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Mower RPM - Governor or Carburator?

#1

N

NJDan

When I start my Honda mower it revs like crazy to about 6000 rpm (3100 recommended max setting). I don't let it do that for very long. Prior to this I had to take my engine apart to fix a connecting rod problem but I never made any adjustments to the governor. I also did not take the carb apart and try to clean it. It seems to me there is a governor problem somehow but before I tear the engine apart again I wanted to rule out anything else. Is it possible that the carb could be causing the high revs and not the governor? I don't believe there is an idle adjustment on this carb. It's an HRX217K4HZA. Any suggestions?


#2

sgkent

sgkent

the speed of these small engines is normally regulated by a governor. Some use a vane that moves in the breeze from the flywheel and some use a gear assembly. Maybe some late FI ones use electronics. I'd be looking at how you hooked the governor back up.

maybe #7 is the assembly in the engine. Then there are some rods that relay to the carb. At lease this is the pictorial that comes up online for that mower. https://www.hondapartsnation.com/oemparts/a/hpe/505ce4a5f870022d24bdc70e/oil-pan


#3

B

bertsmobile1

First guess is when you replaced the sump you have not captured the governor or while apart the bob weights got out of place


#4

N

NJDan

sgkent said:
the speed of these small engines is normally regulated by a governor. Some use a vane that moves in the breeze from the flywheel and some use a gear assembly. Maybe some late FI ones use electronics. I'd be looking at how you hooked the governor back up.

maybe #7 is the assembly in the engine. Then there are some rods that relay to the carb. At lease this is the pictorial that comes up online for that mower. https://www.hondapartsnation.com/oemparts/a/hpe/505ce4a5f870022d24bdc70e/oil-pan
Click to expand...
Yes, that is the correct drawing. There is a gear that meshes with the gear on the crankshaft. This spins two weights that raise and lower the pin that pushes on the governor "paddle" that is connected to the governor arm outside of the engine.


#5

N

NJDan

bertsmobile1 said:
First guess is when you replaced the sump you have not captured the governor or while apart the bob weights got out of place
Click to expand...
That's what i'm trying to confirm by process of elimination. I was worried about the governor because you can't see it to confirm that the gears mesh, but then you can't get the cover back on unless they do. I can't specifically recall where the paddle arm or pin was when I put everything back together. If the carb cannot be the cause of this and the linkage between the governor arm and the carb is normal then it has to be the governor, right?


#6

N

NJDan

NJDan said:
Yes, that is the correct drawing. There is a gear that meshes with the gear on the crankshaft. This spins two weights that raise and lower the pin that pushes on the governor "paddle" that is connected to the governor arm outside of the engine.
Click to expand...
Another comment on that drawing. Item 12 the governor arm shaft actually has to be turned up 90 degrees so that the flat end rests against item 11, the governor slider, right? I can't be 100% sure that I checked this but I can't imagine that I didn't. I might be able to confirm this because there looks like there is a groove on the end of the shaft that you can grab with pliers and turn if needed. I don't think I see that groove on mine, which means it might be facing down making it hard to see. I need to look at that when I get home. That might be the confirmation that I need.


#7

B

bertsmobile1

When you refit the governor you must make sure that the shaft , part # 12 is touching the slider , part 11 and the slider itself is engaged with the bob weights
They can be a little tricky .
To confirm the governor is not working start the engine then manually work the governor arm
As you speed up the engine you should feel the governor pulling against your finger and the faster the engine runs he harder the governor should push.
It is easy for the shaft to end up in the wrong place , 180 deg out so it is not touching the slider
Bad news is that usually causes the slider to fall off so it is back into the engine again .


#8

N

NJDan

bertsmobile1 said:
When you refit the governor you must make sure that the shaft , part # 12 is touching the slider , part 11 and the slider itself is engaged with the bob weights
They can be a little tricky .
To confirm the governor is not working start the engine then manually work the governor arm
As you speed up the engine you should feel the governor pulling against your finger and the faster the engine runs he harder the governor should push.
It is easy for the shaft to end up in the wrong place , 180 deg out so it is not touching the slider
Bad news is that usually causes the slider to fall off so it is back into the engine again .
Click to expand...
So I just looked at that part 12 and there is no groove on it to get a pliers on. It is just a round pin so I can't confirm that it is in wrong. However, your comment about resistance is helpful. When I have the mower on full throttle and the speed spring is tight the governor arm is vertical and in its most clockwise position. When I throttle down and release tension from the speed spring the governor arm is supposed to turn counterclockwise and slow the engine. In my case this doesn't happen. I actually made a video on this but nobody replied. If I take what you are saying correctly then the governor should be providing the force needed to move the governor arm when throttle is reduced (when it is running, of course). The spring on the linkage to between the governor arm and the carb is probably there only to keep the linkage from being loose and has nothing to do with pulling the governor arm. Here is the video:



#9

L

lefty2cox

Correct. That spring just takes slop out of the linkage from what I understand. I agree with Bert. She's coming apart again. Don't feel bad. It's a right of passage. I know I've been there. Look on the bright side...you already know how to do it so it should go a lot quicker this time.


