Carb question.....

[WMarshy]

...

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.

No, it does not sound reasonable to me. By resetting your float height to 23mm without the bowl gasket you increased the gas level in your bowl. The outcome will be a richer F/A ratio across the entire throttle range.

Air velocity in the carb is constant for a given throttle position at steady state (crusing at a given throttle position). The velocity in the venturi develops the vacuum that draws the fuel up out of the bowl. Velocity in the venturi is controled by the butterfly valve. If the fuel is lower in the bowl, less fuel is drawn into the venturi. Increase the fuel level and more fuel makes it into the venturi. Subsiquently RPM is a function of the butterfly position (volume of F/A) and not the F/A ratio being delivered. So, what Im trying to say is the butterfly will not compensate for a lean condition created by a low fuel bowl level.

[motoman]

No, it does not sound reasonable to me. By resetting your float height to 23mm without the bowl gasket you increased the gas level in your bowl. The outcome will be a richer F/A ratio across the entire throttle range.

Air velocity in the carb is constant for a given throttle position at steady state (crusing at a given throttle position). The velocity in the venturi develops the vacuum that draws the fuel up out of the bowl. Velocity in the venturi is controled by the butterfly valve. If the fuel is lower in the bowl, less fuel is drawn into the venturi. Increase the fuel level and more fuel makes it into the venturi. Subsiquently RPM is a function of the butterfly position (volume of F/A) and not the F/A ratio being delivered. So, what Im trying to say is the butterfly will not compensate for a lean condition created by a low fuel bowl level.

Wanna bet.......might re-read what you just stated sentences before..........BTW, opening throttle plates more to compensate for a low fuel bowl level screws with everything, including vacuum for correct slide operation at a given venturi vacuum............They gotta match, no two ways about it.
Also, the actual fuel levels are lower than they should be, not increased...
No offense, but you seriously need to re-read what's ACTUALLY goin on
Appreciate your input and discussion back and forth, but least get on the same page!

[WMarshy]

Wanna bet.......might re-read what you just stated sentences before..........BTW, opening throttle plates more to compensate for a low fuel bowl level screws with everything, including vacuum for correct slide operation at a given venturi vacuum............They gotta match, no two ways about it.
Also, the actual fuel levels are lower than they should be, not increased...
No offense, but you seriously need to re-read what's ACTUALLY goin on
Appreciate your input and discussion back and forth, but least get on the same page!

My only post in this thread, first paragraph, was to let you know that you increased the fuel level in your carb bowls dispite your readings and that higher levels will cause a rich f/a ratio, NOT a lean condition. Its not my theory, its fact. You even said you needed to recheck the numbers with the bike running. Maybe you should recheck the level.

My second comment was, velocity through a venturi determins the vac draw on the main jet and the pilot curcuit and the port to lift the slide. Velocity across venturi is in fact based on the position of the buterfly valve and relative to the engine RPM because RPM dictates the volume per unit of time. Because velocity causes vacuum which causes the slide to lift and meters the fuel from the main jet, the butterfly controls the circuit.

You dont have to Sh*t on me and say I have no idea of whats going on. I might have been born at night but it wasnt last night, I read the thread from the begining. If you have so much experience with carbs why cant you get your bike running right. The only thing I get from all your posts about carb theory are you have a good imagination but no clue on what actually happens inside because you make up some of the best half @ss theories on how you think it works. I think that is why you believe everyone has a secondary ignition issue. Good luck with your bike, I think I will keep my suggestions to myself when you ask.

[motoman]

RPM is a RESULT of butterfly position, not function. Butterfly position is a result of the right hand, period. Again, fuel flow, from venturi velocity is er determined by throttle plate opening, not motor RPM.
In a certain sense, we're saying close to the same thing, and true, a higher fuel level in bowl WILL richen ALL circuits. What I'm sayin' is a to low a fuel level in bowls can cause the same scenario assocciated with VACUUM slide carbs. So far, with an 800+ mile 'test run', that proves out to be true.....and ALL jetting/intake/exhaust are correct stock.

On a side-note, it's no wonder Greg favors the early carbs with the crossover, feeding BOTH circuits fully at all times......and a hell of alot more forgiving to a lesser than anal tuning. Thanks to EPA requiring more stringent emmissions control, the cross-over tunnel was eliminated.

[motoman]

Bonz's 80Special, which sport the same carbs as my Venturer, (which were swapped to 81Special carbs with the 5GL16 metering rods), has correct fuel mixture settings of APPROX. 1.5 turns out from seated, as opposed to mine being some 3.25-3.50 turns out to get any where near the highest in. vacuum. Setting them any where near the 2.25 or 2.5 turns out, which is the MOST they should EVER be out, vacuum across the four cyls. at idle drops to 14in.vacuum.
With max. vacuum at this elevation being 18-19in.vacuum, that's a far cry from the 18in.vacuum it normally would have. That alone is a tattle tale sign of either a to lean or to rich a mixture. In this case, with constant powdery black plugs, definitely too rich a setting with the idle/pilot circuit.

