Fast Idle unit on throttle bodies

RadioHowie · Aug 18, 2009

There was recently a discussion about Gen IIs suffering from poor fast idle issues and FredW and I came to the conclusion that the thermo-wax motor that controls the fast idle MIGHT be adjustable, at least from the graphic in the FSM.

Scanning eBay looking for a replacement cylinder head, I came across THIS set of throttle bodies for sale.

Fortunately, the seller took a decent set of pictures, including one where the thermo-wax motor is clearly visible. When the TBs are mounted on the bike, you can't see it for ****, but in the pics, it's plain as day.....

.....and good news for those of you suffering from "slow" fast idle, that sucker is obviously adjustable! The arrow clearly points to an adjusting screw, and it is directly beneath the throttle cable attachment points area, so should be visible from the top and accessible from the right with a long shafted screwdriver.

Could be a solution for those reporting "clunking" at cold start because the motor simply is idling too slowly.

Might be trial and error to get the idle where it runs comfortably, since as soon as you start the bike, the wax is gonna start melting and the fast idle will subside. But careful observance of the fast idle one day, a slight adjustment, then observing the next day, some of your clunking issues might go away, since it's simply an issue of the cold motor not having enough flywheel affect when first cranked.

johnny80s · Aug 18, 2009

Howie how is the fast idle different from the idle adjusting screw under the right side fairing?

RadioHowie · Aug 18, 2009

johnny80s said:
Howie how is the fast idle different from the idle adjusting screw under the right side fairing?

The idle adjustment screw you describe is the "normal" hot idle adjustment, which should be ~1100rpm.

The fast idle is the "automatic choke" of a fuel injected motor, that only works when the motor is cold. After the bike's thermostat opens, hot coolant runs to and from the two tubes seen at the end of the mechanism opposite of the adjustment screw I pointed to with the arrow.

So the bike warms up, coolant flows to the the fast idle device, melting the wax in the thermo-motor, the spring on the rail to the left of the device closes the fast idle ports and the idle drops down to normal.

As the bike cools down, the melted wax in the "motor" expands as it solidifies, sliding the rail back, opening up the fast idle ports for the next cold start.

Lots of posts I've read, especially involving Gen IIs "clunking" at cold start, the posters report idle speeds around 1400-1500 rpm. That's way too low for a cold motor when you consider a hot idle should be 1100.

Now granted, it's been 6 months since my FJR ran at all, but I'm sure I remember my fast idle being up around 2200-2500 rpm. Hey you Gen I guys...am I remembering correctly? Or is that 2200 to 2500 memory too high?

I'd be REAL curious to see a bunch of replies here from both Gen I and Gen II pilots as to what their fast idles actually are.

user 213 · Aug 18, 2009

Damn Howie, that's a long explanation just to say that the 'normal' idle adjustment is an air bypass adjustment that moves the idle up or down by allowing more air past the closed throttle plates.

Ya did great on the wax high idle adjustment description though. :thumbsup:

FWIW, my Gen I cold idle is just a tiny bit over 2k.

BwanaDik · Aug 18, 2009

This should be interesting. My fast idle is about 1500+ and yes, I do have the banging and clunking when first started cold.

A possible cure? Thanks Howie!

johnny80s · Aug 18, 2009

Thank howie. I actually got that. I just always thought the cold idle was 300 more than the fast idle.

My 07 idles as 11-1200 and the cold idle is around 1500.

Bustanut joker · Aug 18, 2009

Jus a titch over 2 grand fast idle here..But drops to 15 hundred about ten to fifteen seconds in.

:jester:

RadioHowie · Aug 18, 2009

Bustanut joker said:
Jus a titch over 2 grand fast idle here..But drops to 15 hundred about ten to fifteen seconds in.
:jester:

I think I remember mine taking a bit longer to start dropping....30-45 seconds or so, but I, like you, remember the cold idle over 2 grand.

Good stuff, guys....keep postin' up.

Too early to come up with a consensus, but it's interestting to note that 3 Gen Is, me, Bust and OCFJR report >2K fast idles and two Gen II reports, BwanaDik and FlockOfSeagulls80s report 1500.

I hope this thread grows with more quantitative info. I could start searching other threads, but a six-pack of

is calling my name. :drinks:

BkrK12 · Aug 18, 2009

My 2006 fast idle is 1500 RPM and there are no idle issues with it.

Interestingly, the service and owner's manuals make no mention of a high idle specification. The existance of a high idle device is only mentioned tangentially, by reference in one of the fuel system diagrams to plunger hose 1 and plunger hose 2. It causes a suspicion that Yamaha does no want people messing around with that device.

I'd stop by the dealer tomorrow and ask about it - if I thought I could find anyone there who could find their *** with both hands.

