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Discussion Starter #1
...since it's just me replying to myself, it looks like no one is reading it as new material. So sorry to do this, but I'm starting a new thread because I sincerely want to get to the bottom of this. This is a hijacking of my FCR tuning for laymen thread (typo o in the title is noted):


I'm hijacking my own thread. I'm about to pull my hair out.

Is the "it's lean" in the pilot circuit that causes the hanging idle a hoax?

Is the "it's rich" in the pilot circuit that causes the hanging idle a hoax?

While waiting for my jets and needles to arrive, I thought I'd take the time to exercise the adjustability of the FCR carbs to futz with the hanging idle issue as various persons in various posts on this topic (reference specifically the pilot jet, the fuel screw and the slow air screw) said that with the fuel screw and slow air screw, you should be able to adjust most of the lean/rich condition out of idle and at low throttle settings, and that if not, only then do you go to a larger or smaller pilot jet. Makes sense.

I'm having the hanging idle issue too where the RPM comes down from wide open throttle to around 3k or so, then hangs for a second, and then slooooowly creeps down to idle over three to four seconds.

Most pages I've visited (to include the FCR tuning pages) says that hanging idle is indicative of a lean condition in the pilot circuit. AND also most pages I've visited inexplicably says that a smaller (leaner) pilot jet would help (diametrically opposing concepts)... go from a 60 pilot, say, down to a 52 pilot. So the problem is both a rich and a lean problem at the same time? Haha.

If it's a lean problem, why go leaner with a smaller pilot jet? But it's so prevalent that people go with smaller pilot jets for the FCRs with Supersports and Monsters that all the kits available (if you want multiple jets to experiment with) come with 60 and smaller pilots. If you want larger, you have to order them individually.

Then, just to keep me on my toes, duc96cr said "You can probably just adjust the air screws enough to fix this. You need to screw them out a full turn at a time and try it. As long as the screws still effect running, you haven't run out of adjustment."

That says go leaner, not richer.

And pajazo said, "What i'm saying is that the hanging throttle with ducati & fcr's is not actually caused by a lean condition as the common wisdom says, but can indeed be circumvented by tuning the idle mixture very rich."

That says go richer, not leaner.

Joe-B says, "A hanging idle would point towards a lean slow mixture (idle) setting."

Anyway, going with the prevailing wisdom that hanging idle is caused largely be a lean condition in the pilot circuit, I pulled the pod filters and the carb adapters from the FCRs and validated that the slow air screws were both indeed set at 1.5 turns out per standard staring point, and then turned them to 1 turn out, which should richen (less air) the mixture. I also have the fuel screws turned out to 3.5 turns which should richen (more fuel) the mixture. That should be VERY rich with those settings. But WTF? Made the idle hang way worse! I had to turn down the mechanical idle speed screw to make it idle at around 900 RPM to make it settle. And the engine runs a tad rough at 1/8th to 1/4th throttle.

I'll probably follow NoneMoreBlack, who said, "I kept the air screw at stock setting (1 1/2 turn) as any messing with it gave really bad results..."

But duczilla suggests, "Pull the bowls. Pull the pilot jets. Blow some air thru. Read the number on the jet. Get a size larger. Install. Put fuel screw back to around 1 turn and go from there. Fixed." So go richer on the pilots.

And from a guy that I have used regularly to fix some of my problems, 944SS (thanks, mate! I have a FE as well!), "Maybe a fix for the hanging idle but in my experience it kills the off idle throttle response at least for those of us running near sea level like the OP. I am running 52 pilots and they work a treat. No significant hanging idle as long as you keep the idle speed low." So go leaner on the pilots.

Later, NoneMoreBlack spells out one of my points of confusion rather well when advised go smaller on the pilot jet, "Stock slow jet is 60. Wouldn't this be insanely lean, if I am already facing a lean issue? I was planning to purchase 62s."

