Honda Lawn Engine Idle Surge

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ex_MGB

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Aug 30, 2002
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Salisbury, MD
I bought a Honda powered 17 HP Sears Craftsman lawn tractor two years ago. Last year it acquired an erratic idle where it would surge up and down at idle. This erratic idle occurs even after being fully warmed up.

I used to get an rough idle on my old Briggs & Stratton 18 HP lawn tractor when I put the manual choke off too soon. However, after running it a bit, it would go away. Not so on the Honda. It had a rough idle (where the rpm's go up then down, up then down) all last summer.

I ran some fuel treatment through the Honda thinking perhaps I had water in the gas line, but that didn't help. I also gave it a complete tune-up with fresh plugs, oil and filter.

Any ideas what causes this rough idle and how to get rid of it?
confused.gif
 
Drain the fuel bowl on your carb into a clean glass jar to see if there's any signs of debris.

See if you have a fuel filter and replace it.

Lastly, if all things fail, check and service/rebuid the carb and see how it goes.

Honda small engines are a breeze to service so long as you know all the fundamentals to it. (really!)
 
While I don't have a Honda powered lawn tractor, I do have a honda powered pressure washer and lawn mower. They both surge a big at idle and occasionally under a varying load. My honda engine's mechanical speed regulator/governor is too sensitive. I fixed the problem on both by increasing the rpm at which the engine operates (and idles) at so variations in load don't effect it as much.
 
Thanks. Air filter is clean. I'll have to really dig into it to find the carb fuel bowl. Not like the Koehler on my Troy Roto-tiller which is right there.

I'll see if I can figure out the engine mechanical speed regulator/governor setting and check the fuel filter.
 
ex_MGB,

Does the idle smooth out when a having the choke partially on? If it does, that means the reason for the rough idle is a lean condition.

Two things can cause a lean condition:

1) For a float carburetor, the float may me be set too low, not allowing enough fuel to enter through the inlet valve.

2) The throttle shaft could be worn, allowing air to enter around the throttle shaft upsetting the proper fuel to air ratio.

Before small engines were subject to smog regulations, you could compensate for a lean condition by turning a mixture screw, but now those mixture screws don't exist, leaving the carburetor to run on a pre-set fuel map that can't be adjusted.
 
The engine was only one season old when it started so I don't think it's a wear problem. I'll have to see if I can access the float although a guy at the office said it might be a "side draft" without a bowl?

I can't figure out why it all of a sudden started. Like I said, my old Briggs and Stratton would do the same thing if I killed the choke before complete warm up, but it would eventually go away. With the Honda, it doesn't go away.
 
I'm pretty sure all Honda's use float carburetors. You forgot to mention whether the idle smoothes out when partially choked; that's the key.
 
It's separate. I did some googling, apparently messing with the governor which if not working properly can cause idle surge, is not for the faint of heart.

I'm going to try and clean out the gas system.
 
I've seen two push mowers do exactly what you describe, except some black smoke when the idle goes down, due to excessively dirty air filters.

I know you say it's clean, but how clean is it?
 
Years ago I read that the surging is caused by jets or passages with goo/gum/gunk in them, usually caused by evaporated gasoline.

I had it happen to my old Troy-bilt tiller and cured it by cleaning out a passage with a tiny wire.

Nowdays, I add to my gas cans some fuel system cleaner and Sta-Bil before I fill them up. Haven't had that issue since the late 80's.
 
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Air filter is brand new as well as the foam pre-cleaner. One thing I'll say about Sears, when you call their 800 service number with just your name they can tell you the exact product you bought and ship you parts.

I ran fuel system cleaner through it, but it didn't help. I agree its probably a gas problem.

I had a horrible gas problem on my Troy-Bilt horse model with the 8 hp Kohler. Dang thing kept cutting out and wouldn't start. Took it to the place I bought it from twice. Problem persisted for two years. Finally I stripped it down yet again (I had the bowl off 20 times I'll bet, that and using starter fluid) and played with the pin that the float pushes in and out to shut off fuel. Sure enough, it was hanging up due to a sticky deposit. Cleaned it good with carb cleaner. Ever since then, I'm sure to shut off the fuel supply and run the engine dry at the end of the season. Goes to show its hard to get good service.
 
Personally, I use a variety. I figure one of 'em has to be doing something right.

I put it about 5-10 gallon's worth in a 5gal can, add some Sta-Bil, and fill it up. I do this every time.

I try to run my all the gas out of the machines each year but I haven't had any trouble with those I don't get to.
 
Quote:

Yes that does sound like a fuel issue then.

What fuel system cleaner did you use? Some of them are not as good at cleaning than others.

Click to expand...


I think Techron, it was last sumer. Any recommendations?
 
Is this your engine? A 17 hp Honda V-Twin?

GXV620.jpg


What I've found in the past is when a small engine isn't running right, I'll take the carb off and clean it out, after that; they seem to magically fix themselves. These little small engine carbs are not too terribly complicated; usually fastened to the cylinder with two 10mm screws. One screw usually holds the float bowel to the main body. You'll sometimes find sediment at the bottom of the bowel which comes out easy. I'll go ahead and check the float level before re-assembly. You sometimes have to replace the carb mounting gasket.
 
Techron seems to be a pretty good cleaner so I think you made a good choice with it.

Have you tried taking off the air filter and spraying carb cleaner in the intake while the engine is running?
 
Yup, that's my engine. I guess I could try spraying carb cleaner directly in the air intake but I'm not sure that would do the trick.

I guess I'll try and get at the carb. and bowl. I looked real hard and it didn't look easy to access.
 
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