RadioHowie · Aug 18, 2009

BkrK12 said:
It causes a suspicion that Yamaha does no want people messing around with that device.

Of couirse they don't. It's part of the emissions system and that is strictly VERBOTEN!!! And that's why FJRs don't come stock with PCIIIs and Remus Hexacone exhaust systems.

user 213 · Aug 18, 2009

BkrK12 said:
I'd stop by the dealer tomorrow and ask about it - if I thought I could find anyone there who could find their *** with both hands.

Sometimes it helps to just ask for the 'Keeper of the Clue'. Some places will give you the blank look, others will immediately point you to the guy that has the Clue.

RadioHowie · Aug 18, 2009

OCfjr said:
BkrK12 said:

I'd stop by the dealer tomorrow and ask about it - if I thought I could find anyone there who could find their *** with both hands.

Click to expand...

Sometimes it helps to just ask for the 'Keeper of the Clue'. Some places will give you the blank look, others will immediately point you to the guy that has the Clue.

And then again, some folks couldn't get a clue if they were standing naked in a clue prison, soaked in clue pheromones and carrying a clue pardon. :rofl:

user 213 · Aug 18, 2009

RadioHowie said:
OCfjr said:

Sometimes it helps to just ask for the 'Keeper of the Clue'. Some places will give you the blank look, others will immediately point you to the guy that has the Clue.

Click to expand...

And then again, some folks couldn't get a clue if they were standing naked in a clue prison, soaked in clue pheromones and carrying a clue pardon. :rofl:

True. Sometimes I have offered them a dollar to purchase a clue, but that seldom works. In these cases, the only thing that truly works is to bring your Clue by Four. Looks like a baseball bat, but necks up to a 4"x4" square with "CLUE" burned into it on all four sides. Amazing how well it works!

user 213 · Aug 18, 2009

For RadioHowie and all the others out there that may need to deal with the Clueless. Save this to your downloads file and print some copies to keep with you.

buf2phx · Aug 18, 2009

At what ambient temps are you Gen I guys experiencing the 2k+ cold idle? My 08 barely idles faster cold than warm. Of course I am in Phoenix,and my bike has never been started below 75 degrees.

Guess I'll find out in a couple months what my cold idle speed is. I have not yet experienced any clunking,or any other adverse conditions, at idle.

Mike

Constant Mesh · Aug 18, 2009

Coolant flowing to the fast idle unit is not controlled by the thermostat.

user 213 · Aug 18, 2009

buf2phx said:
At what ambient temps are you Gen I guys experiencing the 2k+ cold idle?

It was 80F in the garage when I fired it up to check today. Ambient temp makes no difference in cold idle speed, just in the duration of the cold idle effects. On a really cold day with the bike left outside it takes a little longer to warm up to 2 bars, but still idles at 2k when I fire it up. At 100F, it still idles at 2k when the bike is cold, it just warms up faster to 2 bars.

On Gen Is, when the bike warms up to 1 bar, the idle drops some, then again when it goes to 2 bars.

RadioHowie · Aug 19, 2009

Constant Mesh said:
Coolant flowing to the fast idle unit is not controlled by the thermostat.

You are correct. One of the control plunger lines runs directly to the radiator, the other goes to the coolant pipe atop the valve cover, BELOW the thermostat, so there's pressure on both lines when the motor is running, whether the thermostat is open or closed. The thermostat only allows maximum coolant flow to the radiator when the coolant in the motor heats up the thermostat enough to open, allowing "bypass' to the radiator for further cooling, so the fast idle will get hot coolant long before the thermostat opens, making the unit actually more effective, since the "un-radiatored" coolant in the mtor will heat up a lot quicker than all the coolant in the entire system.

Good catch!!

Although I still think 1500rpm is too low for a "fast" idle on a motor with no flywheel. Hell, even my 15 year old Honda Del Sol fast idles at 2200rpm, and it's got plenty of flywheel to prevent "clunking", which I think is the motor stopping for a fraction of a second because a piston hits a "dead hole" that isn't firing because the motor's cold, so the cylinder basically becomes an air spring, forcing the motor to come to a momentary halt that makes the entire bike shudder and all the attached mechanical bits "clunk". The increased idle helps to overcome the relatively low inertia of the piston and crank assembly, essentially creating a virtual flywheel effect.

Basically, a motor spinning at 2500rpm is much harder to stop than one spinning at 1500rpm.

dsmack · Aug 19, 2009

RadioHowie said:
Basically, a motor spinning at 2500rpm is much harder to stop than one spinning at 1500rpm.

... unless, of course the valves contact the piston! :blink:

Nice explanation Howie. I think you are on to something here with the low cold idle and clunking.

Sorry for the above "***" NOT!

Don

Fast Idle unit on throttle bodies

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