Good consenses of all this is the Honda VF coils fire those plugs,no matter how powdery black they get, and even now, after not starting for over a week, plugs blacker than sin, no enricher and it fires off almost before one complete revolution. Those coils make no more voltage than the originals did when they were new........but hey, Honda coils are notrious for not failing or fading into oblivion, even decades later.

[BA80]

RPM is a RESULT of butterfly position, not function. Butterfly position is a result of the right hand, period. Again, fuel flow, from venturi velocity is er determined by throttle plate opening, not motor RPM.

FUEL flow is determined by throttle position. At idle (closed throttle) the fuel ONLY comes from the idle mixture orifice, up to 1/4 throttle the fuel comes from the 3 small holes in top of venture through the pilot jet, 1/4 to 1/2 throttle the fuel comes from the pilot circuit and what is metered from the jet needle through the needle jet, 1/2 to 3/4 the fuel comes from the needle jet and the main jet, after that it's nearly all the main jet.

[motoman]

My only post in this thread, first paragraph, was to let you know that you increased the fuel level in your carb bowls dispite your readings and that higher levels will cause a rich f/a ratio, NOT a lean condition. Its not my theory, its fact. You even said you needed to recheck the numbers with the bike running. Maybe you should recheck the level.

My second comment was, velocity through a venturi determins the vac draw on the main jet and the pilot curcuit and the port to lift the slide. Velocity across venturi is in fact based on the position of the buterfly valve and relative to the engine RPM because RPM dictates the volume per unit of time. Because velocity causes vacuum which causes the slide to lift and meters the fuel from the main jet, the butterfly controls the circuit.

You dont have to Sh*t on me and say I have no idea of whats going on. I might have been born at night but it wasnt last night, I read the thread from the begining. If you have so much experience with carbs why cant you get your bike running right. The only thing I get from all your posts about carb theory are you have a good imagination but no clue on what actually happens inside because you make up some of the best half @ss theories on how you think it works. I think that is why you believe everyone has a secondary ignition issue. Good luck with your bike, I think I will keep my suggestions to myself when you ask.

As I stated, 'no offense', and never hinted to you not knowing what your talking about......quite the contrary. I just didn't see you quite following what was happening when I would set the idle mixtures to highest in.vacuum.......then on top of that, the static fuel levels were low(which I did NOT check before riding to rally). In the past, comparing the static and running levels, their is a very small amount of difference, but from past experience, that much of a spread from 9mm to the known 3mm setting, running mode, that level still will not even qualify being close to the 3mm.

My thoughts are to set those float levels to wherever that will put fuel levels in all four identically at 3mm down from upper carb casting, while idleing. That may correct not having those idle mix screws out beyond where they SHOULD be at less than 2.5 turns out, and still reach highest in. vacuum.

All I know at this point, is runnin' those mixture screws in a quarter turn, riding a few hundred test miles at rally on group riding, repeating again as it was still way rich(wonder why followers were so far back), and nothing changed, not even plug color, which at highway speeds should be white. They stayed black.......and a lousey 31.5mpg average over 800+ miles.
It normally always was a 38-41mpg@65-75mpg at those constant speeds.
Starting so immediately without using enricher on a cold morning outdoor start(at rally) is obviously a rich sign also.
Becoming curious as to actual fuel levels, suspecting they were a bit high after making the change from 24mm to 23mm(BTW, was the ONLY change I made after a final cleaning to eliminate any possible 'science project' that may have been lingering after the first two go-arounds(Scott tackled them the first time, myself the second time, and third final time). Finding fuel levels THAT low, even staticly, and the rich cond. associated, both circuits, is what has led me to surmise that even a to low a fuel level, requiring more throttle plate opening is not only killing mileage, changing color code of plugs, but ends up dumping to much fuel from the vacuumdraw required, from to much throttle plate opening.
Hope that makes better sense, as I don't half @ss anything, not even theories.

