Carb question.....

[BA80]

Back from test riding, mostly Interstate. The re-adjustment made the difference! Seems happy at 4turns out on mixes. Think I'm out of those just a tad beyond highest in.vacuum, as plugs are dark,dark brown down inside with a tannish brown electrode.
Previously, at 2 1/2 turns out, down inside plugs would be black,black with a white porclien/electrode out on the 'slab'. That also left it at a low 14in. of vacuum at idle.
These later model carbs sure don't seem to follow the 'rule of thumb' that if idle mixes are beyond 2.5 turns out, steppin' up the idle circuit is needed.

I may or may not fine tune those idle mixes to just EXACTLY when highest in. vacuum is reached. A tad on the rich side runnin' in these hot temps sure isn't gonna hurt my feelings going to and from the rally. If it looks like it's bothersome down in the pilot circuit runnin in the higher elevations, I'll have the MorganTune with me anyways for any changes.

What's curious to me, is why the rich cond. with the lean settings and corrects itself setting idle mixes richer, which in turn maximises vacuum?

Brant, you might go I size up on the pilots. Opening the mix screws actually will richen the mid range slightly. That might be what it's begging for.

If it's running a bit rich on the highway it might be because you have to crack the throttle a little and scavenge the mains to get it happy. I'm running 1 size over on mains and pilots and I'm still a tick lean with my Mac exhaust and the
older style carbs.

I really dislike the late carbs, they were designed to make OSHA happy not the engine.

[motoman]

Brant, you might go I size up on the pilots. Opening the mix screws actually will richen the mid range slightly. That might be what it's begging for.

If it's running a bit rich on the highway it might be because you have to crack the throttle a little and scavenge the mains to get it happy. I'm running 1 size over on mains and pilots and I'm still a tick lean with my Mac exhaust and the
older style carbs.

I really dislike the late carbs, they were designed to make OSHA happy not the engine.

That was kinda a random thought of Scott and I's when Scott was here last fall. Even though having the foam UniFilter, which I've left 'dry', un-sprayed with PJ-1 at this point is the only what you might call a 'mod'., just didn't really see that as requiring steppin' up the pilot's circuits needs. I have come to know with all the experimenting, some accidently, if that pilot circuit is not spot-on with the later carbs, it screws with all the rest of the fuel circuit.
At a 4-5000rpm cruise, a quarter turn either way of the mixture screws changes plug coloring drasticly, the tone of the exhaust and head-pipe sound.

BTW, it was all but puking on itself gettin' up PikesPeak behind 5-10mph traffic. Had to lag a little behind vehicles approching switchbacks, then rev into the main circuit, slippin' clutch and slinghot around switchback......kinda reminded me of moto-x style. It made the 14,100ft......but a struggle for it. Was expecting it on that ride, so no biggie.

[BA80]

The mix screws are IDLE MIXTURE SCREWS not running down the road mixture screws. They may make a small difference if they are WAY out of adjustment at cruising speed but a couple of turns out will RICHEN the pilot circuit, not lean it out. The idle mix screws control fuel flow to the idle circuit out being richer, in being leaner.

The Idle circuit has very little to do with anything but closed throttle operation but it does still come into play slightly as it IS part of the pilot circuit.

Rule of thumb, and I am absolutely against counting turns other than as a preliminary setting before tuning, is if you have to open the mix screws more than 2 turns you need larger pilot jets.

[motoman]

Understand that tottally Greg. Only area I see we dissagree, is that the idle/pilot circuit plays a bigger part overall than one may think throughout rpm range. The plugs verified that. As you know, venturi velocity determines the additional need for fuel, which is then ADDED to the already max. out pilot circuit via the larger main circuit. In other words, if pilot circuit is rich, main circuit doesn't know that. It just adds what venturi velocity demands(straw in glass of water, blowing across it).
The cross-over tunnel on the early carbs had that solved, but didn't make EPA happy..........made you happy, as they are more forgiving when it comes to final tuning.

[BA80]

Reread my post...........s-l-o-w-l-y

http://home.everestkc.net/malsin/Motorcycle/carb/mc_carb_theory_101.htm

[3Phase]

Brant, now that the Ignition wire's been fixed does the engine hang after revving the engine at idle (lean or carb sync SNAFU) or does it drop low and come back up to idle (rich)?


Greg,

I'm thinking about shipping a set of carburetors to Clifton just to see if the ignition system is having fuel problems or if the fuel system is having electrical problems.

The Pilots jets are possibly a little too rich because it's spitting under load off-idle, needs a little extra clutch and RPMs taking off from a stop but then it puts out slightly black smoke and blackens the spark plugs at low speed. That's the transition ports' range and those aren't adjustable at all except by changing the fuel and air jets. Following Brant at the rally made my eyes water even more than my bike that was spewing its own unique clouds of different color smokes.

There was a loose Ignition wire in the Fuse Block but CaptonZap fixed that in a Wendy's parking lot and it didn't eliminate the problem, it just made it sputter a little more smoothly and need a little less clutch and extra RPMs taking off.

.

[BA80]

I'm fixin' to ride over there and eliminate the damm problem.

I had a hell of a time with these carbs when I first got this bike and I went through every mistake that can be made I think.

Settling on the early style carbs relieved my migraine. But that's just me.

Doc ( RockinD) gets HORRIBLE gas mileage but his bike runs great. (late carbs). I had those things apart ________ times and they are freakin' perfect as unadjustable carbs can be. riding with him he has to stop for gas before my warning light even comes on.

I HATE late carbs, they do whatever the f__k they want.

