High Idle Cap Loose on Yanmar 3YM30

[EmeraldCoastSailor]

I recently noticed that my high idle cap isn't tight on my 11 year old engine with 1000 hours. I am not sure it ever was. Does anyone know if it needs be tight? It isn't coming off; just loose and able to spin.

On a related note, I have noticed my idle RPMs seems to be low and I am looking to adjust up a bit. This is how I discovered the loose high idle cap.

[jimbunyard]

'Free to rotate' doesn't seem to be the normal condition for an adjustment bolt, and though the service manual (in my quick perusal) doesn't say to tighten it, there appears to be a lock nut on both idle adjustments, which would seem to indicate they should be locked...

Manual here, https://j109.org/docs/yanmar_3ym-2ym-service-manual.pdf adjustment procedures seem simple enough.

[jimbunyard]

Looked at it again, there is a cap on something called the 'FO limiter'. Don't know what 'FO' signifies (fuel output?), but if that is what you're referring to, it should probably be snug.

[tkeithlu]

" it should probably be snug."

Jim, you can go beyond "probably." There's no point to an adjustor bolt, or any other bolt on an engine, being loose. Given that Emerald is concerned for idle speed, and this is an idle speed adjustor, the obvious route is to adjust it and see what happens to idle speed. It should bear against the throttle in some manner. Since you have the drawing, can you advise Emerald on what it does?

[jimbunyard]

Really too much to be conveyed here, which is why I linked to the manual. In case ECS's out of internet scope, here's a couple pages from the manual.

[EmeraldCoastSailor]

I am learning about this subject via the parts manual and your input (which I appreciate); my initial thought was that the high idle element was distinctly different than the low-idle adjustment bolt. My problem seems to be that I am getting too much vibration at too low of an idle (less than 700 RPM).

PDF of the governor parts attached.

[jimbunyard]

Originally Posted by EmeraldCoastSailor

I am learning about this subject via the parts manual and your input (which I appreciate); my initial thought was that the high idle element was distinctly different than the low-idle adjustment bolt. My problem seems to be that I am getting too much vibration at too low of an idle (less than 700 RPM).

PDF of the governor parts attached.

It's not unusual for different manuals to have conflicting or wrong information, or to even have it in the same manual.

In your parts breakdown, it is unclear if item 139, the hi speed cap, is threaded or not. If not, it may or may not be free to spin, it doesn't matter if it does; the nut 11 should be tight and should hold the hi-speed limit screw in place.

If item 139 is threaded, hold nut 11 with a wrench (after ensuring that it is locking the high idle screw in place) and just snug 139 up to it to hold it in place.

To adjust the low idle, loosen nut 87 and adjust idle with screw 78. When you get it where you want it (book says 825), lock it there with nut 87.

Before you begin, make sure the throttle cable is securely fastened and has full range of motion in both directions.

[Wotname]

Originally Posted by jimbunyard

Looked at it again, there is a cap on something called the 'FO limiter'. Don't know what 'FO' signifies (fuel output?), but if that is what you're referring to, it should probably be snug.

FO = Fuel oil i.e. diesel
(AFAIK)

[skipperpete]

Originally Posted by EmeraldCoastSailor

I recently noticed that my high idle cap isn't tight on my 11 year old engine with 1000 hours. I am not sure it ever was. Does anyone know if it needs be tight? It isn't coming off; just loose and able to spin.



On a related note, I have noticed my idle RPMs seems to be low and I am looking to adjust up a bit. This is how I discovered the loose high idle cap.

Any chance it’s the anti tamper cover as in this case, also on a Yanmar

[EmeraldCoastSailor]

Skipperpete,
That is exactly what it is. WDYT?

[tkeithlu]

If you are getting strong vibrations at a particular RPM, or narrow range of RPMs, you are likely dealing with a resonant frequency, a frequency of produced minor vibration that drives greater vibration, in the same way as a tuning fork vibrates at one frequency when struck. All physical objects have resonate frequencies. In the general case, do not set your idle in that range, or run the engine at that speed when underway.