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2022/12/28 22:05:25
K Ryan

Honda GX120 Wont start/run

Hi Guys,
New here, so hi to everyone. 
I have a Honda GX120 on a cement mixer that I am having issues with.  It ran fine about 9 months ago when i last use it but now, nothing not even a kick.  I first checked the spark and it was weak, so i replaced the starter/coli, which improved the spark, but it still would not start.  I have tried spraying starting agent and fuel, directly into the air intake to no avail.  Not even a kick. This lead me to believe it was a compression issue, so I checked - compression 90 psi (measured with a new gauge).   I also checked the valve clearances, which were within Honda specs.  For good measure I also rebuilt the Carburetor.     What has me perplexed is that it is showing compression of 90 psi but wont even give one kick.  Can anyone offer any further advice before I remove the head to investigate?  Thanks 
4 comments Leave a comment
SRTsFZ6
Compression is a bit low...
 
Try putting 2-3 teaspoons of engine oil down the cylinder and rotate to distribute. 
 
Put the spark plug back in and try to start normally.. 
 
The oil raises the compression some with the rings.  The rings my be carboned up/stuck some.  Once started (if not real bad) it'll often work.
 
Soaking the combustion chamber with Seafoam to break up deposits wouldn't hurt either..
 
 
.
2022/12/29 08:24:38
K Ryan
Thanks for the reply and advice SRTsFZ6. I did what you recommended.  I got it compression up to 125 psi and eventually got it to start.  I ran it for a bit at nearly full throttle to burn off oil and carbon, then eased it back to about half throttle. After a few minutes , it started to run roughly, then cut out.  Tried starting again and it did, once, after a few pulls, continued to run roughly and cut out. I could not get it started again.  Checked compression again and was back to 90psi.  I think I will either need to rebuild or transplant a Chinese replacement engine. I will do some research on rebuild kits.
2022/12/30 00:29:03
SRTsFZ6
You'd just need new rings, side cover gasket and head gasket.. 
 
Before buying parts, pull the rings and measure them in the bore(end gap). 
 
 
I'd rather have that Honda than a Chinese knock off...
 
Please post back how it goes... 
 
 
2022/12/30 17:42:10
K Ryan
I would definitely also prefer the Honda.  I finally got to pull the piston and have a look.  All looked good (in my limited knowledge).  There was no cylinder scoring or lipping. The piston looked like new, except for a little soft carbon deposit (probably from the oil I put into the cylinder burning off) which wiped off.  The end clearance on the ring was 0.025 inch or 0.635mm, which I believe is in spec.  This made me wonder if it was a head gasket issue.  The head bolts all seemed to be equally torqued down, when I took it apart but there is a little section of the block that is not as smooth as the rest but I haven't cleaned it up yet and it could just be the imprint of the old head gasket.  the cylinder liner seemed to have a good seal.  I have ordered new rings and gaskets.  They are 2 weeks away. Hopefully when I rebuild it my problems are solved.  I will let you know how it goes.  Thanks for the help so far.  
2023/01/03 05:12:16

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