# Honda GX120 Won't Start



## Keepin It Reel (Feb 20, 2019)

On my JD 220SL, the GX120 engine will not start. A few days ago the engine would run with the choke on and die the moment I turned it off. I immediately thought the jets were clogged in the carb so I removed the bowl and 2 jets inside the stem as well as the jet under the throttle adjustment screw. After I got everything back together it wouldn't run at all.

I've changed multiple carbs over the years and cleaned jets and am sure everything went back together correctly. The odd thing is when I put gas down into the intake it still won't run. I checked the spark plug and its firing when held agasint the body of the mower but I swapped it anyways. Still no luck.

I also checked the oil levels and all is well. I have no idea what's going on. Any insight would be appreciated.


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## JML (Jul 26, 2021)

There are a lot of small gaskets that can tear easily. Honestly, you can buy a new carb on Amazon for $15, will be there tomorrow, and start first pull. Do that and save yourself the headache.


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## Keepin It Reel (Feb 20, 2019)

JML said:


> There are a lot of small gaskets that can tear easily. Honestly, you can buy a new carb on Amazon for $15, will be there tomorrow, and start first pull. Do that and save yourself the headache.


The motor should still run briefly with gas in the intake even if the carb is bad but it won't. That's why I'm not sure it's a carb issue.


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## Bmossin (May 31, 2018)

Crazy flooded? Any chance just really weak spark where you might need a coil?


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## JML (Jul 26, 2021)

possible the fuel line/filter are clogged? Meaning that running on choke (less air) then when extra air is added, it's too lean (clogged).
On/off switch disconnected (open circuit)?


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## Keepin It Reel (Feb 20, 2019)

JML said:


> possible the fuel line/filter are clogged? Meaning that running on choke (less air) then when extra air is added, it's too lean (clogged).
> On/off switch disconnected (open circuit)?


When I turn the switch on I get spark from the plug when held against the frame.


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## Guest (11 mo ago)

got spark- points to fuel delivery issue...try some direct starter fluid in carb/intake. does it have a fuel petcock by chance?


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## Keepin It Reel (Feb 20, 2019)

Nixnix42 said:


> got spark- points to fuel delivery issue...try some direct starter fluid in carb/intake. does it have a fuel petcock by chance?


I put straight gas into the intake and it wouldn't start


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## Mightyquinn (Jan 31, 2017)

Not sure if this will help but it has some good information.










Here is a link to a better image

Honda Carb Check Sheet


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## GreenLand (May 23, 2019)

Given @Keepin It Reel sounds like he knows what he's doing the next thing I would check is compression. If all gaskets are good compression is the next issue to check. Gaskets and low comp will show in no starts. Especially with the choke closed as that will draw more velocity/ cfm into the engine.


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## bigpetzi (Sep 7, 2021)

Have you checked the oil level and/or the oil level switch?


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## Keepin It Reel (Feb 20, 2019)

bigpetzi said:


> Have you checked the oil level and/or the oil level switch?


Yep not that either.

Wonder if it's timing related


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## GreenLand (May 23, 2019)

https://youtu.be/hID3btLVYj8

https://youtu.be/QVxsd_UD0TQ


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## bernstem (Jan 16, 2018)

Some other resources: 
GX120 shop manual.
The JD220e uses a GX120 and theshop manual is very thorough.

I'm not much of a small engine mechanic, but with good spark, good airflow, and fuel delivery to the cylinder I think next steps are valves and compression. I know you probably checked, but could there be something like a gasket piece in the intake somewhere? Greenland's linked videos are pretty good. There are dozens of videos on GX120 repair and maintenance which is nice if you don't like those.


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## MasterMech (Sep 24, 2017)

Choke it like normal and pull it over 5-6x. Pull the plug. Is it wet?

If not and we're sure there's fuel available (via priming?):

Pop the valve cover and make sure everything is ok under there. Not unheard of for a valve to stick and drop the pushrod.

If yes, then troubleshoot ignition, followed by compression.

Visual spark at atmospheric pressures does not necessarily equate to good spark installed in the combustion chamber. If you are seeing bright, blue spark, that's a good sign. Weaker, yellow spark, or spark that requires you to shade the plug to see it should be considered suspect. Might replace the plug if there's any doubt to it's condition too. Deposits on a plug can cause the ignition voltage to bleed off rather than jump the gap under combustion pressures.


