CARBS HIGH IDLE - COULD IT BE SPRINGS ??l

I just rebuilt the carbs on my wife's 1981 XJ550 Seca and the idle runs away on me. I'm a novice mechanics and the only thing i can guess was when i re-connected the springs between the carbs i should have wind them tighter. I believe after taking them off for the second time it's the only thing possible. I believe they spring back adequately and i don't want to over wind them and brake them or have a hard throttle. Any and all help/suggestions appreciated.

 

You can't normally over tighten those springs, if you try to turn them another 360 deg they go all out of shape.
Did you take the buterflys off? they can stick & cause the runaway revs, also the trottle quadrant can get caught up, the bolt on the carp boot can cause this.

 

I didn't take off the butterflys , but i thought about giving them a squirt of WD-40. Would that be good. What's a throttle quadrant? What is a bolt on carb boot?

 

It's a pretty common mistake to have the Carb Linkage get held open by a Clamp or the Throttle Cable Connection on the Linkage.

If the Throttle Cable Connection is Jammed ... remove the Carbs from the Manifolds to free it.
Don't try to pry it or bend it.

 

Also check that the throttle cable is adjusted properly (i.e. not holding the butterflies open). You can also turn down the idle.

The slides can be sticking - do they go cluck (usually this is evidenced by a hanging idle after blipping the throttle - but I thought I'd mention it anyway)?

Also, as a multiple point failure (after you rule everything else mentioned here out) if extra fuel is getting to your carbs (enrichment circuit not closing, flooding in the bowls, pilot circuit set WAY too rich, etc) AND you have an air leak, the engine can rev and feed itself even when the butterflies are closed (because it is getting the EXTRA fuel, and the air it demands from the leak).

 

I can't see how the linkage can be affected if the clamps are where they should be but i'll triple check that. The throttle and choke cable are as smooth as silk . I brought the idle down real low and when i bring it up higher so does the run away some times 5,000 rpm's. I can get it to go down half the time by blipping the throttle or when riding putting a load on the engine or braking while in gear. I will check the slides but when i rebuilt them they dropped well. I have new intakes and gaskets for great seal. I did only set the air/fuel pilot mixture screw to factory setting. I was planning to use a new Gunson colortune once i got everything to settle down. Do you think the pilot setting is way off and i should do that now?

 

IN ORDER:

Valves in spec?

-Bench sync; check float levels using gas (the "clear tube" method.)

-Running vacuum sync

-tweak mixtures (Colortune)

Repeat vacuum sync and retweak as necesssary.

And NEVER EVER USE WD40 on your motorcycle unless it's to remove bug splat. It's dangerous as a lubricant, it gums up quickly with exposure to heat.

 

With the bike running, set the idle to 1000 rpm. You may have to blip the throttle to get the linkages to set - so do that and be ready to shut it off if it races. My experience after putting carbs back on - if the idle is accidentally set too high (like 3000 rpm) the engine will take off and be kinda scary, turning it down to it's appropriate spot will magically stop that issue.

Follow Fitz's advice...this could just be a fine tuning problem. Make sure you START with the valve check if you haven't already done it. As you do your running tuning, keep the idle down to 1000 rpm. It may increase as you make adjustments...because the engine is running better and more balanced.

What did you replace when you rebuilt the carbs (just to make sure we are on the same page)? And search the site for the slides going clunk. You can sand and polish the bores to the slides drop like a TON of bricks. No chattering or hydraulic action. The slides control fuel/air mixtures past off-idle, so if they stick, the engine will get too much air/fuel, even when the butterflies are closed.

 

Set the Throttle Cable Adjuster to provide SLACK to the Throttle Cable allowing the Throttles to CLOSE.

With the Throttles Closed ... Adjust Pilot Mixtures to IDLE.

The Throttles NEED to be Closed for LOW rpm's.
Once the Throttles are cracked and you let-in AIR ... the Engine is going to thank you and run faster for you.

 

I've done everything 3 times now. The slides are as smooth as silk and i used the colortuner only to find only one carb needing the finest of adjustment and they are all the perttest blue you could hope for. I'm somewhat reluctant to mess with the pilot screw adjustment at this time, but nothing is out of the question. I would just want to see if it's something else before i go back and mess with this because she's running like a stallion.
I can tell you this; The throttle stop/idle srew has the most tempermental adjustment. If i go much past 1,000 RPM she want to race to 3,000. Does anyone know what i might be missing that involves the corrolation of this adjustment and the run away throttle/idle? She runs so sweet on the road. This bike is new to us and i must say we want to keep her. My wife was running this bike around corners and accelerating on the ass end of my 750 Honda like no tomorrow. I took it out this morning and can attest this bike must have been way ahead of it's time in 1981.

 

The ColorTune Plug does NOT differentiate between Pilot's Running the Bike and Throttles sneaked-open providing a nice Mixture of MAIN Jet Fuel and Air.

When an Ideal Air~Fuel Ratio is present ... it's Blue.

YOU have to:
Back-off the Idle Adjustment Rod and Slack the Throttle Cable so the Butterflies are CLOSED.

Then, ...

You get Holes 1, 2, 3, & 4 to IDLE the Bike by Adjusting the PILOT Mixture Screws to where the Air-Fuel Ratio is best to sustain IDLE.

THIS ... is why the ColorTune Plug was invented.
Using the ColorTune Plug, ... you can FIND --> WHERE <-- the Pilot Mixture is BEST to sustain IDLE.
The ColorTune Plug lets you see where the Mixture Screw NEEDS to be ... to provide a marvelous Air-Fuel Mixture that will allow the Bike to IDLE.

Once you have the Engine IDLING without introducing Fuel and Air via Throttle Opening ... you are HALF WAY THERE.

Now, ... You MUST continue Adjusting the Pilot Mixture Screws to SUPPLY the Engine with a LITTLE BIT >> M-O-R-E << Richness to SUSTAIN Combustion for that BRIEF ...

BRIEF ---> About 3 very-rapid eye-blinks

instant where the Throttles are Opened and Intake AIR rushes-in to the Combustion Chamber.

Supplemental Richness!
NOT Blue.
MORE than Blue.

Extra FUEL to Mix with the eye-blinks of Fresh UNFUELED Air that rushes in to the Cylinder before the Main Jet Supply kicks-in.

Not pretty Blue.
Just pretty Blue ain't enough.