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Discussion Forum

Re: GX390?

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RGMartin

10-16-2012 04:32:20
173.189.141.138



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Quoting Removed, click Modern View to see

The low oil switch is a Oil level sensor, not pressure. If that is the issue, rocking side to side will usually get it going. You could also try bypassing the switch if you keep an eye on your oil level.

390s are a big engine to pull by hand.




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George Marsh

10-16-2012 04:47:31
50.104.232.125



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 Re: GX390? in reply to RGMartin, 10-16-2012 04:32:20  
RGMartin,
For some reason, I thought the sensor measured oil pressure. I have a 20 hp kohler that I'm sure it's sensor measures pressure, because every time I change oil and filter, it takes a few more cranks before the engine makes a spark. Once I goofed, pulled the choke to start the enging after changing oil, About 10 cranks later the spark arrived and shot fire out the muffler. One BIG BANG.

Because the 390 doesn't have an oil filter, you may be right. What tells the sensor there is the presence of oil if it doesn't use pressure?

You're right, it takes a lot to crank a 390. My right arm is still hurting.
George

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Billy Shafer

10-16-2012 07:50:42
173.184.79.154



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 Re: GX390? in reply to George Marsh, 10-16-2012 04:47:31  
The 390 has a splash lube system. No oil pump so no pressure. The level switch is the only oil protection it has. The Honda switch is more reliable than most.You can unplug it and see if it makes starting any better.But I don't think that is your problem.

How many hours on the engine,is compression good, valves set properly.

If you are like me. The main problem is age. Ain't as young as we used to be.

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George Marsh

10-16-2012 14:30:00
50.104.232.125



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 Re: GX390? in reply to Billy Shafer, 10-16-2012 07:50:42  
Billy,
Checked valve clearance. Both were close. Tightened the exhaust perhaps .001-.002 inches. Nothing major. However, I did notice what Honda called using the exhaust valve as a decompression valve. When I rolled the motor over slowly, the intake valve open and closed. On the compression stroke, the exhaust valve opened a small amount and just breifly. Then on the exhaust stroke, the exhaust valve opened even more and stayed open for a longer time.

How does Honda do this? I'm guessing it has 2 lobs on the exhaust cam. Or is there another way to get the exhaust valve to open briefly on the compression stroke just while you are starting the engine? Wouldn't this send a small amount of fuel/air mix out the exhaust before there is a spark?

Do other small engines do the same thing making it very critical to keep the exhaust valve clearance spot on the money?

Thanks,
George

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Billy Shafer

10-16-2012 07:57:34
173.184.79.154



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 Re: GX390? in reply to Billy Shafer, 10-16-2012 07:50:42  
Almost forgot. Valves

Intake 0.15 MM
Exhaust 0.20 MM



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George Marsh

10-16-2012 10:09:46
64.12.116.141



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 Re: GX390? in reply to Billy Shafer, 10-16-2012 07:57:34  
Billy, thanks for the info.

Bought pressure washer used. It has no hour meter. As for compression, YES, that's what makes so hard to start. Sometimes it fires too early and pulls the starter out of my hand.

Going to check valve clearance and put a thinner oil in it.

George



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Billy Shafer

10-16-2012 15:21:47
173.184.79.154



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 Re: GX390? in reply to George Marsh, 10-16-2012 10:09:46  
George. Those are cold settings. The cam lobe controls compression release. No other way that I know of. Briggs has the same system.I should have the 390 manual somewhere around my nice clean office.I will check.



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George Marsh

10-16-2012 19:36:47
50.104.232.125



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 Re: GX390? in reply to Billy Shafer, 10-16-2012 15:21:47  
Billy,
I adjusted the valves when cold. Exhaust was only about .002 in out. I did notice the exhaust valve opening a little on the compression stroke? Does the cam do that? Are there 2 lobs on the cam?
George



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JDseller

10-17-2012 03:33:23
208.126.196.144



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 Re: GX390? in reply to George Marsh, 10-16-2012 19:36:47  
The cam has a weight that is on a lever. That lever turns a small shaft that has an eccentric on the end of it. That eccentric sticks out into the exhaust lobe of the crankshaft. The weight it held one way with a spring. So at low speeds the eccentric will open the exhaust valve a little at crank speeds. When the engine hits and comes up to running speed the weight over comes the spring pressure. Then the eccentric is flush with the cam lobe and no longer hits the exhaust valve.

Have you tried a new spark plug. I have a JD pressure washer that has a Honda motor on it. If it starts hard it usually is the spark plug not firing right under compression. Also are you able to crank it good and fast??? As my Dad has gotten older he can't pull the rope fast enought for small engines to start correctly. He complains about this one or that one not starting correctly. Me or my sons can just give it a good yank and the engine starts fine.

I have actually mounted a few snow blower motors on some of the things he uses with a small gas engine on them. The snow blower motors have 110 volt electric start on them. So he can just plug in the cord and hit the button and away he goes.

One of his motors was the same model as one used on snow blowers. I was able to change the flywheel to one that would use the electric starter.

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George Marsh

10-17-2012 04:35:03
50.104.232.125



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 Re: GX390? in reply to JDseller, 10-17-2012 03:33:23  
JDseller,
I'm looking for a flywheel and starter. I think my problem is I'm getting old. 3 days later my arm and sholder is still hurting from pulling on the starter.

May buy myself a new pressure washer with a starter for Christmas.

My 6.5 briggs on a pressure washer is a dream to start, but the gismo that adds soap and bleach is broken. It's built into the pump. I would have to buy a new pump to fix the problem. I need to do something, still have 3 properties to clean.

George

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