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## Keepin It Reel (Feb 20, 2019)

MasterMech said:


> Choke it like normal and pull it over 5-6x. Pull the plug. Is it wet?
> 
> If not and we're sure there's fuel available (via priming?):
> 
> ...


I pulled the valve cover today and pulled the starter cord and both valves freely moved up and down. I then pulled the flywheel to check the key and it was fine as well. The spark plug was just changed and it's nice and blue.


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## Automate (Aug 14, 2020)

Keepin It Reel said:


> Nixnix42 said:
> 
> 
> > got spark- points to fuel delivery issue...try some direct starter fluid in carb/intake. does it have a fuel petcock by chance?
> ...


Try starter fluid. You may have some bad gas and its hard to get the right air/fuel ratio just pouring gas in.

Also, pull the spark plug and turn the engine over and make sure you have some compression in spark plug hole.


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## Keepin It Reel (Feb 20, 2019)

Automate said:


> Keepin It Reel said:
> 
> 
> > Nixnix42 said:
> ...


I've tried starter fluid as well plus the gas works fine in my Honda push mower .


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## GreenLand (May 23, 2019)

Compression testers are free at auto parts stores. You rent and get your money back.


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## Automate (Aug 14, 2020)

I was given a lawnmower that exhibited the same kind of problem. Pulled the sparkplug, stuck my finger in the sparkplug hole, turned the engine and nothing. Engine had broke rod without throwing it through the crankcase.


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## LienandGreenLawn (Mar 5, 2019)

Any update on fix? I have a 220b with exact same issues. Spark is good. Cleaned carb. Plenty of fuel to carb. Starts with starter fluid then dies a few seconds later.


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## jimbeckel (May 27, 2018)

I just repaired my Honda gx120, it had started fine and ran. A few weeks later, same problem as you, put a compression tester on it and it read 60psi. I inspected the valves and found severe carbon deposits on the valves and top of the piston. I cleaned all of the parts in an ultrasonic cleaner, reassembled everything and the engine fired back up. Low compression will prevent the engine from starting.


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## LienandGreenLawn (Mar 5, 2019)

jimbeckel said:


> I just repaired my Honda gx120, it had started fine and ran. A few weeks later, same problem as you, put a compression tester on it and it read 60psi. I inspected the valves and found severe carbon deposits on the valves and top of the piston. I cleaned all of the parts in an ultrasonic cleaner, reassembled everything and the engine fired back up. Low compression will prevent the engine from starting.


one thing I haven't checked! I need to pick up a compression gauge. so my wife's toothbrush is ultrasonic, is that what you mean? :lol: harbor freight has these for decently cheap. like 70 bucks. what is normal compression on these motors?

-ML


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## LienandGreenLawn (Mar 5, 2019)

https://www.youtube.com/watch?v=QVxsd_UD0TQ 
here's a good video for how to properly check compression on these honda gx engines.

Edit: Posted previously, whoops.


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## jimbeckel (May 27, 2018)

LienandGreenLawn said:


> jimbeckel said:
> 
> 
> > I just repaired my Honda gx120, it had started fine and ran. A few weeks later, same problem as you, put a compression tester on it and it read 60psi. I inspected the valves and found severe carbon deposits on the valves and top of the piston. I cleaned all of the parts in an ultrasonic cleaner, reassembled everything and the engine fired back up. Low compression will prevent the engine from starting.
> ...


I redid two mowers from Weeks, both with the GX120 so I had one good engine and another with the bad engine. The good mower I believe had about 110 psi and the non starter was 60. If you have over 100 psi then I would rule out engine compression.


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## MasterMech (Sep 24, 2017)

LienandGreenLawn said:


> Any update on fix? I have a 220b with exact same issues. Spark is good. Cleaned carb. Plenty of fuel to carb. Starts with starter fluid then dies a few seconds later.


Carburetor related. If it fires on starting fluid, then all is well except for fuel delivery.

Side note: I really try to avoid using starting fluid (ether) on small engines. For diagnostics, carburetor cleaner (in aerosol cans) works just as good and is much safer for the engine.


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