OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Engines Questions On Honda Engines Honda GCV 160

Hi people, have a problem need help with. I have a Honda GCV 160 that is running erratically. It will start quiet easy ( usually by the third pull ) am able to take it off choke pretty much straight away but the problem is the revs are varying from high to low no matter what speed setting I have it on and once dropped below half throttle it will completely cut out. Have looked at other posts and tried a few things for example, resetting governor, cleaning carby & fuel system, spark plug, adjusting throttle cable but to no avail. No doubt it is something simple I am overlooking. Any suggestions would be appreciated.
Thanking you Paul.

Paul, is it cycling in speed continuously, with a cycle period of about 5 seconds? This is called hunting, and is usually due to lean mixture, but it can occasionally be due to binding in the governor linkage. On the other hand if the engine speed simply varies widely and erratically, it is not hunting and may be due to various causes.

Because your engine is a GCV, it has a toothed-belt driven overhead camshaft, not the pushrod system used on the commercial models. The Honda GCVs are rather prone to having that belt jump teeth on either the crankshaft or camshaft sprocket, resulting in a retarded valve timing and poor, erratic performance. If your problem is erratic running, with substantial loss of power, rather than hunting, please say so and we can talk about how you check the camshaft timing (which is very easy to do on that engine, fortunately, since you may have to do it from time to time).

Hi Grumpy, I am pretty sure it is what you call hunting ( counted and came up with approximately 5 seconds like you said, between the high to high revs).To fix the mixture is it the screw that the governor butterfly sits against or is that the idling screw. Could you also lay out some plans on the other causes you think it may be.
Thanking you Paul.

There is a previous thread covering a problem just about identical to yours, and I suggest you read it carefully:
https://www.outdoorking-forum.com.au/forum/u...p;Words=gcv160&Search=true#Post38602

Unless your governor linkage is sticking, which is a problem I don't recall ever encountering with a Honda, you have lean mixture. This would be caused either by an intake pipe air leak, or partly clogged jets in the carburetor. The idle jet would be completely plugged, and the main jet and/or emulsifier would be somewhat obstructed. This would have happened due to dirt getting into the fuel tank, and in due course piling up in the center of the float bowl and being drawn into the main jet, then migrating from there into the emulsifier and idle jet. The idle discharge port, which the idle mixture screw partly obstructs, may be blocked as well but more likely will not, due to the tiny size of Honda's idle jet. The idle jet is drilled to 0.35 mm diameter. The main jet on your engine will be about 0.55 mm or so (I haven't measured one on a GCV160, but it is 0.55 mm on the smaller GXV140) which is 2.5 times the area, so the idle jet is far more prone to blockage from fine particles.

I suggest you proceed exactly as very busy did in the thread I have referred you to. Don't leave out any steps: check the fuel feed system and the governor mechanism before you remove the carburetor. Check for possible leakage past the gaskets on both sides of the carburetor insulator. If at that point you haven't found the problem, clean the carburetor in detail as set out in that thread, in particular the on-line videos that are referred to. Report back as you go - we'll be happy to help at any point if you just ask.

I hope you'll keep us posted as you go.

Hi Grumpy, thanks for the info, will get stuck into it this arvo ( busy all morn ) will let you know how I go and if needing more help.
Thanking you Paul.

Hi Grumpy, I have rechecked from in-tank fuel filter through to carby, all clean with no leaks. Able to move governor arm with no resistance or pressure. Did read thread you suggested and watched the videos also suggested then went ahead and striped down carby and cleaned appropriately, slightly better but still jumping up and down in revs no matter the speed setting unless below half throttle were it will still cut out straight away. Do you think it could be the timing belt like you previously ( & like me ) hoping it wouldn't be.
Thanking you Paul.

Paul, I suggest you check the cam belt timing because it is easy to do. Even if the belt has jumped, retiming it is easy to do too. The only hard thing is if the belt has deteriorated, because you can't replace it without splitting the engine's crankcase, and that is a middle-sized hassle on the GCV engines because they have non-detachable cylinder heads, so the crankcases split diagonally to enable the pistons to be removed from underneath.

Remove the camshaft and rocker cover, set the crankshaft accurately on TDC on the compression stroke, and look at the timing marks on the plastic camshaft/sprocket as shown in this illustration from the public access service manual:



If the timing marks are both visible and level with each other when the crankshaft is in that position, the cam timing is correct. If they aren't level, say so and I'll explain how to fix it - a very simple operation. However if the belt shows signs of wear, life will get a bit harder.

Hi Grumpy, have just checked the timing and it is slightly out. The timing mark on left hand side of the picture you have sent me is above the other one in a clockwise direction, about the width of two timing marks together. Would this be enough to put the timing out. Have had a good look at the belt and it is in good condition, no signs of fraying or wear and tear.

