warm fluctuating idle

[ninjaneer]

so i've been trying to figure out a problem with my idle. when the bike's cold, it idles great. but after it warms up, it starts hunting, meaning it'll rev up to like 1500 or 2000 for a second or two and then drop back down to 1000 for some random number of seconds before revving back up to 1500/2000. there is no periodic behavior, meaning, for example, it doesn't shoot up for a second then drop back down for a second--it purely has random dwell times. i found out accidentally, that if i forcibly twist the throttle past its natural "idle" position and hold it there, this fluctuating idle problem disappears.

i've googled the 'net and everything seems to point to a vaccuum leak, but i'm not really convinced because all the talk was about carbs or efis or mapi sensors on cages--nothing related to a set of motorcycle carbs.

i recall reading ZackDaniels' recent throttle post and ran across his question about the throttle cable junction box under the scoop. i'm thinking that because i'm able to remedy the situation by twisting the throttle past the natural idle position that perhaps their is a linkage matter. i've futsed with the cable slack, but not without joy. perhaps there's a cable matter inside this push/pull junction box? or perhaps where the push/pull throttle cables attach to the carb rack? i don't know.

i'm running an S7 setup, btw.

please deposit your two cents

 

[tugla]

id disconnect at the throttle block and run the bike.....see what happens and also how is the sync on it.....
couldnt hurt to take the propane torch and blast the intake boots and joints with gas and see if idle changes incase there is a new leak .

last carb cleaning was???

 

[Miles Long]

Manually working the throttle directly from the carburetor linkage would point to cable and/or linkage problems, IF idle response is normal - no "hunting" up and down.
Cheers!

 

[ninjaneer]

how is the sync on it.....

spot on, i synch every other month

last carb cleaning was???

maybe 10 months ago?

thanks so far for the tips Miles and tugla

 

[jfeagins]

Nothing in your linkage would cause it to go up and down randomly. It'd be stuck up, then return down AND STAY THERE, or it'd be stuck up and NOT COME DOWN EVER.

I'm betting an internal carb issue - perhaps with a float level, so that when that carb float opens up, and the fuel level returns to it's uppermost level, that carb is putting more idle on through to the awaiting cylinder and making the RPM's go up. Float closes for a bit, and fuel level begins to drop dangerously low, affecting RPM. If a float works correctly, it'll be keeping that carb level pretty much even at all times, and the carb settings you have on that carb perform seamlessly, otherwise..... Perhaps you have a sticking carb float?

I'm just sitting here running carb physics through my brain out loud....and I'm not seeing where an air leak would run the idle up and down randomly either. But what I know could prolly fit in a thimble.

 

[[email protected]]

Disconnect throttle cables either at the grip or at the junction block to eliminate cable as an issue.

If still hunting up/down, check for air leaks. Cracked rubber or something not seated properly.

If not a cable issue and if not an air leak then.......?

 

[jfeagins]

Perhaps low voltage at idle causing the BlackBox to act up?

 

[bazwell]

The thing where you are forcing the throttle is most likely masking the problem, not fixing it.
It's like a slow PC due to a corrupt registry entry. If you defrag and virus scan it will seem a little better, but it's not pinpointing a problem. :biglaugh:

It's probably a very small vacuum leak.

 

[ninjaneer]

alright folks, so i went down this route to hunt down the leak. call me cheap, but i had a pack of smokes more readily available than a can of ether or propane.

http://www.youtube.com/watch?v=zMok2y05jNE

I popped off the my indy filter pods, stretched some latex glove over the velocity stacks fastening them down with rubber bands, popped off synch port "H" covers, and one at a time attached one of my Carbtune tubes to a synch port nipple and blew smoke into it while plugging the associated fuel vent tube.

Low and behold smoke started trickling out of carb #3's AFR adjustment port. I pulled out the screw, and found the o-ring a bit folded in itself, so finagled with it a bit, shot some carb cleaner through, buttoned her up. I reckoned I should go ahead and clean out the other carbs and found the o-ring on #4's AFR adjustment screw was missing its o-ring. UGH. BUT when I blew smoke through the carb, no smoke escaped from anywhere. #1 and #2, both had complete AFR adjustment assemblies and no smoke escaped as well. hmmm. anyways, for the past couple of days, knock on wood, the surging idle has disappeared. however, the idle is slightly bouncy and not as rock-solid steady as i have seen other's doing. perhaps it's because i have a stage 7 setup? or perhaps it's because #4 is missing its adjustment screw o-ring? i wonder if #3's o-ring was not properly seated, kind of bent or pinched or something allowing smoke to trickle out. this could explain why i have had so much difficulty adjusting the AFR by ear (listening for the motor to stumble and then backing out the screw until it recovers)?

Time will tell, I suppose.

I'm going to hunt down an adjustment screw assembly for #4 in the meantime.

 

[[email protected]]

Kick ass idea.

 

[ninjaneer]

yeah mike, i like this approach alot, cuz you actually see the leak, as opposed to ether or such just pointing out a general area. imagine, if i sprayed propane or wd40 around there? i dont know if i would have zeroed in on the afr screw so quickly. its hard to know what i would have diagnosed otherwise, but i could have easily changed out a boot or rebuilt the carb or something requiring tons of downtime and/or dollars and not fix or never know the prob

Regards from my Taptalking Hercules Android

 

[bazwell]

Brilliant!
All the non smokers can suffer fluctuating idle.unk:

 

[94 V-Max Rider]

My brother's 2007 Max does the same thing. The idle fluctuates momentarily when hot and does it very sporadically. The bike only has 8k on the odometer, but he bought it not knowing it had been re-jetted (overly rich). I've had the carburetors out twice to correct the jetting. In doing so, I took the time to clean and inspect everything carefully. I've found nothing out of the norm. I've tried catching it in the act, but it seems impossible given its quick and sporadic nature. If a problem existed in the throttle junction, I suspect it would act up at any time.

 

[ninjaneer]

so it's been a little over a week ( about 250 miles) since i blew smoke into the carbs and re-seated the french-inhaling #3 o-ring. the idle doesn't jump up and down anymore. the tach needle now just slightly trembles around something like between 1000 and 1050 RPMs, but all the time, not like the freakish jumps to 1500 for how ever long every how ever minutes. this i can live with. am waiting on a pilot screw assembly for #3 and #4 before i continue the chase for the super steady hum. i'll blow some more smoke (this time with a cigar for volume) and see if there are any more leaks after rebuilding the AFR screws, a shotgun/peashoot and resynch are in order as well.

 

[ninjaneer]

the pilot screw assemblies finally came in. i got one to replace the bent one in #3 and the apparently missing one in #4. i say "apparently" because when i shot a puff of air into the carb to get the washer out came these


i peashot and shotgunned the carbs, verified the synch, and dare i say, i'm back in business. maxxy idles a heck uvva lot more consistently now.

if i remember to, i'll get me a romeo&juliet the next time i'm buying a bittle of tequila. am not gonna go iutta my way for cigar. am perfectly content with what ive git at the moment

Regards from my Taptalking Hercules Android