Why this diatribe? Someone will likely say, "Hey fucking idiot, if richening it makes it worse, go the opposite direction.

Well, I'd like to have someone weigh in that actually literally knows the physics behind the hanging idle and clear this up once and for all. Probably need a sticky with the actual answer as this is literally 50/50 across forums as to leaner/richer in the pilot circuit area with contradictory information. I've searched every supersport and monster forum where FCRs (39 or 41) are mentioned, and it's the same. Lean causes hang. Richen it with fuel screw and/or air screw. Pilots too big, go smaller. Lean it out. Pilots too small, go larger. Richen it.

Will someone PLEASE clear this up. I'm obviously going to go the opposite direction later this evening and see what happens. Frankly, it seems to me that after well over a hundred years of carburetion with no hanging idle on most gas burning machines the answer to this puzzle would have been solved by now.

Thanks
 

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I fixed my hanging idle by taking it to someone who actually knew WTF they were doing and paid them. The carbs run exponentially better, but still hang when cold.

Part of the issue is the lack of choke and compensating with the idle speed adjuster. Remember, these are race carbs, not street carbs, and as such have some additional TLC they need to make work.

I believe he issue is not due to a lean condition in the carb, but a lean condition in the cylinder; all the circuits on the FCR affect all the other circuits to some degree and while some should be negligible, the effect isn't a true 0. You can't think about it as troubleshooting a single point, but think holisitically about what you're doing and how it effects what's coming out of the back of the carb. The pilot bypasses the main circuit when the slides are completely closed ... but we open the slides with the idle control knob to control for idle speed, so even though minimal, the rest of the main jet, clip, and needle profile are still contributing to the final mixture in the cylinder. With the needle that low in the main nozzle, we're probably adding more air than fuel, causing a lean mixture in the cylinder when combined with the properly targeted pilot circuit ... and hanging the idle.

I find the hang is a function of carb throat temperature and idle control position. When the bike is truly cold having sat overnight in the garage, I crank the idle control up a full turn, pump the throttle twice to dump fuel in the cylinder as an enrichener, then crank the bike. If it stalls out quickly, I'll add another 1/2 turn to the idle speed, pump once and try again. Once it catches it lugs along at 1000 RPMs or so until the throats start to warm up, then jumps up to 3K. I back the idle control off until it comes back to 1200 or so, and another minute or two later, it jumps back to 3K. I pull it back to 1200 a second time and ride away. By the time I get to the first stop sign in my neighborhood it's hanging at 3K again and I pull more idle speed out to get it back to 1200 and depending on the ambient temperature, that might settle it down for the remainder of the day, or I might need to adjust idle speed one more time.

In the dead of winter, in my garage that is at the mercy of ambient temps, I can't get the bike to start at all under 40 degrees F. If I do want to start it up, I crank up the garage heater for an hour, or take a small space heater and point it at the intake runners for a few minutes.

PS - I'm hoping a mod merges this back into the original thread. Don't take it personally, one of the main reasons this forum has such low signal to noise ratio is by being patient.
 

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imo, part of the issue here is interaction between carb and ignition system. well, possibly compounding the issue is the more appropriate term.

with the single step advance, the engines will hang onto that advance down to 2,200 or so rpm. if you have enough throttle opening to idle at 1,200 with 6 degrees advance, that's nearly enough throttle opening to idle at 2,500 rpm with 36 degrees advance. if the mixture is too rich, as the fcr are ime with the 60 pilot, you end up with the idle stop wound in more to make them idle and overcome the too rich. this in turn makes them susceptible to holding up as the rpm drop.

if you had the idle mixture set nicely and confirmed that mixture as say 5% co and clean, then the idle stop setting required to make it idle happily will be further out (lower) than if it's too lean or too rich requiring the slides to be lifted to compensate.

some somewhat irrelevant examples.

