Fast Idle Return

[Tikvah]

(Part #9 in the picture)

I'm working on installing my air throttle and I needed to remove an air cylinder I didn't recognize. 
On the governor the Fast Idle is a cylinder mounted into the side of the governor box.  On top of the governor is the throttle control lever, the engine stop cylinder, and the Fast Idle Return cylinder.
The air lines runs through the Fast Idle Return to the Fast Idle cylinder.

So, maybe a dumb question....but:  why do we have a Fast Idle Return?  Won't the throttle springs return the throttle to the idle position as soon as the Fast Idle is turned off?

Lastly, if anyone has done an air throttle on this engine, how did you re-install the Fast Idle Return?

[luvrbus]

I don't understand the question,the line comes from skinner valve has a tee at the back of the holding cylinder then to fast idle cylinder basically 1 line with a tee at the holding cylinder that is the only way I ever saw one installed  

You don't want to remove number 9 without doing away with the air supply to fast idle cylinder that engine will go into orbit when the switch is flipped ,it (9) holds the governor to prevent over speeding it's not a return cylinder confused yet

[Tikvah]

Yup, confused.  The book calls it "Fast Idle Return".  Maybe the name confuses me.  Obviously it is needed or it wouldn't be there, but it just seems that when the fast idle releases the throttle springs would return it to idle, just like when you take your foot off the pedal.

[luvrbus]

I have no idea why MCI calls it a fast idle return and they will return to idle once the fast idle cylinder air supply is off but without the cylinder holding the governor there is no control of the speed

The fast idle cylinder pushes on the buffer inside the governor if you notice the 2 work in sequence together cannot be any other way

[bevans6]

I call it the fast idle throttle lock air cylinder, since I never bothered to find out it's real name.  It pops out and locks the governor speed control lever in idle.  With the added spring of the fast idle and the idle spring together, who knows what would happen if you then added speed control spring to that?  It might turn inside out...

As said, they both activate together from the same air feed, and don't even think of installing a fast idle without the throttle lock.  It would be too easy to step on the throttle when fast idle was activated, you need the lock.  On my MCI there is a spring loaded mechanism that connects the throttle cable to the speed control lever, it is designed to save the cable if the throttle pedal is stepped on when fast idle is on, it's a spring in the cable connection.

Brian

[luvrbus]

I went to the book(DD bible) to make sure I haven't been calling it by the wrong name all these years it is called a "air controlled throttle lock" section 14.3.4

[Tikvah]

Thanks guys, I think it's starting to make sense.  Somehow, when the Fast Idle is switched on the governor has no idea how far to go.  That seems like a goofy way to build something.  They could have just put a cylinder on the throttle that gives it a little fuel instead of one that releases total chaos and another to hold it back....must have been some engineers on the loose that week.

Anyway, my Fast Idle hasn't worked in awhile, so I'm not too worried about it.  I need to figure out some way to mount the cylinder back on top of the governor.  I might wait till I get back south someplace to deal with that.

P.S.  The air throttle is really cool.  I haven't done a test drive yet to test the transmission modulator, but the pedal is much lighter.

[luvrbus]

Your 6V92 should have a fuel modulator if not be prepared for lots of the middle finger salutes till you get the hang of it they will roll the black smoke

[Tikvah]

Your 6V92 should have a fuel modulator if not be prepared for lots of the middle finger salutes till you get the hang of it they will roll the black smoke

Okay, more information please.  I have no idea what you're talking about.  My bus never smokes -ever.  Other than some whit smoke on cold start.  But never any black.

[luvrbus]

You have fuel modulator(delay) under the valve cover to keep the rack from opening wide open till the speed builds up it is controlled by oil pressure that's why no black smoke remove it they will blow smoke.

It controls the engine on take off makes no difference if the pedal is on the floor  some people like the setup then some remove it and deal with the smoke for faster acceleration  

[Tikvah]

Hmmm, that's interesting.  There is so much I dint know.  I'm just glad when I turn the key it starts every time and I'm on the road.

[Dave5Cs]

So you mean there is a way to go faster than the guys walking down the road, Interesting!.....

[RJ]

So you mean there is a way to go faster than the guys walking down the road?  Interesting!.....

Except for your 5C, Dave. . . 

[bevans6]

On my engine the fuel modulator/delay was on the number two cylinder of the driver's side bank, but it controlled the entire injector rack system.  It's just an oil filled dashpot, like a shock absorber.  It slows the movement of the rack from idle to higher than idle.  You can adjust how much resistance it has by drilling out the oil hole.  I think on an engine with an automatic transmission you wouldn't notice it was there, but I removed mine, it made blipping the throttle for down-shifts noticeably slow and was a pain.  You only see them on turbo engines because the smoke issue is due to the turbo lag.

The idle system of the MUI engine is based on a separate spring.  It is set with pre-load to set the idle speed of the engine.  The buffer spring is a very light additional spring that stabilizes the idle spring system and allows for a smoother idle.  If you have a Jake switch on the buffer that switch detects when the buffer spring has engaged with the idle arm, that is how it knows the rack is in no-fuel - the idle system has engaged.  The fast idle system is an light additional spring that only can be engaged with the engine at idle.  It adds the strength of the fast idle spring to the pre-loaded setting of the idle spring to get the higher speed.  If you play with the strength or pre-load of the fast idle spring you can adjust the fast idle speed, but I have never tried to do that so I don't know how to do it.

Brian

[luvrbus]

You notice they are there on a automatic also Brian I had those things laying around for years now people are going back to them,you can never figure out the bus group me I don't really care for one the delay or the modulator