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I had a similar question 10 years ago here, but this is a different GX31 engine, this one on a Honda "stick edger." Late last season, I could only run the edger maybe two or three minutes before it would start to stumble at throttle, and then die out. It would often restart immediately, then die out again. This season, it can only run about 30 seconds and it dies out.

I've also noticed it leaks oil from the end of the cylinder head. I don't know if it's from the plastic cover on it, or if I may have a bad cylinder head gasket, which could also explain the dying out when the engine starts to warm up.

From my "fiasco" 10 years ago (which I never fixed--I found a slightly used engine instead), I have an engine with low hours and a few parts I can scavenge. When I took the engine off of the stick edger, I noticed the fins on the cylinder block were dirty from oil. The coil also had some oil on it, and I know from past experience that engine oil on electrical components is not a good thing.

So I can swap over the coil, and, might as well do the spark plug.

I also wonder if the fuel filter is plugged. But, I don't know how to get at the filter--can I fish it out through the fuel filler, or does the rubber plug on top of the gas tank just pop out so I can access the hoses and filter that way?

All the fuel lines look good so far--it appears the black lines are the fuel lines, and the reddish-clear line seems to be a return to the carburetor from the tank.

Other than the stalling, the engine runs OK. There is no tapping or knocking from inside, unlike my other GX31 which had a tapping in the motor once it warmed up (as it was overheated from clogged fins on the cylinder).

Is there any reason to be concerned over the cylinder head gasket? I've never done one on a tiny Honda engine before, but I imagine it's not too difficult. And that plastic cover (cylinder head cover?) always seemed to leak slightly on all of my GX31 engines.

Final question--how do I get the clutch shoes off? Very thin 17mm hex bolts hold these on, apparently. I saw a trick using a small oil filter wrench to hold the clutch while turning the bolt. Or can I try an impact on it? I don't want to jam anything in the flywheel and risk breaking the fins. I also don't see any locating holes in the flywheel and engine where a dowel could be inserted to hold it tight.

Thanks!
 

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I'd have to crack open the service manual on that to be sure, but offhand I'd say the oil leak, which is a crankcase leak, is preventing the crankcase impulse to properly operate the fuel pump. I know it a 4-stroke, but I don't see those engines much and aren't sure how the fuel pump works offhand. Most 2-strokes must have that impulse function to work the pump in the carburetor. I can tell you that on a STIHL 4-mix motor if you have a CC leak, the fuel pump action suffers or quits altogether. I do know those engines aren't expensive, if you like the edger and use it a lot may be worth re-powering.

As for removing clutches. Stuffing pull-starter rope in combustion chamber acts as a piston stop, but if the you can get at the shoes I usually take 16" channel-locks and hold the clutch with them. ALWAYS be careful not to over-tighten clutch bolts, the head size is over-proportion to the shank size (usually 6mm), and will snap easily if using 3/8" drive. Use 1/4" drive and you should be ok.

Lastly, but since you have experience with these I'm probably preaching to the choir, those engines are easy to over-fill with oil, which could also effect the fuel pump impulse function.
 

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Discussion Starter #3
I swapped a bunch of parts over from the other GX31 and it seems to be running better now. Rather than do one part at a time and see which fixed it, I did them all at once. So I solved the problem but unfortunately did not find out exactly what it was.

It was later at night, but after letting it idle for several minutes and giving it throttle before shutting it off, it wasn't stumbling at all and didn't die out when it was hot. I'm giving it the full test shortly, under load.

This is what I swapped over:

Carburetor (had to transfer the new bulb over to the old carb)
Coil
Spark arrestor
Fuel filter
Spark plug (old one looked good, though)

The fuel lines were amazingly still intact after all these years. And aside from there being oil all over the engine, everything else looked good.

And for the clutch, I was able to get a screwdriver between the two mounting points for the bolts, underneath the clutch shoes, and it worked perfectly. The clutch springs were a little tired on the old one, and the blade on the edger would spin slightly even when idling. The blade doesn't turn at all now, when at idle, so that annoyance is fixed also.

But I still need to fix that oil leak. I'm pretty sure it's from the plastic part called the "cylinder head cover," as those are known to leak, and all of my GX31s have leaked there. If it's just a matter of it being a gasket, I'll order one in. I have some Hondabond here also if needed.

I have to grease the shaft from the engine to the blade--got the grease here, but need to get that done, and have to look up the procedure.

I think someone here once sent me a link to the service manual ten years ago, but that was a few computers ago and I don't know if I still have that anywhere. I really hate cannibalizing the old engine, but I still may see about getting it running again. The old GX31 overheated a little, so it may not even be repairable.

Thanks!
 

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Discussion Starter #5
I gave it a good workout Thursday--I hadn't edged properly since last summer (I could barely use it when the engine was dying out so often), and my parts swap had this GX31 running strong. I am going to order the head cover (in case it is deformed, like it was on the overheated engine) and gasket, and use some Hondabond to ensure it seals well. I did lower the idle speed, but I don't think I need to adjust anything else on the carb (if it's even adjustable).

I need to disassemble the gearbox and driveshaft for lubing--the gearbox is lubed through a removable hex bolt, but the shaft needs to be removed, cleaned and regreased with #2 grease (which involves the disassembly--unclamping the gearbox from the shaft). I discovered that the lever which locks the edging head in place broke off at some point (which is odd, since I hardly ever turn it), and had to temporarily clamp it down with a common nut, bolt and lockwasher.

Fingers crossed I get another 10 years out of it. :)
 
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