The first item that has to be removed is the air filter box. It is held by three screws, two of which also hold the carburetor to the cylinder head. The third screw is to the right of the ones that hold the carburetor. So, take the cover off the air filter and remove the element. Remove the three screws. Pull off the fairly large black breather hose that attaches to the underside of the filter box. When you have done that, the carburetor will be accessible. It may be be hanging by its linkages unless the gasket stickiness is supporting it, so don't push down on it. Slide the clip that holds the fuel hose back, then remove the hose - you may have to rotate it on its fitting first, to free it up. I tend to push them off rather than pull them off, because when you pull them the hose stretches and contracts, which makes it tighter. I usually use a screwdriver at the free end of the hose, to push it back some distance, then pull it off the last bit of the way.
Unhook the anti-oscillation spring from the throttle butterfly. Hold the carburetor and push down on it steadily to separate the sticky gasket holding the insulator to the port, or the carburetor to the insulator. You don't care which one separates. Now you are ready to remove the two wire links (throttle butterfly valve, and choke) that are still attaching the carburetor to the engine. You need to rotate the carburetor gently so you can unhook each link in turn. Then you have the carburetor in your hand, and you can tip it upside down and unscrew the main jet. Put your hand under it, tip it back the right way up, and the jet should drop into your hand. The emulsifier is only held in by the jet, but it may not drop out. If it doesn't, look into the carburetor's throat through the choke butterfly. At the throat or venturi, on the bottom side of the carburetor you'll see a small round object sticking up slightly. That is the top of the emulsifier. Gently push it downward - a small Allen key is good for this. As soon as it moves and unsticks from the petrol gum holding it, the emulsifier will drop out through the hole you took the main jet out from. It is best to clean the jet and emulsifier by spraying carburetor cleaner through them. Note that the emulsifier has about 14 holes, including the top and bottom ones, and all have to be completely clean.
Now that you have the carburetor off, I'm going to refer you to three internet videos. One is an official Honda one that shows you how to do a perfect, elegant job of cleaning a GXV120 carburetor, which is not quite the same as yours. Don't worry about the video being in Dutch, he barely speaks anyway:
The other two videos show a heavy-handed galoot cleaning a carburetor identical to yours (but on a horizontal crankshaft GC engine, not a vertical crankshaft GCV engine - this slightly changes the process for removing and reinstalling the carburetor, so follow what I've said above rather than what he does). The galoot's carburetor also has exactly the fault that I think yours has: a blocked idle jet. He finds the problem at the end of the first video, then cleans it. He puts the carburetor back together in the second video. Here are the links to the videos:
You need to clean the whole carburetor, since you will have it off the engine and it has dirt in it. The first (genuine Honda) video shows the right way to do it. However the GX carburetor has a removable idle jet, but yours has a pressed-in, non-removable idle jet, so you have to clean it in situ. The galoot pokes a bit of copper wire through it. This is good if you do it correctly, and bad if you don't, since you could end up breaking off the wire in the tiny hole in the pressed-in idle jet, which would mean it was time for a new carburetor. The idle jet has a drilled hole in it which is only 0.35 mm diameter (0.014"), so the strand of copper wire would need to be quite small to fit through it. The tool the guy uses for the job in the official Honda video is a stainless steel cleaning rod, 0.30 mm in diameter. It is actually a device made for cleaning oxy welding torch tips, but the standard set of torch cleaners only goes down to 0.4mm: you need an extended set to get a 0.3mm cleaner. Up to now I've used a 0.3mm jet drill for the job because I only have a standard set of torch cleaners - I just got around to buying an extended set by mail order but they haven't arrived yet. Edit: When they arrived, the smallest was 0.4 mm, same as a standard set. I have not been able to source an extended set. However, I digress. If you are worried about breaking the copper wire off in the jet, just blast the jet from above with the carburetor cleaner and see if the liquid sprays out from the threaded hole the main jet screws into. If you squirt the cleaner down through the hole above the idle jet, after removing the screw-in plug from it as shown in the video, liquid cleaner should come out through the main jet mounting thread. If it doesn't come out from that thread, your idle jet is blocked and has stayed blocked. In most cases the carb cleaner will successfully blow out the crud without poking the copper wire through, but you will note from the first galoot video that he fails to dislodge the crud that way and has to use the copper wire.
Once you've done all the things the galoot does, hopefully in a gentler and tidier manner, it is time to put the carburetor back together, which he also shows you how to do (it is just a reversal of the disassembly process). You will need to clean the carburetor's and cylinder head's mounting surfaces for the insulator gaskets, and fit either one or two new gaskets. I think you will find your local Honda dealer will have two kinds of gasket available: one the same as the original equipment gasket, which is dark grey, and the official Honda aftermarket one, which is made from blue paper. If you use the grey one, it seals beautifully by sticking to the two parts it is squeezed between, then always splits when you dismantle the parts. The blue paper one does not stick and is therefore re-usable. Be very clear on whether you unstuck the gaskets on both sides of the carburetor insulator, or only on one side. If they are both unstuck, they have to both be replaced. Note that trying to reinstall a split gasket is almost certain to result in an intake leak and, at best, poor idle quality, but perhaps an engine that won't even start. (That engine should idle down to 1,500 rpm or less with car-like quality. If it won't, you have a problem.) If you follow the many internet reports of "carburetor trouble" with OHV Honda engines, from the symptoms most of them are actually split insulator gaskets. In many of the cases, the owner ultimately throws the whole mower away.
It is now time to reinstall the carburetor by reversing the removal process.
Edit note for archives: Readers should note that these instructions are for the GCV or GC engines. The GXV or GX engines are slightly different: the carburetor is mounted on two studs, rather than two removable screws, and there is a removable idle jet made from black plastic.
Last edited by Bruce; 12/08/1712:45 AM. Reason: Corrected Youtube
