Honda GX390 issues: blowing white smoke / will not turn off

Herkdriver

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Hello everyone. I am having some issues with a Honda GX390. This motor is on Trail Wagon UTV that I recently acquired for free. The motor had not run for about four years and had been blowing white smoke when it was parked.

Although I am pretty good with DIY things, I’ll state up front that I am not a mechanic. This seems like a good project for my son and I to do together, so I would like to try and fix this engine (if possible) and learn something at the same time.

I was able to get the engine running.

Currently, there are two issues I am aware of:
  1. As I expected, the engine is still blowing white smoke out of the exhaust. I suspect that it has a blown head gasket and/or the piston rings need to be changed. I checked the compression and it consistently indicates 105-110 psi.
  2. The engine starts with the keyed ignition, but does not stop running when the key is turned OFF. I have to choke it so make it stop. The headlights extinguish when the key is turned to the OFF position, so I know that at least some part of the ignition switch is working.
I am planning to remove the head and check for a bad head gasket. I have a copy of the shop manual and have watched a lot of Youtube videos. Any advice on either of these issues would be much appreciated.

Thanks,
Lance
 

bertsmobile1

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Remove the blower housing and locate the coils.
There should be a thin wire attached to each on them.
That is a kill wire which should be open circuit when the engine is running and goes to ground to turn the engine off
The key switch should have tiny letters cast into the back of it
G = Ground
B = battery
M = Magneto
S = Start
A = Auxillary ( Alternator )
L = Lights
Off = G + M
On = B + A
START = B + S + A
On some off will also connect A to G which turns the alternator into a motor to stop the engine quickly when turned off.
To check the rings you need to do a leak down test.
As this is a family bonding exercise I would suggest that you get the youngen to make one , plenty of You tube vids on that.
Then forever that will be the magic tool they made.
also suggest you make a pop bottle soda blaster to clean the engine with.

Thus you have also taught your family how to make what they don't have and opening the wallet is not the only solution.
 

Herkdriver

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Bertsmobile1,

Thanks for your reply. Your explanation about the ignition switch and coils is very useful. I’ll definitely check all that out. Having my son make a leak down tester is a great idea! I’ll do a little research and pick out a good design for one. I‘m not familiar with a pop bottle soda blaster. I’ll look into that as well.

You've given me some good homework assignments. I totally agree with you about making what you can at home. I am sure we will both learn a lot from this project.

Thanks again!
 
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