Honda GX390 strange problem - Snowblower Forum : Snow Blower Forums
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post #1 of 38 Old 02-05-2018, 08:41 PM Thread Starter
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Honda GX390 strange problem

Hi
I repowered my snowblower with a near brand new Honda GX390 last fall

It start easily everytime, runs correctly from idle to full throttle (3600 RPM). When the motor has to deliver more power, the governor open the carburator butterfly and the motor bogs sputters but work. It is doing the same thing when it is at full throttle (3600 RPM) and I open the carburator butterfly manually with the governor rod. It doesn't rev more but sputters.

Here what I tried to get rid of this problem.

- Cleaned the carb
- Tried another carb
- Replaced the spark plug
- Adjusted the valves

With all these things done, the problem is still there. The only thing I suspect now is a faulty coil. Could it be the problem ?

Thanks
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post #2 of 38 Old 02-05-2018, 08:55 PM
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I go back to a carb problem, or a fuel delivery problem, restriction, fuel inlet float valve.

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post #3 of 38 Old 02-05-2018, 09:04 PM
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Did you allow the engine to fully warm up before testing? With newer engines that run leaner, you might have to let it warm up for 10 minutes or more before it'll run properly with the choke fully off.

Also have you checked for air leaks between the carb and the engine? Or possibly even a missing gasket?

Other than that, although the symptoms you describe 90% of the time are fuel problems, it's possible it's an ignition issue. Maybe see if you can find a used magneto (so you're not spending too much $ if it doesn't work) and toss it on there.

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post #4 of 38 Old 02-05-2018, 09:06 PM Thread Starter
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There is no problem with fuel supply

When I unscrew the drain screw on the float bowl, gas is flowing freely when the fuel valve is open.
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post #5 of 38 Old 02-05-2018, 09:18 PM Thread Starter
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Quote:
Originally Posted by ELaw View Post
Did you allow the engine to fully warm up before testing? With newer engines that run leaner, you might have to let it warm up for 10 minutes or more before it'll run properly with the choke fully off.

Also have you checked for air leaks between the carb and the engine? Or possibly even a missing gasket?
.
It is always doing the same thing even after 1 hour of use.

Yes, all the gaskets and heat insulator are in good condition and are not missing
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post #6 of 38 Old 02-05-2018, 09:18 PM
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Quote:
Originally Posted by ELaw View Post
Did you allow the engine to fully warm up before testing? With newer engines that run leaner, you might have to let it warm up for 10 minutes or more before it'll run properly with the choke fully off.

Also have you checked for air leaks between the carb and the engine? Or possibly even a missing gasket?

Other than that, although the symptoms you describe 90% of the time are fuel problems, it's possible it's an ignition issue. Maybe see if you can find a used magneto (so you're not spending too much $ if it doesn't work) and toss it on there.
i have almost the same problem after i put on an aftermarket carb on my 1132. as long as i let it thoroughly warm up it runs fine. like 5-10 minutes. before then it will die or sputter when i try to move the throttle.

do these carbs run lean? is that the problem? how do you change that? would that be the pilot jet or the main jet?

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post #7 of 38 Old 02-05-2018, 09:19 PM
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Possible air leak somewhere? Sounds like a lean condition.

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post #8 of 38 Old 02-05-2018, 09:24 PM
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That's really weird. Swapping the carb should eliminate a bunch of potential (and maybe common) causes. But if you open the throttle plate manually and it still won't rev up, that (to me) sounds a bit tough to tie to an ignition problem. It's still running at the same RPM the whole time, so I'm trying to figure out how that could relate to the coil, as the sparks are still happening the same way.

An inline spark tester might be able to show you if you are losing spark. That's easy to try, and cheap, vs something like replacing a coil.

Is it possible the governor is connected wrong? Sorry to ask this, but when you move things manually, you're definitely only opening the throttle plate, and the choke plate is staying still, right? Just trying to think of easy things to check.

When it sputters, does it smoke?

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post #9 of 38 Old 02-05-2018, 09:41 PM Thread Starter
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I played with the main jet until I read rich spark plug condition with the same results.
There's no smoke when I try to open the carb butterfly with the governor rod
The choke isn't closed when I open the carb butterfly with the governor rod

Like you see, I tried everything,
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post #10 of 38 Old 02-05-2018, 09:46 PM
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Any chance you could post a video? Maybe showing the throttle linkage area, while you open the throttle manually, so people can hear what it sounds like?

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