idle / idling down issue

[Pat Conlon]

Wait a second... lean pilots should be worse with a cold motor and should improve as the motor heats up.  

To quote from the Factory Pro Mikuni CV carb tuning recommendations:
"....If the throttle is lightly "blipped" at idle, and the rpm "hangs up" before dropping to the set idle speed, and there are no intake leaks and the idle speed is set at less than 1000 rpm, the mixture screws are probably too lean: try 1/2 turn out, to richen mixture. Be sure there are no intake leaks and the idle speed is set at less than 1000 rpm!...."
http://www.factorypro.com/tech/carbtune,CV,high_rpm_engines.html

Bob, assuming #2 thru #4 is correct (in my above post) set your idle speed to 1,000 rpm, then as the engine heats up, do the "blip test" if your engine does not return to idle (continues to race) turn your idle jets out by 1/2 turn.

Note: The center adjusting knob below your carbs (accessible from underneath) sets the idle speed, and the 4 idle jets are located on the top of the carb.
The throttle plates on the carbs are synchronized by the 3 adjusting screws located on the shaft of the throttle plates. If you tried to set the idle speed by messing with any on these 3 screws *stop* you will need to re-synchronize your carbs before you go any further.

Hope this helps.

[andyb]

To quote from the Factory Pro Mikuni CV carb tuning recommendations:
"....If the throttle is lightly "blipped" at idle, and the rpm "hangs up" before dropping to the set idle speed, and there are no intake leaks and the idle speed is set at less than 1000 rpm, the mixture screws are probably too lean: try 1/2 turn out, to richen mixture. Be sure there are no intake leaks and the idle speed is set at less than 1000 rpm!...."
http://www.factorypro.com/tech/carbtune,CV,high_rpm_engines.html

Yes Pat.  And the line right above the line you quoted:
"...NOTE: A lean problem gets better as the engine heats up."

 A blip test is not the same as the idle running high as it warms up.  

I've seen this happen in two ways, the first was when you came to a stop in town, the idle would run 2500ish.  Loading the bike against the clutch with the brakes on would bring it down to 1100 (where it was set), and it would stay there until the next time you came to a stop.  The cure was a synch, that time.

The other way I've seen it happen was a partially plugged set of pilots with old gas nasties.  The idle was actually set at 3000rpm, but the bike took nearly 20 minutes to get all the way to temp on a cooler day!  So it would idle fine after a few minutes worth of riding, but after an hour's ride, it wouldn't come down at all.  Cleaning the carbs' idle circuits made the difference (and then turning the idle way, way down!)

In both cases iirc the carbs had come off before finding the cure, so it's possible that there was a mild air leak that got worse as things got warm that was fixed by reseating things during assembly.  

Because this is a bit of an unknown machine, I'd personally just tear it apart, write down whatever's in the carbs currently, give everything a good cleaning followed by a synch, and start from a known set of condiitons.  You could try running seafoam or the like through it and twiddling the mix screws (which would very likely help if it was purchased from a significantly different elevation or something), but if you're going to have plans for things like new filters, pipes, and so on, knowing what's in there and knowing it's right will save a bit of waiting later on when moditis kicks in

[mr blackstock]

I had the same problem with my FJ1100,

it occured to me that perhaps the idle was adjusted to high, and letting mixture through as well as the idle circuit, so I have dropped the idle screw down, riched up the idle jet so the bike only runs from the idle circuit, just in case the carbs are a little out in sync.

Well the results are great, the bike idles well, no more surging, no more dipping of the idle.  It will suffice until I can get a decent synch, which as soon as I sort out the electrical problem, will be soon I hope.

good luck, give it a try...

cheers, Gareth

[Toy4Bob]

thanks all for the replies, looks to be some great info here.  To be honest, I am not much of a mechanic, but my son is, so I am trying to gather info for the next time he comes home LOL.  I guess not sure he is up to a carb sync, and I think that takes special equipment(?), so may have to think about a dealer visit.

When I got the bike it basically came right out of winter storage, and the owner said he didn't ride it a whole lot last year.  He seemed to be knowledgeable mechanically wise, but who knows... heck, for all I know he is among the members of this board.

In the mean time the way I make sure it isn't idling at 2500 at every stop, I find that if I don't engage the clutch and brake, not engage the clutch until almost stopped, it will idle down and rarely pop up, although now and again it will.

[Toy4Bob]

Oh, and thanks for the surfing tips... I completely missed the most recent post, inread, replies, etc buttons, they blended in I guess 

[Pat Conlon]

Yes Pat.  And the line right above the line you quoted:
"...NOTE: A lean problem gets better as the engine heats up."

I never said that it didn't....So Andy, I gotta ask you,  which way would you go with the idle jets?  Leaner or Richer?

Don't sidestep my question and suggest a full carb overhaul... Just a simple answer please, leaner or richer for a hanging idle?

Sheesh

[racerman_27410]

the investment in a method of synching the carbs cannot be understated with this engine.

the morgan carbtune is very nice and if you have the means i highly recommend it. There are also some designs for build yer own but either way i would consider this to be an essential tool to own.


