My Toro Lawnmower with GCV160 Honda engine had its 5 years warranty expiring 10 days ago. It starts at the first pull, but just today it decided to rev up and down with a period of about 1 sec, so I do not know if this qualify as "hunting" which has been described as having a period of 5 seconds. Here is a youtube video I uploaded showing the sound it makes:
Sometimes after 25 seconds or so the issue disappears, only to return after having used the mower for 5 or so minutes, but most of the time it does not go away after 25 seconds and it just keeps doing it, unless I start fiddling with the governor arm and I make it increase the motor speed while holding the governor steady, once I don't feel the governor trying to move I let it go and the motor stays stable for few minutes.
This mower has not been used more than perhaps 120hrs in 5 years, I prepare it following Toro recommendations and store it indoors during the winter (Nov-April). The governor arm to carburetor linkage looks fine to me, I swapped the spark plug between my Snow-blower and the lawnmower (they are the same type) and the issue didn't move to the snow blower and the mower still behaves the same with the snow blower's spark plug. I have adjusted the ignition coil to flywheel gap to 0.016", it was 0.010" or so.
Should I follow the recommendations for "hunting"? Or is this something different?
That is an unusually short cycle time for hunting, but I think it likely that is nevertheless what it is. Please clarify one point, though. Does the cycling cease if you apply the choke slightly? If so, the problem is likely to be lean mixture. In that case if the carburetor has not been disturbed recently - in particular by loosening the attaching studs - the most likely problem is dirt or gum in the carburetor. A dirty fuel filter is also a possibililty, but a somewhat less likely one, because as I understand what you have said and demonstrated, it cycles immediately after it has been started, whereas an upstream fuel flow restriction would only cause lean mixture after a delay while the float level in the carburetor dropped below its normal level. On the other hand, if the carburetor mounting has been disturbed, leaking insulator gaskets would be a strong possibility.
If you cannot stop the cycling by applying just the right amount of choke, it is unlikely to be lean mixture and we will have to go back to first principles. The solutions in that case will probably be found in the governor mechanism inside the crankcase - but that is relatively unlikely at this stage.
You said: If the carburetor has not been disturbed recently - in particular by loosening the attaching studs - the most likely problem is dirt or gum in the carburetor
The carburetor had not been disturbed ever, until couple of hours ago. You were right above, the issue was in the carburetor, I noticed the smaller of the holes in the Main Nozzle were restricted by gum (I assume), I did general cleaning of the carburetor based on youtube videos and not only the hunting issue was resolved but since last summer I noticed the so called Toro Personal Pace self propel system lacked power, likely the carburetor jets were clogged since then, that minor inconvenience was also solved after the the carburetor cleaning. Many thanks for your prompt and accurate advice.
Thank you for reporting back so promptly and accurately, Barro. I'm glad the problem was one that is somewhat usual and fairly easily fixed. From what I have seen that engine is capable of giving good and reliable service, as well as being particularly easy to start and operate, while being unusually smooth-running and pleasing.
There are a couple of characteristic weaknesses, in particular a risk of the camshaft drive belt jumping a tooth or two, or if you neglect to keep the cylinder head cooling fins free of dirt or grass, overheating and subsequent valve gear problems. However even if these things occur they are usually very easily fixed. Please let us know if at any time the engine ceases to run well - we'll be glad to help.
