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J.R., Small Engine Technician
Category: Small Engine
Satisfied Customers: 7445
Experience:  Owner of outdoor power equipment business, repairing all makes and models.
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honda gx420 clone engine dies out

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I have an electric start Honda clone GX 420 small engine. I just put on a brand new carburetor, new spark plug (not sure of the gap) and new air filter. I do not have a fuel filter in the line. The only thing I can adjust on the new carburetor is the idle screw. I set that so my engine idles at perfectly. My engine starts and idles fine for about 40 seconds, then abruptly dies. After that, I can start it and it will run for only about 25 seconds. any thoughts? I do not have the original gas tank on my engine, I have it sitting about a foot and a half away with a 3/8 fuel line. Would that matter? I put took the flywheel off and added a new magneto. I obviously had to take the ignition coil off and I put it back on. Could I of done something to the ignition coil??
The first thing that I would do is make sure that the gas tank is setting higher than the carb. I would then run it until it quits and as soons as it quits have a pair of vise grips ready and crimp the line going to the carb. Once you have the line crimped crack the bowl nut off of the bottom of the carb and see how much fuel it has in it. It should still have a full bowl if the fuel is getting to the carb correctly. If not fuel comes out, then you probably have something like a bad line or something in the tank. If you still have a good amount of fuel in the carb take the bowl off and make sure the jets are clear in it. It may have a piece of machining debris or dirt in it.
Customer: replied 7 years ago.
The gas tank sits about 8 inches higher than the carb. I just ran the motor until it quit, then I clamped off the fuel line. I cracked the nut off the bottom of the bowl, and fuel poured out. I took the bowl off, and it had no debris floating in it. Keep in mind this is a brand new carb. When I first got this motor 2 weeks ago and tried it out, the symptoms were the same, so I got a new carb. I even hooked up a brand new gas tank off a honda gx200, and the motor did the same thing. Could I have a bad motor? Is this a sign of weak compression or something? thanks for your help!

I think maybe you did get a bad engine. Maybe the valve seat is loose in the head. Did you remove the nozzle from the center of the carb and check the holes in the sidewall.

Customer: replied 7 years ago.
Hi JR-It was so weird, the engine would run perfectly and then shut off like somebody turned a key. I thought maybe something might be acting up with my low oil shut off switch. I disconnected it, and sure enough the motor now runs like a top. One question though, my motor (same as a Honda gx390 or a Honda gx 420) has two oil dipsticks. The dipstick towards the back of the motor (carb side) reads as the machine is full of oil. The dipstick at the front of the machine (near starter and low oil shut off) reads no oil. The engine is mounted at a very very slight slant (you have to really look hard at it to notice it is not perfectly level), so it would not surprise me when comparing the oil dipsticks together were off a bit, but to have one read full and one read empty? They don't have separate chambers do they? Will it hurt the engine if one dipstick reads way above the fill line (if I add more oil) and the other reads way below the fill line?? I have no idea how much is in the machine right now..and I just changed the oil this past weekend. I didn't pay attention to how much oil I put in, rather I just read the dipstick towards the back of the motor near the carb. When it read full, I stopped putting oil in the machine.
If the engine is on a tiller, then disconnect the low oil switch completely. I have done several repowers and all brands that I have used ( Honda, Briggs, Etc.) acted up and would quit running due to the bouncing. If it is not on a tiller, then use the dipstick that is closest to the oil switch.
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