuel into the carb via a straw,as long as you keep fuel going in it runs. Now I bought a carb kit from Lowe's and matched up the design of the old gaskets to the new and they are identical. I bought a new bulb too, The primer does not get fuel up to the bulb??? Now what do I do??? All passageways have been cleaned with carb cleaner and blown out with shop air.


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## blueracer66

*lawnmower fix*

-starts, but will not keep running.....after watching three U-Tube how to's and reading five how to's--I got my mower to start. For a novice, let me tell you go straight for the carburetor and clean the jets with the "loaf bread" tie wrap and spray into the carburetor over and over with the carburetor cleaner....BINGO:thumbsup:


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