I personally sync my carbs whenever i feel the vibrations start to pick up in the engine. its not unusual for me to have to re-sync the carbs at least once a season if im riding her hard.......  Its very noticeable on the early model FJs (non rubber mounted engines).... just being out of adjustment a small amount makes a big difference in the amount of felt vibes.

and if you can pull the tank off you can sync the carbs... its super easy.



KOokaloo!

[racerrad8]

thanks all for the replies, looks to be some great info here.  To be honest, I am not much of a mechanic, but my son is, so I am trying to gather info for the next time he comes home LOL.  I guess not sure he is up to a carb sync, and I think that takes special equipment(?), so may have to think about a dealer visit.

It will probably be cheaper if you buy your own sync tool and do it yourself. There are plenty of horror stories of guys taking their FJ in to a dealer only to receive terrible service because the kids working on the bike weren't even born when it was made and they look at it as an old piece of junk.

I sell a lot of these, Sync-Pro

You can find all of the information on what you need to do in the Carb Files section.

Randy - RPM

[SkyFive]

Yes, buy tour own sync tool. It will save you money in the long run as you will probably use it two or seven times.

[andyb]

Yes Pat.  And the line right above the line you quoted:
"...NOTE: A lean problem gets better as the engine heats up."

I never said that it didn't....So Andy, I gotta ask you,  which way would you go with the idle jets?  Leaner or Richer?

Don't sidestep my question and suggest a full carb overhaul... Just a simple answer please, leaner or richer for a hanging idle?

Sheesh

Pat, with what he's describing, I'd try a synch.  And yes, I'd then take stuff apart and see what's in there.  A hanging idle that can be forced down and stays there until the throttle is hit again doesn't mean the idle mixture is wrong, it says something else is.  Or possibly the idle mix is comically, hilariously wrong, but you'd think there'd be other symptoms at that point.  I do agree that richening them a quarter turn or so would be a way to test what's wrong, as it should help if the pilots are undersized, adjusted lean, or marginally plugged, but that should also show up in other ways, for example surging at slow cruise and excessive warmup times.

I make a point of trying to assess the problem before doing much of anything, you know that

[RichBaker]

Just got an 89 FJ1200. 

Then about 10 minutes later I thought I heard an electrical whine, but realized it was the gas tank slowly releasing pressure... is this normal, or could there be a vent plugged?  I kinda wondered if that was the case, could it be causing the uneven erratic idle?  BTW, the tank was only about 1/2 full.

My '90 has been doing that since I got her with 2300 miles on her, in 1994.... don't worry about it, I've never heard of a fuel-pump bike thaat needed a flap-ectomy! I've heard brand-new Yamahas sitting on the showroom floor do it....

[flips]

Hi all.

Not being an fj carb guru but reading through this thread a thought struck me.Is it possible that maybe one of the slides may be sticking?.Is it worth checking that the slides all snap back down?A weak slide spring perhaps?.Just a thought

Cheers

Jeff P

[andyb]

Jeff, my #4 carb did just that for awhile... after a long blast through the gears staying at WOT, it'd stick in the fully up position.  Made it blubberingly rich until 6k or so, and normal after that.  If it happens, you'll know it;   gives you a rough idle, as fat as a harley through the midrange, and with an FJ top end!

A light touch with engine oil to the slide cured it.  Never found anything it was hanging up on either, I assume it just was getting cocked a bit at the top and getting stuck.

[flips]

Hi Andy.

I was wondering what the symptoms would show if a slide stuck just short of fully down.I guesstimate that it might be like badly sync'd carbs,although with the butterfly closed maybe just too rich?.I had one do it after rebuilding my carbs but noticed it before reinstalling them.Pulled out the slide,gave the slide and carb slide bore a clean,little spray of wd and reassembled and everything was good.

Cheers and thanks for the info!

Jeff P

[racerrad8]

Hi all.

Not being an fj carb guru but reading through this thread a thought struck me.Is it possible that maybe one of the slides may be sticking?.Is it worth checking that the slides all snap back down?A weak slide spring perhaps?.Just a thought

Cheers

Jeff P

The slide not fully seating should not have effect on the idle. The throttle plates at the closed and idle position will not allow enough vacuum to draw fuel from the emulsion tube.

If the engine is idling you can reach in and manually raise the slide with your finger, You will get a slight increase due to the fuel on the needle as you raise it, but is should subside right back to idle.

If the slide is raised, then as soon as there is enough vacuum to draw the fuel it is really rich as the needle is in a raised position and allows to much fuel to pass. It will be really rich until the needle range is reached and then it will run fine.

The basics of the carbs have to be in good working order and the adjustments have to be within the range to get the thing to run right. If there are vacuum leaks, frayed/sticking throttle cables, etc then it really doesn't matter what the carb is doing those things have to be addressed first.

Hopefully, the issues will come to light when the son arrives.

Randy - RPM