Need help with a Honda engine GX390

[okrobie]

First off, this is an engine that I bought at a junkyard for $20, so I’m trying to keep my expectations at a realistic level. Actually, it’s a generator. The compression felt good so I bought it. It came without a carburetor or a gas tank but otherwise looked good. I had a gas tank and I purchased the hew carburetor from Amazon.

At this point, I have fuel and fire. The carburetor is getting gas because I dropped the bowl and it was full. I pulled the plug and grounded the threads with an alligator clip lead and saw spark the plug. I have a compression tester but can’t hold it and pull the cord simultaneously. (I did try) I don’t know much about the valves so I’ll need help in that area. Thanks, Jim

 

[bertsmobile1]

Start from basics
Squirt a SMALL amount of carb cleaned down the plug hole & give the carb a pull
Engine does not go bang = remove the blower housing and check the flywheel key
Engine goes bang out the carb = bad timing or inlet not properly closed
Check the key as above & the valve lash
Engine goes bang out the exhaust = same as above
Engine goes bang normally = timing OK & valves closing fully

next do the same down the carb throat
Engine goes Bang , bang , bang a few times = valves are OK and carb is bad .

 

[StarTech]

GX390K1 Valve clearances
INTAKE 0.15 +/- 0.02mm ( 0.006 +/- 0.001in )
EXHAUST 0.20 +/- 0.02mm ( 0.008 +/- 0.001in )

Also while adjusting the valve check for the ACR bump of one of them. It been a couple years since my last GX390 valve adjust so I don't remember it is the IN or EX valve. Don't see many Honda engines here. But I know if the ACR is broken the engine can give up one heck of kickback through the recoil rope. One strained my waist several years ago.

 

[Scrubcadet10]

ACR bump is on the Exhaust on my gx390.

 

[nobot]

Have you already attached the fuel tank and carburetor? Have you tried starting it? Did you do the initial adjustment on the pilot screw (screw all the way in, then loosen 3 complete turns)? Do you have a float gauge, and did you check that the float height is set to 13.2mm (0.52 in)?

The first link below is a very detailed removal, cleaning and installation guide for the GX160, but should apply to all GX series engines. The second link is a video that corresponds to that guide. I recommend watching/reading because they detail each gasket, seal and spacer, some of which could have been lost when the old carb was removed.

GX160 Carburetor Service

Honda GX160 Carburetor Service Directions: Use a Honda GX160 single cylinder horizontal engine to complete the following worksheet. There is a box before each numbered step. Check it off after completing each step. Stop at all places marked “Instructors Check '' and have the instructor s...

docs.google.com

This video details the setting up the governor linkage:

What does the engine oil look like? Any reason to suspect internal engine damage? If not, I would install the carb and fuel tank, check the adjustments, see if it runs, and then worry about the internals if there is a problem.

Engine RPM adjustment:

If it doesn't run, check these:

flywheel key (good point, Bert)

Ignition timing:

Valve adjustment (also check this if it's hard to crank):

If there's no power, do a compression test

 

[okrobie]

Start from basics
Squirt a SMALL amount of carb cleaned down the plug hole & give the carb a pull
Engine does not go bang = remove the blower housing and check the flywheel key

Thanks Bert, I stopped at step one so I'm back to the flywheel.

 

[okrobie]

Have you already attached the fuel tank and carburetor? Have you tried starting it? Did you do the initial adjustment on the pilot screw (screw all the way in, then loosen 3 complete turns)? Do you have a float gauge, and did you check that the float height is set to 13.2mm (0.52 in)?

Thanks nobot, yes, the carb and fuel tank are installed. I have some other parts that I didn't mention yet because like Bert said I'm trying to stick to basics. After I get it running, I'll introduce the fact that I have a starter motor and A natural gas/propane kit that I want to install. But that's further down the road.

Thanks for those videos. I really need them. They are right where my need is.

 

[okrobie]

ACR bump is on the Exhaust on my gx390.

Thanks cadet and StarTech, but I don't know what an ACR bump is.