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-   -   Lawn Mower starts for two seconds then dies (http://www.diychatroom.com/f16/lawn-mower-starts-two-seconds-then-dies-75467/)

guaps 07-05-2010 06:58 PM

Lawn Mower starts for two seconds then dies
 
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

Yoyizit 07-05-2010 07:38 PM

Quote:

Originally Posted by guaps (Post 465669)
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?

guaps 07-05-2010 08:24 PM

Quote:

Originally Posted by Yoyizit (Post 465688)
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?

nap 07-05-2010 08:29 PM

is this 2 stroke or 4 stroke engine?

Yoyizit 07-05-2010 08:41 PM

Electrical problem/ignition/ignition timing?

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

guaps 07-06-2010 11:29 AM

Quote:

Originally Posted by nap (Post 465722)
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.

Quote:

Originally Posted by Yoyizit (Post 465739)
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?

nap 07-06-2010 11:44 AM

Quote:

Originally Posted by guaps (Post 465978)
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?

Yoyizit 07-06-2010 01:42 PM

Quote:

Originally Posted by guaps (Post 465978)
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.

guaps 07-06-2010 05:34 PM

Quote:

Originally Posted by Yoyizit (Post 466039)
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?

Yoyizit 07-06-2010 09:04 PM

Quote:

Originally Posted by guaps (Post 466146)
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.

guaps 07-06-2010 10:22 PM

Quote:

Originally Posted by Yoyizit (Post 466244)
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.

Stillwerkin 07-06-2010 11:56 PM

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.

Stillwerkin 07-07-2010 12:01 AM

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

Yoyizit 07-07-2010 08:36 AM

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.

DangerMouse 07-07-2010 08:42 AM

Quote:

Originally Posted by Yoyizit (Post 466385)
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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