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Hi ,
I have a wheelie bin cleaning business and on one of the setups I’ve got a Honda GX 630. The issue is that it continues to run for about 3 seconds after I’ve turned the key to the off position. This has started since I changed one of the ignition coils, I have checked the gap and it’s set to 0.8 as recommended by Honda. Also fuel efficiency has dropped significantly, any advise please?
 

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Welcome aboard. What's a wheelie bin?

Don't know about the Honda's but my 23 HP Vanguards are wired to kill the spark for both cylinders at exactly the same time. If the Hondas are like that there should be a wire between the coils for that. I had one connection that was frayed and the wire was barely hanging on. It broke off when replacing a coil on the VG in my 420. If things got jostled around a bit replacing yours that might cause a shut down issue, like one coil grounding out first and then the other one after a delay. So you might be running on one cylinder when you shut it down until the 2nd coil is grounded. Or maybe the 2nd coil doesn't get grounded at all and the engine just quits at that point. It would likely sputter when it shuts down if that's what's happening. I don't see how a bad grounding wire would affect the gas mileage though. Is it running rough too?

This is what the VG coil wiring looks like.
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I'm assuming the engine is connected to a pressure washer pump with an unloader valve that lessens load on the engine when you are not spraying water?

Does that engine have a fuel shutoff solenoid in the fuel line or maybe an electric fuel pump? If the magnetos are not grounding out and shutting off spark, but the solenoid or fuel pump is shutting off fuel, the engine may run until the carb runs out of fuel.

As Army says, check the wiring going to the magnetos to make sure the magnetos ground out when the shut off switch is in the OFF position.

As for fuel consumption, is the unloader valve inoperative putting load on the engine at all times?
 

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Welcome aboard. What's a wheelie bin?

Could be the OP's site.

Who knew this could be an entire business segment? Based on the funk that emanates from my recycle bin seems like a heck of a good idea. 😎

Forgot my manners. Mark, welcome to the site. If you are in Brighton, you're not far from cousins of mine that live just the other side of Southampton in Swanage.
 

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Good point Mike. I didn't think of that. I also didn't explain what I was talking about very well. I should have mentioned there's a relay to kill the juice to both coils at the same time, on my VG's anyway. If the Honda twins have that feature and the wiring for it was inadvertently jostled a bit installing the new coil, it could be that only one coil is actually being grounded now. Then the engine quits because it doesn't like running on one cylinder.

The VG in my 420 is like that. I had a spark tester on a plug wire one day and the prod slipped out of the plug wire connector in the boot. The engine was idling at the time and it quit after a few seconds when that plug stopped firing and the RPM dropped. It chugged a bit shutting down too, similar to what happens when an engine idle is set too low. I have my gator wannabe set up like that. It's a Honda single cyl and I have the idle set so low the engine quits after only a few seconds if I get completely off the gas. It's intentional. The fwd/rev transaxle doesn't shift very well if the idle is too high. So what I do is get off the gas and flip the shift lever just before it quits then get right back on the gas. It's also handy if I'm getting on and off picking up branches or whatever. The switch to ground the coil is still in the ON position when I get back on the cart so I just have to hit the separate starter switch for the starter/generator and away I go.

I'm assuming the engine is connected to a pressure washer pump with an unloader valve that lessens load on the engine when you are not spraying water?

Does that engine have a fuel shutoff solenoid in the fuel line or maybe an electric fuel pump? If the magnetos are not grounding out and shutting off spark, but the solenoid or fuel pump is shutting off fuel, the engine may run until the carb runs out of fuel.

As Army says, check the wiring going to the magnetos to make sure the magnetos ground out when the shut off switch is in the OFF position.

As for fuel consumption, is the unloader valve inoperative putting load on the engine at all times?
 

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Yah they all have their own quirks and so do I ..so it gets pretty funky sometimes. :rolleyes::D

It’s so interesting how all our engines run different, we get to know them so well and learn the workarounds to get them to do what we want! 👍🏻👍🏻
 

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I repowered a little Case skid loader a number of years ago with a Honda twin (don't remember if 630 or 670) that used a fuel shutoff instead of a spark shutoff and associated lag to shutdown. The little 1816 was a good little worker with that engine but it went down the road after my construction project was completed. I remember it being an irritating "feature" to run the fuel down in the float bowl to save such a minuscule amount of fuel vapor in the world. Heck, I emit more gas than that.
 

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Some of the justification for a fuel shutoff and running the bowl level down is to avoid the thermal expansion of fuel into the intake manifold, causing flooding when attempting a re-start shortly after shutting down. For the 318 tractors, it is a good plan to lift the hood after just turning the engine off to allow the heat near the carburetor to dissapate rapidly, avoiding such flooding of the engine from fuel expansion... Most Onan engines in these 318 tractors will start up fairly well after about a half hour of setting, even if flooded from a bit of gas getting forced into the carburetor throat just after the fuel expands. Your experiences may vary of course...

Chuck
 

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One of my K532's isn't in use now but when it was I had a gas shutoff just before the carb because it would not quit using the key without dieseling. Sometimes pretty bad. I tried 2 known to be good fuel solenoids on it but no cigar. It was a bit annoying to shut it off that way but not nearly as aggravating as the chugging, pinging and death rattle noises. I actually shortened the hose as much as I could between the carb and shut off after this pic was taken. Took too long to quit otherwise. I had to remember to switch the key off after it quit but the 12V pump was good at notifying me the key was on. I inadvertently left it in the ON position one day and the pump clicked away for several hours before I caught it. Didn't cause any harm though. That was about 10 years ago and pump is still on that 400 and working fine.
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I have the wrong idle adjustment screw on my plow 400 and she idles just a tad high. I don’t like shutting it down at that speed so I pull the choke slightly to snuff her out and turn the key off. It’s probably a 5 min fix but I never have the time!🤣
 
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