Idle Speed, Won't drop below 2.5 unless forced.

[David Allaband]

Hi all. This is my next emergency.

My 1993 FJ1200 with 40K miles on it has an idle problem I don't understand. I recently balanced the carbs. The bike runs better now, less stalling and hesitation and jerky throttle response. Unfortunately the Idle now doesn't drop below 2.5K rpms unless I force it down. By that I mean if I hold the break and let out the clutch to slow the engine, it will slow down and then idle happily at 1.3K rpms. However, as soon as I get it up over 2.5K rpms again it will use that as it's new idle speed until I force it back down again. It's a problem for city ridding.

There are unlimited problems, I know. I have had these carbs apart three times in the last couple months, I cleaned and reoiled the K&N air filter. I'm going through this beast over and over again trying to get the engine to run smooth and it's very unrewarding. I'm surprised that such a new bike with so few miles and a gentle life for at least 20K of it's 40K miles, has this many problems. I've pulled much older bikes off of scrap heaps and had them running better then this bike in just a few hours.

Any ideas on this problem would be greatly appreciated!

[weymouth399]

Possibly the exhaust leak you may have, if you havn't installed new exhaut gaskets. Or at least tightend all other pipes up. If that's all good you may need to adj the fuel screws a little.

Bob W

[fj1289]

Couple ideas to try:
1. Make sure you don't have an intake leak.  Could be a cracked carb tubber, a cracked or missing vacuum cap, the vacuum line to the tap not connected, or carbs not seated well in the rubbers. 
2. Check your idle mixture screws.  Make sure all are at the same setting from a LIGHTLY seated position.  If that checks, try richening the idle mixture slightly and see if it improves.

Couple other ideas - make sure the throttle cables are lubed, free and not binding.  Also check to make sure the slides aren't hanging up (had one once where the needle was rubbing on the emulsion tube and caused enough friction to keep the slide from dropping all the way without some extra help. 

Let  us know what you find!

Chris

[markmartin]

I had the same problem after syncing mine this summer.  I was finally able to get it to idle at 1000 - 1100 after much frigging around with the idle screw--bring it way down, then creeping back up very slowly. Tightening up the clamps at the carb boots seemed to help.  I was tentative about trying to get it to 1200rpm in fear of getting that surging idle again, similar to what you describe.  I did not try the fuel screws--that was going to be my next move.

Let us know when you find what works for you. I'm planning on a carb rebuild this winter --maybe new carbs--??  I'm interested in what you find out.

Bob, good suggestion, I'll torque my header bolts,  maybe get new gaskets while I'm at it.

[Sideburns]

This kind of throttle response also occurs when one of the slides doesn't close properly.

When one of the slides doesn't close properly, you sync it with the carb next to it by the fact that you close the throttlevalve more than the other.
So they seem the same. until you open the throttle and the one with the faulty slide is already open further than the other one.

So the one with properly working slide has a throttlevalve that is open further.
When you then open and then close the throttle, the properly working slide has a throttle valve that is open far enough to keep that one going.

Can anyone translate this into understandable English? I'm not a very good at explaining.   

[David Allaband]

Thanks everyone! Lots of advice on this one!

I'll check for vacuum leaks but I've been looking for them for a while now so I don't think I'll find any. I think I'll check my idle mixture screws next. I'm fairly certain they are not right (I moved them around a bit but nothing happened so I just tried to get them back where I found them).

Just to make sure.

The idle is supposed to be around 1,200rpm?
The idle mixture screws are supposed to be screwed all the way in and lightly seated? Or you screw them out from there? I've done this on other bikes and I could feel, hear and see the difference when I turned the idle screws. I turned these ones and nothing really changed.

Thanks again for all the ideas! Your comments will be my checklist for trouble shooting!

Dave.

[Pat Conlon]

David, when you re-install the carbs, do you feel a 'click' when you push the carbs back on the intake boots?  You should.
A vacuum leak or hanging slide would be my bet.... You want to get it fixed asap. A vacuum leak, sucking air will lean out the fuel/air mixture and cause that cylinder to run hot.

Report back if you don't mind and update us on what you find.   Cheers!  l 

[andyb]

When mine did exactly as you describe, I found the synch to be off.  A few minutes to check will clear your mind, if nothing else.

