Honda GX390 will not run.

[bertsmobile1]

Well it has to be the carb or the throttle/governor set up
When the engine is at rest the governor should have the throttle wide open and as soon as the engine starts to run it should CLOSE down the throttle .
Remove the throttle link to the carb at the governor end & start the engine
See if you can work the throttle by hand.
Next silly question is do you have the linkages on the right butterfly ?
throttle is closest to the engine and choke is closest to the air filter.
Not sure if you can cross them over on your engine but I have had some come in with the control rods connected to the wrong butterflys so the governor turned the choke on.
And on some the throttle &/or choke shafts have 2 hook up points so they can be either pushed open or pulled open and again I have seen them set up backwards.

 

[Scrubcadet10]

Most GX390s have the plastic handle that actuates the choke, right above the fuel cutoff.

 

[bertsmobile1]

Most GX390s have the plastic handle that actuates the choke, right above the fuel cutoff.

Depends if it has the remote control kit fitted which is why the "not sure" was put in there .
Same with the throttle
Some have 2 holes so they can be hooked up backwards and some only one hole.

The last option would be an obstruction in the muffler causing the engine to suffocate on it's own exhaust.

Mr Wilson mentioned he replace the piston which you can do without touching the cam so I would expect that the valve timing is correct .
He also says he has checked the valve lash so unless he is adjusting it on the exhaust stroke one would assume that is correct.
And I am fairly sure there is not enough adjustment in the rockers to get clearance on the exhaust rocker at TDC exhaust stroke .

 

[Jwilson22071]

have you tried using an alternate fuel tank/supply?

I pulled the current tank off a running unit but let me try another one. I'm willing to try anything now. Thanks

 

[Jwilson22071]

Depends if it has the remote control kit fitted which is why the "not sure" was put in there .
Same with the throttle
Some have 2 holes so they can be hooked up backwards and some only one hole.

The last option would be an obstruction in the muffler causing the engine to suffocate on it's own exhaust.

Mr Wilson mentioned he replace the piston which you can do without touching the cam so I would expect that the valve timing is correct .
He also says he has checked the valve lash so unless he is adjusting it on the exhaust stroke one would assume that is correct.
And I am fairly sure there is not enough adjustment in the rockers to get clearance on the exhaust rocker at TDC exhaust stroke .

I did take the engine all the way down when I replaced the rings just to make sure there was no other damage. I really watched when I put the balance rod and the cam back in to line up the timing marks. ( Maybe I need to check again) Have not checked compression but I know it tries to blow my thumb off of the hole on the compression stroke. Valves are set at .006/.008. Its got a brand new head and valves. Tonight I found that if I hold my hand over the intake it tries to stay running with the choke closed but as soon as I move my hand it dies. I pulled the head again tonight to make sure I haven't messed up the head gasket. It still looks new. Hard to diagnose when it won't run long enough to even grab the choke lever. This engine originally came in for a broken governor gear and that's when we found the bad rings. I've even swapped governors again. Starts really easy on choke but pulled kind hard and will not start when the choke is open. That's why I'm starting to lean towards maybe I got the cam off or something . I will check the exhaust out again tomorrow. Thanks to everyone for the help. I know its something dumb but I will find it.

 

[jlee4363]

I have repaired a few hondas with your problem and the fix was simple. I cleaned a carb few times on first as it would crank then die like it was fuel starved did some forum research and read that the ngk plugs are not made in japan anymore and are prone to premature failure and as yours is doin crank and die, sure enough i changed out the plug and it ran perfect. Since then i have diagnosed a few more. Not sure if this was coincidence or what but the honda engine w ngk plugs were all on woodsplitters. G'luck

 

[Ranamow]

I don't know if anyone mentioned this. I have seen new insulators with cracks in them. Check it closely, or use the old one. You're definitely getting air from somewhere.

 

[Jwilson22071]

Ok here is a update- pulled the cover off double checked the cam timing which was good. Tried to start it a couple of times and it yanked the rope out if my hand. Swapped out flywheel and key. Original key might be bent... have to measure and see. Ran the valves again which were spot on. Still won't run. Unhooked fuel tank and hooked my remote test tank up. No change. Swapped exhaust. No change. Swapped to a 3rd carburetor- now I could hold it against idle and it would run for a bit. Noticed fuel spitting out of carb where the airbox should be- shut the gas off and pulled the rope and it started then ran out of gas. Opened gas back up and it fired right up but, the rpms went thru the roof. So I held the throttle partly shut and let it run for a little bit. Ran out of time to mess with it so when I get back on it I will put the airbox and air filter back on and see if I can figure out why the governor seems to not be working. When I set it with the throttle rod pushed to the right counterclockwise so I was at WOT and turned the governor shaft counterclockwise as far as I could since the governor gear it in the back cover. Will dabble some more tonight or in the morning.

 

[Jwilson22071]

Oh yeah swapped out the insulator and gasket it too before the carb swap .... no change. Thank you guys for all the help!!!! Don't know if I'm there yet but at least it runs somewhat now.

 

[Jwilson22071]

So.... I have the held all the way to the right if you are facing the engine at WOT. I loosen the jam nut and turn the governor shaft counterclockwise as far as it can go. Tighten jam nut back down. Start engine up and it revs to the moon. I can push the throttle shaft shut it will idle down but if I let it go it revs right back up. The manual throttle handle is in the idle position and there is zero tension on the governor spring. Any ideas? Governor worked just fine before I tore the engine down.