Honda push mower runs lean at idle

[Merkava_4]

Manufacturer: HONDA
Mower Model: HRN216VYAA
Mower Serial: MANA-2534311
Engine Sticker: GCV170 MY05 R260 GJAUA 2760371

Hi guys. I hope you all had a nice Christmas.

I'm working on this Honda mower that runs lean at idle as soon as the choke pulls off. When I say lean, I mean a mild fluctuation in RPM. While the choke is still on during a cold start, the engine runs perfect. Engine also runs fine with the blade engaged, but a little bit of a stumble going from fast idle to blade engagement. The problem is at fast idle with the choke off. The choke is the thermoxwax type. I've had the carb off for cleaning and stuck the straw into all the ports that the service manual says to spray. I don't think the carb was ever dirty to begin with, but I cleaned it anyway just in case something got into the idle circuit at the factory. The idle mixture needle is turned all the way to the left against the limiter stop. The carburetor has several main jets available for it, but the problem seems to be in the idle circuit.

[bgsengine]

Check float height? if it is a bit off (low when in normal operating position) fuel level may not be sufficient for idle mixing - Can be due to swelling in the float needle (if viton tipped type, or a viton seat) It was fairly common issue to have float height problems in the relatively older briggs pushmower float carbs (metal bodied ones) which almost invariably was caused by swelling in the float needle seats - new needle & seat kit usually solved that. Just one of the first things that came to mind that many don't really think about.

[Merkava_4]

Thanks bgsengine. I will try to find float level gauge 07401-0010000 that's listed in the service manual.

[KE4AVB]

And you may need to remove the pilot (idle mixture) screw. Instructions in the SM as to how to remove and of you will need a replacement screw set.

[hanz63]

To me it sounds like the typical low speed blockage they have. The newer HRN, I swear the passage is smaller than it used to be. When fully apart, use a straw on your carb spray blow through the hole below the screw to the stem. You have to be able to see it exit the stem when the passage is open. If you don't see the spray, it isn't open.

[SUKI]

To me it sounds like the typical low speed blockage they have. The newer HRN, I swear the passage is smaller than it used to be. When fully apart, use a straw on your carb spray blow through the hole below the screw to the stem. You have to be able to see it exit the stem when the passage is open. If you don't see the spray, it isn't open.

Tnx, for confirming my thinking on this. As something solid may lodge in the passage. Ultrasonic and other cleaner can only do so much. Sometimes it take actually getting in there to clear things. I once a had a grain of sand in a Nikki idle jet. If weren't a 10x loupe and a sharp eye I would had never found it. At least that don't happen every day.

[KE4AVB]

Thanks bgsengine. I will try to find float level gauge 07401-0010000 that's listed in the service manual.

Here is an aftermarket one if you don't insist on the OEM version.

https://www.ebay.com/itm/193106084027

Also you can use a caliper if you got one with the depth gauge feature. I use one when setting the float height on the Kohler Walbro carburetors when I replace the needle seats.

[Merkava_4]

I installed a brand new sealed in the bag Honda carburetor a few minutes ago. Engine runs exactly the same. This time I decided to take a microfiber shop towel and fold it into four layers. I held the four layers of cloth up against the air filter. At that moment in time, the engine starts to idle perfectly smooth without any dips in RPM. Take the layers of cloth away from the air filter and the engine will resume a pattern of RPM changes. The engineers wanted to make sure the engine doesn't run rich with a dirty air filter.

[bgsengine]

I installed a brand new sealed in the bag Honda carburetor a few minutes ago. Engine runs exactly the same. This time I decided to take a microfiber shop towel and fold it into four layers. I held the four layers of cloth up against the air filter. At that moment in time, the engine starts to idle perfectly smooth without any dips in RPM. Take the layers of cloth away from the air filter and the engine will resume a pattern of RPM changes. The engineers wanted to make sure the engine doesn't run rich with a dirty air filter.

Lesson #1: New is not the same thing as Good. I never trust a new part to work like it should out of the box. USUALLY they do, but SOMETIMES they don't.

Lesson #2: Your hunting symptoms even though alleviated by richening the mixture (choking) are not necessarily fuel related. lean surge can also be caused by a number of things including valve lash, air leaks after the carb (incorrect gaskets, incorrect gasket sequence, cracked insulators, cracked intake port, etc, etc.) and yes even spark plug and ignition problems can mimic a lean surge that goes away with richer mixture.

So, I'd not conclude that it was an engineering or new carb problem just yet...... All you have done is verifying that the issue is NOT caused by governor or governor adjustments, I'd say.

[KE4AVB]

Then the only option is jet resizing.

The standard main jet is a .68mm so you could try a .7mm (.0276) drill bit to enlarge it slightly. And the #70 (.0280) is the next size (.71mm) up.