The idle spec is 1050, give or take 50, I think.  1200 is fine.

Mixture screws are turned in (clockwise) until they seat lightly, then backed out as many turns as you desire.  Usually 1.5 to 4 is the number there, if it needs more than that, your pilots are too small, and v/v.

Are the carbs fully cleaned?  If you're not seeing changes from the screws, I'd wonder if the passageway that feeds them is partially plugged.  I always felt like they were a bit insensitive also when compared to other bikes, but it definitely should be something you can feel when you're riding it gently.

Are your float needles and needle seat orings working properly?  Ditto the orings in the choke plungers?  It could be that you're feeding a vastly screwy mix due to a leak in one of those places, and it'd show up at idle more than anywhere else.

Sideburns describes a slide sticking in the up position (or partially up).  When I've had that happen, the engine was terribly rich and blubbery at low speeds, though it'd clear up and sound better the harder you wound it up, running crisply and well past 7k or so.

Easy to tell if you're lean or rich (too much fuel or too much air, in either case a leak someplace) is to ride it up to temp, then let it idle a few and read the plugs.  If you read the plugs after just warming it in the garage, they should be quite black.... odds are the choke's on when you start it cold like that, right

[RichBaker]

The idle is supposed to be around 1,200rpm?
The idle mixture screws are supposed to be screwed all the way in and lightly seated? Or you screw them out from there? I've done this on other bikes and I could feel, hear and see the difference when I turned the idle screws. I turned these ones and nothing really changed.

Thanks again for all the ideas! Your comments will be my checklist for trouble shooting!

Dave.

If nothing is happening when you adjust the idle (pilot) screws, that means the idle circuit is still dirty/plugged.....If the pilot jets are stock, you want the screws about 3 - 3.5 turns out from lightly seated.  You need to pull the pilot screws out and make sure the o-rings and washers are there, then spray carb cleaner thru the bores they came out of, if you have access to a compressor, blow them out after the spray. This is best done with the carbs off the bike....

[Dan Filetti]

Surprised no one has mentioned that an intake leak, (this is my bet) can easily be tested with spraying starting fluid in and around the intake boot area etc. -if the idle rises, you have just confirmed that there is a leak, if not, you have fairly high confidence that you have dispelled it.  Be careful, too much starting fluid in and around the hot motor can be dangerous...

If the above does not yield a diagnosis, next, as Andy says, I'd read the plugs.  If they are light/ white, you DO in fact have an intake leak of some sort. If they are dark/ wet, then you're rich, (and not in the good way).  Did I mention that I'm guessing this is in fact an intake leak?
   
Dan

[Seanextra]

As Dan pointed out do a spritz test as i like to call it ! First check all clamps and bolts on itake side check throttle cable is free and not binding then:

Get some WD40 or similar much safer than Starting fluid, anything like it will do like RP7  pretty much any corrosion / water dispersant spray. Then start the bike, start on the number one intake at the head-intake rubber O-ring area use the straw applicator to get direct "spritzes" of the spray on the area suspected of a leak usually a drop in revs or change in idle smoothness will signify an air leak work from left to right trying to spray all around the seal tested and then try the carb side of the intake rubbers. Dont forget to check the Balance Tube Rubbers the little ones blocking off the the Balance Guage pipe fittings these may appear like new but leak like the proverbial Barb Wire Canoe.

If you find even one leak no matter how minor fix it ! and do all the other 3 at the same time, easiest way around it is if they are dry or slightly hard cracked rubbers just fork out for a new set they will be good for another 20-30 years!

Rolls and Loops

[racerman_27410]

i'm going to go out on a limb here and suggest lowering the idle via the idle adjuster screw.


there may be a leak but if you just got finished synching the carbs then its possible the idle screw was in too far to begin with.


KISS  (keep it simple)


KOokaloo!

[Sideburns]

any luck?

[David Allaband]

Thanks to everyone for all the advice!

I got a bunch of parts from RPM and put them on yesterday. I put on UNI pod filters and changed the jetting. I only started it for a minute but the bike ran perfectly! I'll have to warm it up and ride it around to see if the problem is still there. I had trouble in the past with the idle jet so the new idle jets might have fixed the problem more then anything.

More to come when I ride it!