OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Engines Questions On Honda Engines Honda GX120 no power under load

Hi all,

First post here by new member, am excited by all the amazing information on here, looking forward to learning and sharing...

I have a GX120 on a plate compactor, it starts first pull and idles nicely but has trouble under load, doesn't seem to develop full power.

With the engine uncoupled it seems to rev up quite well, and the spark plug is a good colour. I have been looking at the governor arm, because somebody else messed with it (true story) trying to fix this power problem, so I have been trying to get it back to basics, mostly then to figure out if there is a problem with the motor or maybe with the compactor vibrator unit itself.

I found the governor fiddly to set, and even now I don't have it right. Very minor tweak on the shaft/clamp will change behaviour from "won't idle" to "won't speed up". I got it to a point where it won't quite idle, but I can pull back on the arm by hand against the spring to make it idle, this is better than knowingly having it not reaching a good high speed. With the governor set like that I put the motor back onto the machine, but as soon as it is asked to load-up it lags and stalls, suggesting not enough fuel available, even if I push the governor arm to make sure the butterfly is full open.

So, without much load (just a clutch pulley) it will rev ok, but when asked to load-up it does not perform.

Would love to hear folks ideas on what this might be...

cheers, Brian

Brian_au,

Can you add some images of the area of the carburetor and governor. Also a picture of the air filter itself.

1. Did you try to run without air filter at all?

Have attached Owners manual that might help.

Hi Bruce,

Thanks for the manual, I will download and check it out. I have one photo handy of the gov, which I was going to post anyway asking if it is always so tricky to setup...
I have used the 'attachment manager' to upload the photo, is that the best way?
Following a youtube video I found, it said basically:

1. Loosen the arm clamp
2. Push the butterfly wide open
3. Turn gov shaft fully clockwise
4. Tighten clamp.

That got me close, but not quite right, I fiddled from there with very tiny rotation of the shaft from the initial set position, as I said still not perfect but close.

Good call on the air cleaner, I'll try that and report back, it certainly has that choking kind of sound under load like a blocked vacuum cleaner

First thing I would it try applying a little choke while under load. This will verify that if it is lean out problem as it will run better if it is. I would also do the basics like installing a known good plug as they do fail under load, adjust the valves, and clean the carburetor. I recently had a GX390 on a pressure washer where the plug gap was nearly .060", it couldn't even run under load without stalling out.

Might wonder why I suggest cleaning the carburetor. Here it is common for carburetors to clog up and just saves time to go ahead and do it.

Hello AVB, Brian and Bruce
Many thanks to all for the expert advice.

The answer is yes. But you can add text too (to the image).
You may add YouTube videos too, but this is done via the media tag button.

Cheers
Jack

Hello Brian, and welcome to the forum.
Reset the governor as per your initial instructions as this will start to play up when all else is running as it should,
I must concur with Bruce and AVB here, remove the filter, strip and clean the carby and and check your valve clearances cold, 0.15mm on the intake and 0.20mm on the exhaust.
Report back here once you're done and let us know how it all went.
Cheers, Ted

Report Part 1:
Tried running without air cleaner, same result. I checked that I could breathe through it when blocking the wing-nut hole, and reverse-blew it with compressed air anyway.

The extra replies and suggestions have turned up overnight as well, so thanks all for that info, I will look into those things and reply with a "report part 2" once I get through that. In the meantime I grabbed a couple more photos around the carb, have attached them here, let me know if any problems happen to be obvious to those with an experienced eye...You'll notice that the original throttle control arm has snapped off, a piece of wire has been substituted and works great, a cheap solution...

I had a Chonda engine on a go-cart in a while ago that wouldn't rev under load and produced black smoke like a diesel engine. When the wheels were lifted off the ground it revved happily without any sign of over fuelling. I checked the spark plug gap and tried it running it without the airfilter. Then I put on a spare carby to see if there was a blocked jet. I also removed the muffler as I have experienced them choking up with carbon but none of this made any difference. I decided to replace the spark plug even though it looked new just in case before I went any further. This turned out to be the problem! It can be so easy to overlook the plug even if it is brand new as they can fail under load but still produce spark. This turned out to be a valuable learning experience!

LRT,

I had the same problem years ago with repairs that we were doing on Victa two stroke engines when we had done points and condenser replacements. The client would return the machine under warranty and we ended up finding out that it was the brand new champion spark plug causing the issue. Hence we stopped using them and have never had an issue with spark plugs since.

Report part 2:
I got a new plug (ngk is my preferred), and a tin of carby cleaner, did the pull-apart of carby, checked and cleared jet holes, flushed passages with the cleaner. Didn't notice any issues to speak of, I'll post some pics later. The 'rubber' gasket between carb and air cleaner bracket has gone 'gooey', wonder if this is common or has somebody dissolved it with a harsh chemical? In any case, I don't think that is part of the problem.

Checked the cold valve clearances and found them to be perfect.

I reassembled, test ran, maybe slightly improved, I got the compactor to run one time nearly right, but next try was back to previous behaviour and motor stalled when asked to load up.

Given that I was now confident the motor should be in good order I turned my attention to the vibrator unit (also called an exciter). Bingo...problem located, bearings damaged and dragging. I didn't know what to expect in there, but it's a simple 'out of balance' shaft with open roller bearings at each end. Problem is that being open rollers they need oil, and there was zero oil in the housing...

I studied the sales brochure for the current model of this unit (Easymix 550H) which says 'sealed bearings, no oil required' so I will replace the open rollers with sealed bearings ASAP and will expect it to run up nicely after that.

Will post pics soon to enhance the thread for future lookers

Thanks Brian,
Amazing how sometimes the problem is nowhere near the where we originally start looking.
All should be in order after the bearings are replaced.

Yeah, I feel somewhat annoyed with the benefit of 20-20 hindsight, since I suspected the vibrator in the beginning, but the motor didn't sound right either under load, so I had to make a call on where to begin. I actually thought I'd go the easy path and swap the motor for another one, I had a Briggs on-hand with a clutch on it that I spent some time to get running, only to find that the mounting holes in the foot were not quite the same, so I couldn't even try it. By that time the Honda was unbolted and on the bench so I got stuck into that, finally coming around to following the first thought and getting the solution. Attached are some photos of the vibrator that I have marked-up with info labels.

All-in-all I don't regret spending a little time on the Honda motor, cause I have learnt some new stuff and found some great people on here with good advice offered promptly (thanks everyone who replied to the post). Hope to be poking around on here from time to time and maybe be able to return some help to someone else.

cheers, Brian

Yes it's rather embarrassing to find out that the spark plug was the problem! I also use NGK plugs as well. I have found they fail fairly early on worn out Honda GXV engines though.