Hand throttle idle problem with NHC-250. RPM's rise after a minute or two.

[1 Patriot-of-many]

My 923 NHC-250 idles fine except when I use the hand throttle. I'll set it say at 900RPM, it will stay at 900 RPM for a minute or two and then start increasing rpm on it's own till it's screaming. Any idea what is causing this and the solution?

 

[Truckoholic]

That's very interesting. Sounds like the vibrations are causing the linkage to tighten further and increasing the engine speed. Can you tell if the handle actually moves further out on its own, or does the handle itself stay in the same spot?

 

[jasonjc]

I've got 2 M818's and they do the same thing. Don't know what to tell you.

 

[M215]

If I start our M813 while cold and set the hand throttle to a higher RPM to warm up the engine it will do the same thing. Never had the need to use the hand throttle after the engine is warm to see if the same occurs.

 

[1 Patriot-of-many]

That's very interesting. Sounds like the vibrations are causing the linkage to tighten further and increasing the engine speed. Can you tell if the handle actually moves further out on its own, or does the handle itself stay in the same spot?

Handle does not move at all. Notice the rpm's with my foot throttle are a little unpredictable too. Hold it steady and the rpm's don't stay steady.

 

[73m819]

Till the ip heats up, you WILL get the rpm rise, let the ip heat up to operating temp, then use the worthless hand throttle, I did away with the oe hand throttle and replaced it with a veneer cable, once thing are warmed up, I have rpm adjustment down to a few rpms at a time.

 

[1 Patriot-of-many]

I will see if it that's the case, thanks.

 

[162tcat]

It's a pt pump thing. They do that. Pt is "pressure timed" so as the rpm increases, even a little, the pressure increases then rpms increase and the cycle repeats. This continues until it hits the governor.

 

[painter paul]

I have found some of the 939 series better than the older 800 series. The older ones are almost impossible to use.

 

[Tornadogt]

Both Nc250's I have A0 and A1 939Series trucks do the same rpm gain with hand throttle when warming up.. . Seems to be nature of the beast.

 

[jatonka]

It is the nature of the beast. Plain and simple. There was no reason to ever put a handle throttle in any 855 Cummins dash board. If you need a throttle to set RPMs for a pump, then you need to buy a constant speed governor from Cummins or other engine supplier. All of the log loader trucks around here with Cummins power have these constant speed governors installed. JT

 

[Coffey1]

My 84 923 did the same thing.
My 90 BMY works like a charm I can set it and walk away it hums right where I put it.
M923A2

 

[73m819]

After reading some more comments, I will say again, let the IP warm up to OPERATING TEMP BEFORE you use the hand throttle, this WILL do away with the rpm surge.

 

[jw4x4]

My 932A1 does the same thing. I only use it when its really cold. The whole idea of using the hand throttle is to idle the truck at 900-1000 rpm until it reaches operating temp. I know to be standing close by, when it starts climbing the revs, I climb up and push the lever in.

 

[Suprman]

Seems like it would create an issue on a winch truck or wrecker when in pto operation.

 

[162tcat]

It's totally normal with a pt pump. They have a high idle governor available for applications that require it.

 

[1 Patriot-of-many]

Both Nc250's I have A0 and A1 939Series trucks do the same rpm gain with hand throttle when warming up.. . Seems to be nature of the beast.

You said a bad word.......

 

[Coffey1]

Lol the dreaded A0. Everyone needs Tared and feather for ever saying A0.
Or keel hauled for saying A0.
Firing squad for using A0.

 

[Coffey1]

Did I say you should not use A0 lol.

 

[jw4x4]

Seems like it would create an issue on a winch truck or wrecker when in pto operation.

NEVER winch without a competent operator behind the wheel. A crane truck (wrecker) is different.