Honda HRM 21-BB low compression

[lwalper]

I've struggled with this mower for the past couple of years - trouble starting, running badly. Have cleaned the carb a couple of times which (?)seemed to help. This season it just flat won't start.

I checked the spark, put in a new plug, sprayed a bit of starter fluid and it popped a couple of times. Thought "Well, maybe the coil is bad and not sparking consistently.

Pulled the plug and checked dry compression - 40 PSI - not enough to pop. Put a little 140W gear oil in the hole and and swirled it around a bit with the plug out. Recheck compression - WOW 175#. Squirted a little lighter penetrating oil in the hole and finally settled on about a wet 125 PSI. Reinstalled the plug, sprayed a little starter fluid and presto - runs great as long as I bleed in a little ether. Ran it for a couple of minutes on ether and rechecked the compression - about 100PSI warm. I'll recheck it again when it cools off.

Are there parts available for this engine - rings, valves etc to improve the compression? I like the mower and would like to get it running reliably.

 

[lwalper]

Good compression today, but carb leaks fuel from the float bowl. Need a new O ring.

 

[jp1961]

Hello,

There should be parts available, just check partstree.com with the engine model number.

Regards

Jeff

 

[bertsmobile1]

As you have already noticed taking compression readings on these engine is meaningless.
They have a mechanical decompressor built into the cam.
I will guess yours is on the way out & sticking or the valves are sticking.
Everything you need to rebuild the engine is available.

 

[EngineMan]

If the cylinder(s) are good put in a new set of rings and lap the valves at the same time, if the cylinder(s) are bad hone it out, it will be as good as gold after a good run in...!