Lawn Mower Won't Increase RPM's


Old 03-29-17, 06:26 PM
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Join Date: Mar 2017
Location: United States
Posts: 23
Lawn Mower Won't Increase RPM's

I have a Honda HRM21. This thing has been a great mower for my family and I for 20 years. Last year it sat for probably close to 6 months while I was working on fixing a couple things wrong with it.

Anyway, I got everything back together and it ran perfectly 5-6 times for a grand total of around 35-40 minutes. Point being, it definitely worked. Then, one time I go to start it and it will start on choke, but as soon as I kick up the RPM's it just dies out.

I've done all the easy things like fresh gas, new spark plug, new air filter. Additionally I've taken the carb completely apart and done a solid cleaning. All of the orifices on the carb were clean, but I went ahead and did a solid cleaning. Anyway, that was of no help, it does the same thing.

Is there a way to compression check the cylinder on these things? What are the chances my piston rings went bad?

A replacement carb is $45, so I could do that, but my gut just says that wasn't it based on how it clean it was.

Any recommendations? I'm a little afraid rust might have gotten to me while it sat.
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Old 03-29-17, 07:23 PM
Join Date: Mar 2017
Posts: 10
Sounds like it's starving for gas.
Gas filter???
Old 03-30-17, 01:44 AM
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Join Date: Sep 2016
Location: USA MI
Posts: 2,533
Check the governor / linkage!
Old 03-30-17, 02:16 AM
Join Date: Mar 2017
Posts: 10
Make sure all the springs on the carburetor/governor are still there and not broken.
Had the same problem with my chipper vac.
Would not increase rpm's.
I knew it was starving for gas.
Found an aftermarket carburetor for under $20.00 on ebay.
Gave it a shot and the engine is running fine now.
Sometimes even after a cleaning it's still not clean and it doesn't take much to mess them up.
Old 03-30-17, 04:46 AM
Join Date: Jan 2013
Location: U.S.A.
Posts: 1,472
On your list of easy things, make sure that the carburetor linkage actually moves when you adjust the throttle. If a clamp is loose or missing, operating the throttle can cause the casing to move without affecting the inner cable.
Old 04-02-17, 11:39 AM
Thread Starter
Join Date: Mar 2017
Location: United States
Posts: 23
I feel like such a noob. I forgot to subscribe to my own thread so I didn't get notifications that you all were helping! Oof!

It seems linkages are a common problem. But this will happen if I use my finger to increase the throttle (as in, I physically reach down there and do it). Are there still internal linkages on the carb that could be broken? But doesn't the fact that it does bog down tell me that the internal linkages are working? As in, the orifice plate is definitely opening and bringing in more air, but the gas isn't coming? It certainly sounds like definitively eliminating the carb is the number 1 step to troubleshooting!

Anybody got a known to be working spare Honda 16100-ZE5-005 carb sitting around?!?!

And silly question time, if I said I don't have a replaceable fuel filter, what would you all think? I'm inclined to think my filter is inclusive to my gas tank, but when I search for parts, I get nothing for my mower that let's me buy a replaceable fuel filter.

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