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I can't find any info on the exact carb on my HRX217K4HZA. Photo below. I rebuilt the engine and my idle is a bit high. I identified the auto choke thermowax as one problem (thank you, Honda forum!) and confirmed today that the new one is working. I'm looking next to whether this carb is adjustable. There is a screw with a spring on it but this screw seems to go through the body of the carburetor. It's hard to imagine it's function but I know some of these carbs have an idle screw.

What do you think?

do you have a tachometer to check the idle speed? Don't do it by ear. Just a little circular one will do. I think they also have some smart phone apps that listen to the frequency and tell you what the RPM is.

The screw in your pic is the idle adjusting screw. Reducing the engine speed can be done by ear, but increasing speed it’s best to use a tach.

Yes, I have a tach, which why is I know it is running fast. Never heard of the tach app. Sounds interesting.

I'll give the idle screw a try. I was hoping that is what it was. The other adjustment is to bend the governor arm, but even with no tension in the spring and the throttle on low it still idles well over the recommended 3100 rpm so hopefully the idle screw will do it. Does that screw turn a baffle or something inside the carb? The screw goes right through the housing.

The screw should be touching a small arm the throttle plate when the engine is running. You should not be able to to slow the engine down, by pushing the plate tighter against the screw, if the governor is working properly.

First make sure you do the static governor then set you idle speed.

Rivets said:

The screw should be touching a small arm the throttle plate when the engine is running. You should not be able to to slow the engine down, by pushing the plate tighter against the screw, if the governor is working properly.

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I'm not sure I understand. You mean it won't work if I adjust the screw while it is running?

StarTech said:

First make sure you do the static governor then set you idle speed.
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By "static governor" do you mean to adjusting the governor screw and making sure the arm and governor pin are fully clockwise?

I mean while the engine is running can you slow the speed down by pushing on the governor arm? If you can, backing the idle adjusting screw out will make now difference in idle speed. If the engine speed doesn’t change, then backing out the screw should lower the idle speed.

Rivets said:

I mean while the engine is running can you slow the speed down by pushing on the governor arm? If you can, backing the idle adjusting screw out will make now difference in idle speed. If the engine speed doesn’t change, then backing out the screw should lower the idle speed.

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I see what you are saying. I'll have to try that when I get home. The question is whether I can set the mower to idle speed and then lower the speed more by pushing on the governor arm. I think I can but let me try.

So I doublechecked the position of the governor arm and the pin to make sure the governor was putting up enough fight. I loosened the nut and make sure it was adjusted right. It actually fired up with a little too low RPM! That was the issue. I bent the governor arm a little and that put the run speed right in range. It does idle a little slow now but finally I can adjust the idle screw to fix that. Run speed is perfect.

Thanks for the help, all!