#10

N

NJDan

lefty2cox said:
Correct. That spring just takes slop out of the linkage from what I understand. I agree with Bert. She's coming apart again. Don't feel bad. It's a right of passage. I know I've been there. Look on the bright side...you already know how to do it so it should go a lot quicker this time.
Click to expand...
LOL. Thanks for the encouragement. I don't mind redoing it. What I mind is if I redo it and then somebody says, "Oh, that's not the governor. It's just xyz problem with the carb. But, yes, I can tear this thing down in no time at all now! I'm going to take a photo of what I find in there. I better not find a perfectly functioning governor! The more I understand the more it looks pretty clear.


#11

B

bertsmobile1

I will hazard a guess here that the actual governor mechanism has failed
What usually happens is the engine then over revs and the con rod snaps just below the little end from over reving.
So the broken con rod was not the cause, it was the symptom .
To understand the way things work consider it to be a tug-O-war between the governor spring and the governor.
When you open the throttle the spring stretches
When at rest the governor is fully open so the throttle opens fully
as the speed increases the governor pulls ( pushes if you like ) against the spring
The governed speed happens when the tension on the spring is balanced by the governor working against it
So the governor is always trying to make the engine go slower but the force it does this with is dependent upon the speed the engine is rotating at.
zero rotation = zero governing force
High rotation = strong governing force .

In practice a governed engine should run forever so when something internal breaks you always have to find out why it broke before you replace it .
Mower engines are made very cheaply so the con rods are not particularly strong
Most will let go at around 5000 rpm because the engine is designed to never exceed 3600 rpm ( 3200 for most Hondas )
A rookie mistake when using a mower engine in a go cart or mini bike was to remove the governor and use a direct throttle control and a broken rod is the usual result .
"it was running great, then it just went bang & stopped " is something I hear regularly from the racing mower mob


#12

sgkent

sgkent

bertsmobile1 said:
I will hazard a guess here that the actual governor mechanism has failed
What usually happens is the engine then over revs and the con rod snaps just below the little end from over reving.
So the broken con rod was not the cause, it was the symptom .
To understand the way things work consider it to be a tug-O-war between the governor spring and the governor.
When you open the throttle the spring stretches
When at rest the governor is fully open so the throttle opens fully
as the speed increases the governor pulls ( pushes if you like ) against the spring
The governed speed happens when the tension on the spring is balanced by the governor working against it
So the governor is always trying to make the engine go slower but the force it does this with is dependent upon the speed the engine is rotating at.
zero rotation = zero governing force
High rotation = strong governing force .

In practice a governed engine should run forever so when something internal breaks you always have to find out why it broke before you replace it .
Mower engines are made very cheaply so the con rods are not particularly strong
Most will let go at around 5000 rpm because the engine is designed to never exceed 3600 rpm ( 3200 for most Hondas )
A rookie mistake when using a mower engine in a go cart or mini bike was to remove the governor and use a direct throttle control and a broken rod is the usual result .
"it was running great, then it just went bang & stopped " is something I hear regularly from the racing mower mob
Click to expand...
makes sense. Fix the symptom and not the root cause is a common issue in repairing and restoring things.


#13

N

NJDan

bertsmobile1 said:
I will hazard a guess here that the actual governor mechanism has failed
What usually happens is the engine then over revs and the con rod snaps just below the little end from over reving.
So the broken con rod was not the cause, it was the symptom .
Click to expand...
Well, in my case the snapped rod was caused by lack of oil. :mad:
bertsmobile1 said:
To understand the way things work consider it to be a tug-O-war between the governor spring and the governor.
When you open the throttle the spring stretches
When at rest the governor is fully open so the throttle opens fully
as the speed increases the governor pulls ( pushes if you like ) against the spring
The governed speed happens when the tension on the spring is balanced by the governor working against it
So the governor is always trying to make the engine go slower but the force it does this with is dependent upon the speed the engine is rotating at.
zero rotation = zero governing force
High rotation = strong governing force .
Click to expand...
Thanks. Part 11 pushes against part 12 to govern the speed. If the throttle is lowered part 12 will be in a slightly different place since it is connected to the governor arm but that probably doesn't matter. It's a little hard to visualize what effect that small change makes. The net is that wherever the throttle is, the governor will maintain that speed.


#14

B

bertsmobile1

All done with levers
The actual governor slider would be lucky to move 1/4" which becomes near 3 " by the time it gets to the end of the governor arm outside the engine.


#15

N

NJDan

I got the engine apart to see what's going on with the governor and here is what I found. One of the weights was sticking and so it appears that the governor was not able to provide the force needed to push the arm. I did two short videos. The thing is that I saw this before I closed it up. The weight was stuck and I unstuck it thinking it was OK. That's the price of inexperience. I don't know if it is me or Honda but in disassembling the mower I snapped one of the engine mounting bolts. The first time I took everything apart both exhaust muffler bolts snapped off and I had to get a friend to tap new threads.

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#16

N

NJDan

Just to close out this thread -- I put a new governor in the engine and got it running again. The mower ran at the perfect RPM right off the bat! Lesson learned. If the governor weights are not moving freely all the time when you touch them then replace it! I do have another issue now but that's a different thread.


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