Paul, any timing error must be an exact number of belt-tooth-pitches. The least the belt can jump by, is the distance from (say) the right side of one tooth, to the right side of the next tooth, so the belt pitch is approximately twice the width of a tooth. I suggest you measure that distance on either the belt or the camshaft sprocket, then compare it with how far out you think the timing mark is. If it coincides, I'll post details of how to re-time it. However the re-timing just consists of moving the sprocket in the forward direction by one tooth relative to the belt. It does not verify that you've corrected an actual timing error until you put it back together and repeat the timing check. If you retime it only to find that it was a measurement error and you've moved it from right to wrong, you'll probably be irritated. Remember, at this point you've said that you cleared the carburetor jets, including the tiny idle jet that you can't even see properly, let alone touch, because it is down inside the carburetor. That cleaning job can't be done with petrol and then looking or prodding at the jet, it absolutely requires an actual pressure can of carb cleaner and verifying that the cleaner squirts out from the central threaded hole the main jet screws into, when you remove the threaded plug above the idle jet and squirt carb cleaner down into the hole underneath it. If you dismantle the camshaft because you didn't clean the idle jet properly, you will not end up regarding this as having been a good day.

Please post a picture of the sprocket, belt, cam and rockers taken from "above" (that is, at right angles to the axis of the crankshaft, so the rockers and camshaft are seen in plan view) so I can explain the next bit.

Hi Grumpy, did some accurate measuring and the belt had actually moved two teeth ( is it normal for the belt to be able to move so far or has my local mechanic not taken enough notice when putting it back together ). I marked the sprocket and belt with a white pen were they should end up after rotating sprocket ( in the right direction). Turned motor over by hand checking every compression stroke only, for a number of turns, all lined up perfectly. Put back together, decided once more to check carby ( nice and clean ), guess what, purred like a kitten at any speed, no cutting out under half throttle and no hunting. Please let me know if there is something I should do or haven't done or to keep an eye on for the next couple of mowing's.
Thanking you Paul.

Well done Paul, I wasn't sure you'd have room to pull the shaft all the way out to free the sprocket/cam so you could retime it. If you have to remove the engine from the base machine you add at least half an hour to the time the job takes.

The GCV engines are notorious for jumping their timing, and for breaking the plastic sprocket/cam. Neither is difficult to fix but I prefer reliable engines. (The GCVs also have no oil seal on the governor shaft, and it is not unusual for them to leak oil there).

I have read a couple of reports that it is common for the timing to jump once on GCVs, when the engine is relatively young, then not do it again until they get old and the belt is worn out. I can't imagine why your local mechanic would have had occasion to pull that shaft out, and if he didn't take it out, I doubt he'd have put it back in with incorrect cam timing. It seems more likely yours is just one of the ones that happened to jump. If it happened repeatedly you'd eventually have to replace the belt and/or sprockets, but as you've seen, it is not a big job to retime it. I've also read that there is a service fix consisting of a revised sprocket and belt, to reduce the likelihood of jumping:
http://www.hobbytalk.com/bbs1/archive/index.php/t-255329.html

If you have any pictures, please post them.

In response to your actual question, I suggest you should pay attention for a while to whether the engine loses power suddenly, after it has been shut down. Timing nearly always jumps during the engine's stopping or starting mode, when it passes through relatively low speeds of rotation.

I've had the experience of driving a car that had jumped its timing chain, and it was not difficult to tell that it had happened: it was way down on power, and very sluggish in its throttle response (highly evident when changing gears). It was a pity that my father was sitting in the back seat insisting that nothing was wrong, which resulted in us having to drive it from Perth to Kalgoorlie flat out at 35 mph, by which time it needed a new cylinder head and a new set of valves. However, I digress yet again. With items like lawnmowers, they are often used at much less than full power and the changes I've described might not be so obvious, especially if it just jumps one tooth rather than two. Nevertheless it is because it may only jump one tooth, that I think power loss and very sluggish running is more likely to be the main symptom if this happens again, rather than inability to run at less than maximum speed.

Thankyou Grumpy and Paul foot , this has bee an excellent thread for me as I have one of these mowers from bunnings and as it turns out after about three mows it to had similar issues. Mine would never idle after I washed the blades through the base hose outlet and went to turn it down to an idle . It sounded as if it missfired anthen cut out,ever since this happened it never ran quite right and so after following this thread it had me thinking so I had to have a look . It just so happened the belt was out by a tooth. Now the honda runs like brand new and only took ten minutes cheers and thankyou .

Thanks for posting that roebuck, it sounds as if your timing jumped when that engine did a convulsion whilst stopping, which is a classic way to get that result. The ancient car I mentioned in this thread jumped its timing while shutting down also. It "ran on" in Australian terminology, or "dieseled" as the Americans say: hot deposits in a combustion chamber caused it to fire a few shots with no particular ignition timing, after the ignition was turned off. Combined with a worn timing chain, that was all it took. In some ways a toothed rubber belt acts like a worn-out chain, because it can stretch a bit and deform its belt-teeth quite a lot, when it runs erratically. Once a momentary slack develops, it can easily jump a tooth, especially on the small crankshaft sprocket.

I'll close this thread.