bevel drive with a too small pick up gap will advance the timing at lower rpm than desired. once revved up, as the rpm fall they will not drop far enough to lose that first step of advance. so you wind the idle stops out a touch and it suddenly loses the advance and drops from 1,800 to 800 rpm. solution is to remove the clutch cover and increase the gaps.

guzzi breva series motors will hold up the idle when closing the throttle at say a set of lights. you get into the ecu file and take the ignition advance at closed throttle out from maybe 2,200 rpm down to a bit above idle. fixes it instantly. they probably taper the advance down from 25 degrees at 2,500 to 10 or so at idle (1,200 ish). to fix them, make it 10 from idle to 2,200 rpm.

then there's also the issue of the push/pull cables. some people adjust the push cable to have little free play, and that can make the throttle not snap shut. first thing i do is put a heap of clearance into the push (return) cable. also common with the std mikuni carbs.
 

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Discussion Starter #4
I fixed my hanging idle by taking it to someone who actually knew WTF they were doing and paid them. The carbs run exponentially better, but still hang when cold.

Part of the issue is the lack of choke and compensating with the idle speed adjuster. Remember, these are race carbs, not street carbs, and as such have some additional TLC they need to make work.

I believe he issue is not due to a lean condition in the carb, but a lean condition in the cylinder; all the circuits on the FCR affect all the other circuits to some degree and while some should be negligible, the effect isn't a true 0. You can't think about it as troubleshooting a single point, but think holisitically about what you're doing and how it effects what's coming out of the back of the carb. The pilot bypasses the main circuit when the slides are completely closed ... but we open the slides with the idle control knob to control for idle speed, so even though minimal, the rest of the main jet, clip, and needle profile are still contributing to the final mixture in the cylinder. With the needle that low in the main nozzle, we're probably adding more air than fuel, causing a lean mixture in the cylinder when combined with the properly targeted pilot circuit ... and hanging the idle.

I find the hang is a function of carb throat temperature and idle control position. When the bike is truly cold having sat overnight in the garage, I crank the idle control up a full turn, pump the throttle twice to dump fuel in the cylinder as an enrichener, then crank the bike. If it stalls out quickly, I'll add another 1/2 turn to the idle speed, pump once and try again. Once it catches it lugs along at 1000 RPMs or so until the throats start to warm up, then jumps up to 3K. I back the idle control off until it comes back to 1200 or so, and another minute or two later, it jumps back to 3K. I pull it back to 1200 a second time and ride away. By the time I get to the first stop sign in my neighborhood it's hanging at 3K again and I pull more idle speed out to get it back to 1200 and depending on the ambient temperature, that might settle it down for the remainder of the day, or I might need to adjust idle speed one more time.

In the dead of winter, in my garage that is at the mercy of ambient temps, I can't get the bike to start at all under 40 degrees F. If I do want to start it up, I crank up the garage heater for an hour, or take a small space heater and point it at the intake runners for a few minutes.

PS - I'm hoping a mod merges this back into the original thread. Don't take it personally, one of the main reasons this forum has such low signal to noise ratio is by being patient.
Thanks for the details, and technique. Though I appreciate the comedy of the voodoo chicken someone posted as a solution to FCR carb jetting, it's just not helpful. Yesterday I put the air screw back to 1.5 turns and left the fuel screw at 3.5 turns, and then cranked the idle adjuster up... and as I rode I adjusted it down... just as you described. It's livable for now. I have the EMR needs on the way. I'll make no changes until they arrive and I can install them. I'll start on the 4th clip position and go from there.
 

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Discussion Starter #5
The pilot bypasses the main circuit when the slides are completely closed ... but we open the slides with the idle control knob to control for idle speed, so even though minimal, the rest of the main jet, clip, and needle profile are still contributing to the final mixture in the cylinder. With the needle that low in the main nozzle, we're probably adding more air than fuel, causing a lean mixture in the cylinder when combined with the properly targeted pilot circuit ... and hanging the idle.
I know this'll sound silly, but you just gave me one of the biggest "aha!" moments since I started asking the forum for advice on how to set up the FCRs. No one has ever explained that to me. I've been scratching my head wondering how it could be possible that screwing the idle speed down mechanically could actually minimize the effects of the hanging idle. BUT, inexplicably, IT DOES!

