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2023/02/12 14:46:06
just4fn

GX390 Kicks back

I picked up a Honda GX390 so I don't have any history.  The pull start was missing so I put one on that I had.  It wouldn't start so I sprayed starter fluid down the carb.  It kicked back hard and took the starter rope out of my hand.  I tried several times and yep it kicks back.  I removed the valve cover and watched the exhaust valve.  Yes it has the small dip for compression release,  The valves were a little lose so I tightened them to specs.  .018 exhaust and .015 intake.  Put it back together and it still kicked back. I removed the valve cover again and valves were still correctly adjusted. I did notice the exhaust rocker does not go down as far as the intake.  Do you know if both lobes on the camshaft have the same lift?  What else should I look for that would create the kick back?  Thanks for the help!!!!
11 comments Leave a comment
Conrad Sigona
Check whether the key cut in the flywheel is aligned with the key cut in the shaft, that is, whether the key is present and intact. It might seem unlikely that that's your problem, but it's easy enough to check.
 
I have myself had trouble with kick-back when starting larger single cylinder motors if there's nothing attached, for instance, no pulley, no blade, nothing to give it momentum, and I started it too slowly. I'm getting old and can no longer quickly pull the cord on the larger engines. That is, when the motor sits by itself on the work bench, my shoulder will hurt from the kick-back, but when it's attached to whatever it's running, it starts nicely. My solution is to ask help from a young man (my Amish neighbors are helpful in this respect), who can pull the cord fast enough that there is no kick-back. It's usually an Amish motor that I'm working on anyway!
2023/02/12 14:59:20
just4fn
Thanks for the suggestion!  I can look at the key and see.  I'm afraid a little to pull super hard for fear I might break my fingers. I broke the starter rope that I had to repair. I do use a glove now when trying to pull it. I did remove the pressure washer pump so I could start it without have to run any water.  Maybe I need the drag.  I don't know. 
2023/02/12 15:13:12
SRTsFZ6
Besides / in addition to checking the flywheel key, you can get an idea if it's out of time by checking when the flywheel magnet is near the coil..
 
It should be very close when at TDC on the compression stroke. (You can watch the valves open / close in ref to finding TDC)
 
Re the valve, does it appear to be closing fully, just not pushing open as much as the intake?
2023/02/12 18:57:37
just4fn
It appears it's fully closing, just not pushing down as far. 
2023/02/12 23:34:45
just4fn
I took the front cover off and the woodruff key looks fine. 
2023/02/18 15:27:30
SRTsFZ6
You can see BOTH the crank notch and the flywheel notch themselves, correct?
 
If one isn't visible, you have to pull the flywheel to check
2023/02/19 07:20:57
just4fn
Here's a picture of the front of the flywheel:
 
 
2023/02/19 13:56:00
just4fn
I put it on top dead center and found the magnet at 12:00.  Is this correct?
2023/02/19 14:24:17
just4fn
SRTsFZ6
You can see BOTH the crank notch and the flywheel notch themselves, correct?
 
If one isn't visible, you have to pull the flywheel to check


I tried to smack the flywheel but it would not come off.  Afraid to hit it harder.  Getting a flywheel puller may be challenging 
2023/02/19 14:25:30
SRTsFZ6
The magnet on the flywheel should be close to the COIL when at TDC, ( not sure if that's 12:00)..
 
Obviously you can see the key in your pic but can't see if it's clocked/inserted in the crank (it could be sheared). 
 
Often, if you put a pry tool between the block (a "safe spot) and flywheel and put pressure up on the flywheel, 
you can smack the crank shaft end and the flywheel will pop off.  Protect the threads with leaving the nut on, just e even with the top edge of the crank...  
 
.
2023/02/27 08:19:25
just4fn
I ended up replacing the camshaft even though it was working fine and it looked good.  All is good now. 
2023/07/01 17:16:36

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