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I have a 12A-18M7002 MTD Yard Man Self Propelled 173cc OHV mower.

This model has the Kohler engine.

It is difficult to start but will eventually start and run terribly.

It spits and sputters.

I have:

Changed the spark plug
Drained the gas, cleaned out the tank and used new gas
Took the original carburetor off and cleaned all the passages.
Swapped the carburetor for a known working one.
Checked the muffler to ensure it wasn't clogged.

The automatic choke works as I see it adjusting the carburetor as the motor tries to stabilize itself.

The coil must have spark as the engine does start, but runs terribly.

I don't want to throw a new carburetor or coil at it without knowing what is wrong.

There were a couple of times that it actually started easily and ran fine, but the symptoms have recurred.

Any ideas?

Thanks

http://www.mtdproducts.com/equipmen...Code=03&modelNumber=12A-18M7002&serialNumber=

See pages 18 & 25 in engine operators manual for troubleshooting chart & fuel filter location. Carburetors are different, specific carburetor part number for specific engine model number to run properly. You may want to purchase a carburetor rebuild kit by looking in parts manual for your engine model parts list.

mechanic mark said:

http://www.mtdproducts.com/equipmen...Code=03&modelNumber=12A-18M7002&serialNumber=

See pages 18 & 25 in engine operators manual for troubleshooting chart & fuel filter location. Carburetors are different, specific carburetor part number for specific engine model number to run properly. You may want to purchase a carburetor rebuild kit by looking in parts manual for your engine model parts list.

Click to expand...

Thanks, I did check the troubleshooting chart and even removed the fuel filter to ensure that gas was flowing. So far no change.

I suspect the carburetor is defective, I have had it apart 2x but there must be an issue with it.

Am going to order a new carburetor.

peabodyn said:

Thanks, I did check the troubleshooting chart and even removed the fuel filter to ensure that gas was flowing. So far no change.

I suspect the carburetor is defective, I have had it apart 2x but there must be an issue with it.

Am going to order a new carburetor.

Click to expand...

I know this might be a long shot, but have you checked the air filter? I have a MTD Black push mower (MTD engine) and it has been running rough as well. I've cleaned the filter, but will not know when this may have fixed the issue, until my next grass cut.

Hopefully this can steer you some direction...

Lawnaholic said:

I know this might be a long shot, but have you checked the air filter? I have a MTD Black push mower (MTD engine) and it has been running rough as well. I've cleaned the filter, but will not know when this may have fixed the issue, until my next grass cut.

Hopefully this can steer you some direction...

Click to expand...

Actually, the air filter is clean - good idea though.

I did see a video on Youtube that suggested adjusting the idle speed and potentially drilling the low idle jet to a slightly larger diameter.

I believe that the prior owner of this mower messed with it and sold it because he couldn't fix it.

I got it real cheap - now I'm paying for it in time and potentially parts.

peabodyn said:

Actually, the air filter is clean - good idea though.

I did see a video on Youtube that suggested adjusting the idle speed and potentially drilling the low idle jet to a slightly larger diameter.

I believe that the prior owner of this mower messed with it and sold it because he couldn't fix it.

I got it real cheap - now I'm paying for it in time and potentially parts.

Click to expand...

I adjusted my idle screw to allow the mower to run a little louder, but it kept my mower from dying every 15 seconds. I'm hoping the air filter is clean enough so I can adjust it back.

Update here when you find a fix!

--Nick

Is there a diaphragm that you could replace?
Ethanol Gas has been a cause of the degradation of many, many of these.
I have replaced about a dozen of the diaphragms in various yard motors in the last year.

Advise as able.
Thanks.

hdsport said:

Is there a diaphragm that you could replace?
Ethanol Gas has been a cause of the degradation of many, many of these.
I have replaced about a dozen of the diaphragms in various yard motors in the last year.

Advise as able.
Thanks.

Click to expand...

Don't think so. I've checked the schematic diagram and there isn't a diaphragm.

have you checked the ignition switch? ( whatever eletrical contacts that move when you pull the bail-bar down) it might be the problem... you seem to have eliminated the possibility of fuel issue very well and hat the few plces an ignition problem could occur with a cold engine i think.. other possibiility is an air leak ( head gasket, intake manifold gaskets)

when it does start.. does it smoke black smoke?

I've found out that if I manipulate the lever on the carb (closest to the engine), I can get the mower to run fine.

I suspect the prior owner messed with the carb and put it back together the wrong way.

I have a similar carb and will compare the two to see if I can see what's wrong.

What about fuel filter? Old fuel filter is no good.

misha84 said:

What about fuel filter? Old fuel filter is no good.

Click to expand...

The mower will run fine if I keep the throttle linkage pushed to the front of the mower.

What does this mean?

Is there something that is set up incorrectly?

Do I need to get a new carburetor?

I hope the pictures have attached.