[motoman]

I know it used to be happier, even though not quite there with float static levels at 23mm WITH gasket in place. That transferred to just a 'tick' under 24mm measured without gasket in place.
But, with unknowing gradual voltage loss over time, I was just tunin' it to a growing weaker spark.
The first clue to that, looking back a few yrs., should of been the Alpine stereo shutting down when coming to an idle. Looking back, there were alot other tell-tale signs that in the future I'll better recognize.
Reading thru that link(thanks BA80) reminded me of what I always did in the automotive world pertaining to carbs. Living at 6,500ft. elev.(Durango,Colo.), I always set float levels 1/16" lower than specified. Factory specifications are sea-level specific, including timing.
That may or may not relate to bikes better running, even though it was hiding electrical/ignition issues.
Scott, it acts normal from a high rev snapped back to idle.........immediate 1100rpm with no fluxuation/variation........even up the Peak after a rev that never cleared anything, you'd think it woulda choked enough.....then dropped immediately to idle, would of loaded up enough to die. Was wierd, it would just idle perfectly smooth like a mixture/sync session had just been done on it. Obviously, it was a bit 'soggy' on the high-end. The lower down we went, the better it ran. Even 1000ft. changes in elevation up and down that hillside country was noticable how it ran.

[motoman]

Not to get off track, but a local neighbor nearby, whom I've sync'ed his carbs on his 81Special, and still has the factory tin caps in the mixture screw recess and all was needed to bring his concerned low idle of 900rpm back to 1100rpm was to bring the pairs back together. That bike does run good, no matter what rpm range....all stock and original cept for the black color being changed to red.
It would be interesting to know just what exact level those floats are and mixture settings, since mine are 81Special carbs. Only problem........it would cost me $800 to find out...........yea, it's for sale.

[3Phase]

Greg, I know exactly what you mean but shipping's still semi-sort-of cheap and the ~100 fuel cost from Tulsa and ~35 from Simi to Grand Junction would take some of the fun right out of watching Brant work.

Brant, I forgot to bring the XJ carbs to the rally this year -- d'oh! See if you can borrow your neighbor's SH carbs without buying the entire bike!

I've almost got my own bike torn down again but after fixing the VF coil primary wires on your bike and a couple of days cleaning that Green Goddess dressing/windshield adhesive out of the carbs last year we never did get to try the carb swap once your bike was up and running. We didn't really have the time to do the work again this year but I would have just left them at your place and let you see if they got rid of the stutter and black plugs or made it worse!

.

[motoman]

Just bumpin' this thread along a bit..........curiosity finially got the best of me.....staring at the still loaded down Bentley after the Colo. rally.

I rocked it up on centerstand, putting a small piece of thick rubber belting under the right leg of centerstand to have carbs perfectly level, and a little sliver of wood under front to level for and aft.

To back up a bit, so those interested don't have to go back and read, just prior to rally, did a 'final' COMPLETE dis-assembly of carbs at time, and cleaned EVERYTHING. At that time, I also 'corrected' the float levels from my long ago setting of 23mm WITH gasket in place, to 23mm WITHOUT gasket in place, with a slide dial indicator(.905....)
Didn't see a problem with that............until now.
Not sure yet is it's any concensuses or not, but I turned fuel onto PRIME to replentish the fuel lost to the hose. NOT running, staticly, the actual bowl fuel levels, on ALL bowls is 9mm down from carb body casting.....nowhere close to 3mm. That's right at the bottom, or head of bowl retaining allen bolts.
I'll have to re-check those levels with it running(as stated for ALL 81 and XJ models) for any noted change.
Even if that comes up some while running, that explains the rich cond. Throttle plate openings have to be slightly more open in order to draw the TOO low a fuel level, which incorrectly draws too much venturi vacuum across the three ports, allowing too much fuel, from the increased venturi velocity, which follows with 'throttle plate openings control fuel flow, not engine speed'. Sound reasonable?
I'll get to the runnin' fuel bowl levels sometime soon......just wanted to update a bit for anyone interested.

[3Phase]

Have to think about it for a while... okay, I think you were doing better with that XS11 version of the 100 MPG carburetor that uses water for fuel: looked good on paper and the glossies were keen.

Set the fuel level in the float bowls.
Synch the carbs.
Set the mixture screws.
Leave the carburetors alone.
Keep fresh fuel in the tank.
Ride.

Or you could get an ST11.

.

[motoman]

Have to think about it for a while... okay, I think you were doing better with that XS11 version of the 100 MPG carburetor that uses water for fuel: looked good on paper and the glossies were keen.

Set the fuel level in the float bowls.
Synch the carbs.
Set the mixture screws.
Leave the carburetors alone.
Keep fresh fuel in the tank.
Ride.

Or you could get an ST11.

.

Think your on to something.
Definitely way too easy to just put the XS on 'ignore', throw a leg over the STeed, turn the key, and ride as far as the grin will carry ya'.........surely it can't be from lack of persistance........but it'll have to wait till after the cage adventure to GA. and back.......next month will keep me consistantly consistant.

[3Phase]

.......next month will keep me consistantly consistant. Meanwhile, might accidently slip, and find myself checking running fuel levels, just to break the the consistancy pattern.

Have fun in Georgia! and don't light The Bentley on fire futzing with the float bowl fuel levels!

.

[motoman]

Have fun in Georgia! and don't light The Bentley on fire futzing with the float bowl fuel levels!

.

No problem.....I do it on a 'cold' start, leaving enricher on first step since fuel level is constant no matter where it's drawn to.
Did it hot a few yrs. back and didn't like so much the sizzle on the pipes from a few drops of fuel from removing the hose hitting them. Fortunately, the fumes and air mixture wasn't correctly metered.