[motoman]

Another thought to ponder: The throttle plate opening being more, in order to draw the to low a fuel level more readily leaves a greater vacuum drop at the manifold than would be normal. This, I would think could cause the vacuum actuated slide/metering rod to rise more, and even BEFORE that ADDED fuel through the main circuit is actually required. I say added, cause that pilot circuit ain't got no shut-off spigot. It maxes out what it can flow based on venturi velocity from throttle plate opening.
More needed, based on venturi velocity then is added from main circuit....next least path of resistance to fill the increased manifold void, which was initially created from throttle plates increased opening.
The pilot jet tower, unless fuel levels are extremely to low is always submerged in fuel, and is at ALL times......least it should be or that circuit will be sucking air and whatever else thru the bowl vent. Pilot circuit doesn't just 'sit this one out' when main circuit comes into play.
A quick snap-rev to 6K drops fuel level quicker than when a load is on motor.
Recovery from tank flow comes quicker than the revs drop from a free-unloaded rev of the motor.
A somewhat more gradual rev, the fuel levels stay constant......just an FYI.

I have a suspicion that the slide/metering rod want to come play before they are invited.

[BA80]

Here's some breakfast puddin' for you moto. Look at the down pipes on my bike. all of them are a nice gold color EXCEPT #4, it's purple. This happened over about a year on a brand new Mac system and probably 20 -30K miles. When I noticed it was running leaner than the others I pulled the carbs and found that the float level was slightly lower in that carb than the other 3. I repaired the problem.

[motoman]

Had similar issue several yrs. back BA80. Of course the stock double wall header pipes didn't show any indication of a lean issue, the plugs had a hint of Greg look to them. This was after I got bike back, had swapped motors(same 81 4R1 motor). Just transferred the carb bank to it as it seemed to be working fine.....no re-sync or internal inspection. Rode that way for a couple yrs., but always seemed a little 'soft'. That's when I found, not only had the carb bank been changed to a Special carb bank, but also had 105mains, which is two steps lean from stock! Unknowingly at that time, the correct 110 size were K&L not Mikuni. Corrected that and found the 185 air jets were also K&L's. Corrected that and its been a slippery slope downhill ever since having to correct low voltage issues, pickup wires, etc.......you know the drill. So that's a little background.......and yea, J.W. would be somewhat correct commenting some time back that I must have the patience of Jobs. I would better describe it as having another turn-key, trouble free LD bike........but at least I'm persistant........slow getting on task, but persistent once there.

[motoman]

Had similar issue several yrs. back BA80. Of course the stock double wall header pipes didn't show any indication of a lean issue, the plugs had a hint of Greg look to them. This was after I got bike back, had swapped motors(same 81 4R1 motor). Just transferred the carb bank to it as it seemed to be working fine.....no re-sync or internal inspection. Rode that way for a couple yrs., but always seemed a little 'soft'. That's when I found, not only had the carb bank been changed to a Special carb bank, but also had 105mains, which is two steps lean from stock! Unknowingly at that time, the correct 110 size were K&L not Mikuni. Corrected that and found the 185 air jets were also K&L's. Corrected that and its been a slippery slope downhill ever since having to correct low voltage issues, pickup wires, etc.......you know the drill. So that's a little background.......and yea, J.W. would be somewhat correct commenting some time back that I must have the patience of Jobs. I would better describe it as having another turn-key, trouble free LD bike........but at least I'm persistant........slow getting on task, but persistent once there.

Greg was supossed to 'grey'........was a 'Droid' thing, and am not very compatible with it.......need to stick with the laptop.

[TopCatGr58]

Greg was supossed to 'grey'........was a 'Droid' thing, and am not very compatible with it.......need to stick with the laptop.

Hey Brant, Greg IS Grey, so they are interchangeable!!

T.C.

[BA80]

shazbot! nanu nanu

[Bonz]

I have had my screws at 1.75-2.25 out from lightly seated from the day I rebuilt the carbs in 2010. I had them at 1.75 for the Rally this year knowing it was gonna be hot, we were doing Pikes Peak and other riding that would take the bike from 6000 feet in canon city, to 9000 feet at Bishops castle, to 14,110 feet on the top of Pikes Peak. Bike ran great the whole time, even on top of pikes peak, albeit low on power breathing that rarified air! Even had nice tan plugs on top of Pikes Peak, ask CZ and 3Phase... Averaged 43 mpg for the rally.

Now, I have opened them up to 2.25 turns as fall is approaching and cooler temps are here in the morning and evening when I ride the XS. ZRX is my daily driver.

I know what works on carbs, none of it is my original thinking, it is based on all those that know a lot more than I do who have gone before. There is a lot of "if, but, when, only if the moon is full" stuff floating around that is nothing but a dead end when it comes to carb tuning.

This link below is GOLDEN for anyone who wants the step by step process to get carbs done right. Helped me keep on task and not go re-inventing crap when putting the ZZR1200 carbs on my ZRX1200.

All of it applies to our XS, and gets the proper parts selected in the proper order so that no matter what your locale or elevation, you get it right.

http://www.factorypro.com/tech/tech_tuning_procedures/tuning_carbtune,CV,high_rpm_engines.html

Now for some scotch!