Knowing absolutely nothing about carburetors, it never occurred to me that with the slides fully closed, the pilot bypasses the other circuits and runs the show largely independently (explaining how small adjustments to the fuel screw and slow air screw can have a fine tuning affect on idle).

I wind up the idle when starting from absolute cold.... the RPM is a tad low and sluggish at cold idle, but would drop fine when revved... then a block away, idle hangs... wind it down... then a block further, idle hang... screw it down... good to go... a block away, idle hang... screw it down. Eventually (as was the case last night), I have it wound down to full closed on the idle screw, engine idling at around 1,000 even and smooth(ish)... and the idle drop is mostly normal from any RPM.

I literally didn't know that by screwing the idle up from zero (slightly opening the slides), I'm essentially inviting the other circuits to the party. Then the mix trends lean, and idle hangs. Fuck me.

That is literally the best description of everything I have personally witnessed while adapting to these new carbs, and explains all of the inconsistent answers I've read across the forums (SS and Monster). It CAN be both rich and lean at the same time... depending on where the mechanically set idle is. Just turn the idle screw and see!

Hopefully the moderator will sticky your answer. It literally explains why I've been chasing ghosts for the last two weeks.
 

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the slides are never fully closed. if they were, there'd be no air going in. the pilot circuit provides fuel when the slide is low over the pilot outlets and thereby creating a vacuum over them as the manifold vacuum sucks air through the carb. once the slide is lifted the drop in vacuum causes fuel (and emulsifying air) to stop flowing through the primary circuit progressively as the slide is lifted and the needle jet becomes the primary fuel outlet.

having the slides too high at idle can cause issues with vacuum strength in the pilot circuit, and it can be noticeable how much richer they become when the slides are wound down, requiring the mixture screws to be wound in. that's why you need to get the idle mixture sorted, generally once you have the mixture sorted and the slides wound down for the desired idle speed things tend to flow from there. getting it sorted has been the issue i've seen when playing with fcr.
 

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Thanks for the details, and technique. Though I appreciate the comedy of the voodoo chicken someone posted as a solution to FCR carb jetting, it's just not helpful. Yesterday I put the air screw back to 1.5 turns and left the fuel screw at 3.5 turns, and then cranked the idle adjuster up... and as I rode I adjusted it down... just as you described. It's livable for now. I have the EMR needs on the way. I'll make no changes until they arrive and I can install them. I'll start on the 4th clip position and go from there.
The EMR will no nothing for your idle and/or warmup time. The needle called out per spec is the EMT, the EMR is slightly richer at 3/4 throttle and may or may not be necessary for your particular build. I have a dyno pull that shows it pretty clearly.

I know this'll sound silly, but you just gave me one of the biggest "aha!" moments since I started asking the forum for advice on how to set up the FCRs. No one has ever explained that to me. I've been scratching my head wondering how it could be possible that screwing the idle speed down mechanically could actually minimize the effects of the hanging idle. BUT, inexplicably, IT DOES!
That is literally the best description of everything I have personally witnessed while adapting to these new carbs, and explains all of the inconsistent answers I've read across the forums (SS and Monster). It CAN be both rich and lean at the same time... depending on where the mechanically set idle is. Just turn the idle screw and see!

Hopefully the moderator will sticky your answer. It literally explains why I've been chasing ghosts for the last two weeks.
I'm just some guy on the internet, take it with a grain of salt. I really didn't understand carbs until I got this bike and beat my head against the wall like you did. I am not a professional, I am not trained, and I do not get paid to work on motorcycles, and I still only barely understand carbs.
 
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