Thanks

Did you read the manual that Mark pointed you to ?
The thing you have the clamp on is the govenor arm and that is attached to the throttle butterfly.
The choke is at the front of the carb.
I choke you by shoving someting in your mouth not your bum :laughing:
If that is moving back & forth then it is doing what it is intended to do.
If the engine is surging, revving up, dieing then reving up again you are not getting enough fuel into the engine for the volume of air.
So ither there is a restriction in the carburettor preventing the fuel from flowing through.
or
The float level is too low so the wind passing by can not suck enough up
or
there is an air leak somewhere between the emulsion tube and the inlet valve.

bertsmobile1 said:

Did you read the manual that Mark pointed you to ?
The thing you have the clamp on is the govenor arm and that is attached to the throttle butterfly.
The choke is at the front of the carb.
I choke you by shoving someting in your mouth not your bum :laughing:
If that is moving back & forth then it is doing what it is intended to do.
If the engine is surging, revving up, dieing then reving up again you are not getting enough fuel into the engine for the volume of air.
So ither there is a restriction in the carburettor preventing the fuel from flowing through.
or
The float level is too low so the wind passing by can not suck enough up
or
there is an air leak somewhere between the emulsion tube and the inlet valve.

Click to expand...

When I took the carb apart the first time, I noticed that someone had used some sealant on the bowl gasket that was degraded by gasoline.

I suspect pieces of the sealant were sucked up into the internal passages of the carb and that I have not been able to clean them out, despite taking it apart and cleaning it out.

It looks like it's time for a replacement carb.

Yes, silicon has a place, behind an electrified fence topped with razor wire and all who access it should do a two year course after a qualifing IQ examination.
OTOH I make a lot of money cleaning t out from where it never should have been used.

Check for air leaks by putting some WD 40 or similar in a TRIGGER SPRAY BOTTLE and while the engine is running liberally spray it around the carb and engine manifold.
If the engine reacts then you have an air leak.
Check the float level as per the instruction in the manual Mark directed you to.
Clean the carb FUEL Passageways as per the same manual then adjust the govenor also according to the manual Mark directed you to.
When you have finished install the carb with nice new gaskets and a new float bowl gasket.
Start the engine
I it still acts naughty, hold the govenor rod flat out .
If the engine runs fine then check the govenor settings again.
If the engine misses and sounds like it is running out of gas then replace or rebuild the carb.
It is a bit of a moot point now days as the rebuild kits are usually 1/2 the price of a new carb.

I put the new carb on the mower today.

The mower still runs poorly.

Hard to start and spits and stumbles and has low RPM's.

Does the governor need to be adjusted? If so, how?

Suggestion?

Thanks

i think youd need to be 110% sure your using the proper holes for linkage from governor to carb etc.. not nessarily the same ones you removed it from ( in case previous mech fudged it) and to ensure your not seeing any air leaks down stream ( carb to manifold, manifold to head.. head to block..) is the valve lash in spec?? are you 110% sure the problem IS fuel delivery? could it be something in the ignition grounding out and causing misfires?

i wish i had that eureka moment for you.. i know these issues are troublesome to track down

I took a propane torch and without lighting the gas, held it close to the carb, and manifold to see if it was sucking air.

There was no change in the idle, so I don't think its sucking air.

There is only one hole for the throttle linkage so I don't think that is the issue.

If I manually hold the throttle open I can get it to run ok.

I don't think the issue is ignition as it will start and run OK if I hold the throttle open.

I suspect the governor needs adjustment, I will get a tachometer so I can set the idle speed correctly.

I wouldn't know where to begin to check the valve lash.

It's frustrating..... I bought this mower 'cause it was cheap and thought it would be an easy fix.

Thanks for your input!

its possible your dealing with a broken governor mechanism inside the engine... only one hole in the carb for linkage huh.. is it the proper linkage?? is it bent??

when its running, take that unlit propane torch and falow the intake tract with it... head gasket too.. any change in engine RPM means your onto something here

Will try again with the unlit propane torch.

Replacement carb is identical to original, no concern that the linkage is wrong.

Haven't had the time (or inclination) to play around with the mower. Will make time next week.

Thanks for the response.

The unlit propane torch is a waste of time unless you are trying to generate a big bang.
It needs to be a liquid, WD 40 , Metholated spirits ( a tad dangerous ) even water will do but propane is silly.

bertsmobile1 said:

The unlit propane torch is a waste of time unless you are trying to generate a big bang.
It needs to be a liquid, WD 40 , Metholated spirits ( a tad dangerous ) even water will do but propane is silly.

Click to expand...

OK. I will try again with WD40.

Thanks

Picked this project up again after the long fall and winter.

I changed how the spring was holding the butterfly on the carburetor by using a piece of wire to make a loop and attaching the spring to that.

Unfortunately, the manual did not have a picture of how it should be, but its works so I am satisfied.

This keeps the butterfly closed when starting.

After replacing the pull rope (it broke after dozens of pulls trying to start the mower), it started right up.

The rear wheel self propel is much better than any of the front wheel ones I've used.

Thanks to all for the ideas and help!

Probably going to give this mower to my oldest son, who just bought a house.

Best to all