Anatomy of the Carbs

[motoman]

May wanna re-read BOTH scenarios.........definitely a comprehension problem exists......or as Bob's tag line says...."what we have here is a failure to communicate" .

[BA80]

Let me see if I have this straight....less fuel in the carbs will make a bike engine run rich........diesel engines can run to the point of scattering on NOTHING BUT AIR.

All is well in Bizarro world.

Ok Brant, you be right in your world and I'll stay right here in reality.

[motoman]

NOTHING will run on straigt air or the oil companies would be out of business. It had to be getting a lot of fuel somehow. A diesel has no throttle plate on the intake.

How does an example of an engine needing BOTH air and fuel to run become irrelevent?

Well Greg, just cause you have never heard of it happening doesn't mean it didn't . There is a technical name for that phenonima, but can't remember it. Guarantee there was no fuel involved! Problem was, there wasn't a bed sheet sized rag in the shop big enough to toss in that 5" intake snorkel.
That was part of reason for stating the irrevelency of your reasoning........and yes, if cyl. Temps are hot enough....add in the extreme heat created from compression only of the molecules, a diesel cyl.WILL go BANG for several cycles till that phenonima drops cyl. Temps.......see.....not a wasted day......ya learnt' sumptin'.
The irrelevancy was partially referring to that.
The rest of the irrelevancy is your trying to side-track what I already know to be true from hands on experimentation.......some which I admit was accidental findings, but with further testing, verified to be true. Now if you had done the same, you would 'have a leg to stand on'.
Don't forget what I've said on the board in the past.......I don't suggest anything that I haven't already found to be true. May get a bit confused with my own wording, but I challenge to find a single thread where I've totally misled anyone .........Besides, I'm STILL having' way too much fun .

[BA80]

Hmmmm........maybe convert the dern thing to diesel technology.........but, then again, ever literally seen a diesel 'runaway' and gernade on straight air intake?......witnessed a 350 Cummalong do it ONCE...........scarey chit .

That makes your reference irrelavent in itself......just sayin' BA......

NOTHING will run on straigt air or the oil companies would be out of business. It had to be getting a lot of fuel somehow. A diesel has no throttle plate on the intake.

How does an example of an engine needing BOTH air and fuel to run become irrelevent?

[mack]

Tc

This is what I'd hoped for!

[motoman]

Hmmmm........maybe convert the dern thing to diesel technology.........but, then again, ever literally seen a diesel 'runaway' and gernade on straight air intake?......witnessed a 350 Cummalong do it ONCE...........scarey chit .

That makes your reference irrelavent in itself......just sayin' BA......

[BA80]

I understand how you might think that but in order to CREATE venturi velocity RPMS must increase which requires fuel. No fuel no RPM increase.

Exactly how a diesel engine runs, there is no control of the airflow, the intake is wide open. Increasing the fuel to add to the air intake increases RPM and horse power.

Adding more air to an already lean engine isn't going to increase RPMS. It can't suck in any more fuel than is there and CREATE a rich condition.

[motoman]

Since the EARLY 70's buddy, both professionally and otherwise.

You can be right, I don't care. Physics don't change though and the further a liquid has to climb the more work it takes to get it there. Get a long straw and test that fact.

Exactly right BA80!......now follow this: since it takes more throttle plate opening(greater venturi velocity) to pull that fuel up with the lower fuel level, you now have a manifold DROP in vacuum causing the spring in the diaphragm assembly to overcome that vacuum drop raising the main circuit metering rod higher than what SHOULD be normal for that particular load demand.......wa-la......more fuel .
While on the subject, pertaining to FUEL idle mixture screws, a little known 'secret' to more easily and more PRECISELY to detect that EXACT point of engine and exhaust sound setting idle mixtures using the more accurate 'lean-drop' method, is to first polish the tapered ends of those mixture screws with a small piece of super fine Emory paper or crocuses cloth. Decades ago, in the automotive world I found doing this allows a perfectly smooth flow of the fuel going past that metered point. It also gives an EXACT location of the near perfect mixture combination of a pilot/idle circuit.

That correct ' lean drop' drop method in the automotive world is with mixture screw's backed substantially beyond that point for starters........gradually coming back in till that ever so slight sound change.....then rotate back out 1 to 1 1/2 turns out......go to next one, do the dame. .

Now, in the cycle world with side draft/downdraft carbs, that final ' backed out' setting is 1/8 to NO MORE than a 1/4 turn.

The ' just when it reaches the highest in. vacuum point' does obviously work, but that also DOES leave the setting at a to rich a mixture.
You'll get away with that at your location and lower elevation, but approx. 4,000ft. and above(I'm @ 4,800ft. and every direction goes UP from there), and exhaust smell WILL reflect that . Hope that cleared up(no pun intended) up the tank ..........

[BA80]

Since the EARLY 70's buddy, both professionally and otherwise.

You can be right, I don't care. Physics don't change though and the further a liquid has to climb the more work it takes to get it there. Get a long straw and test that fact.

[motoman]

Marshy....all for teachin' an old dog new tricks, and that IS correct......to a certain extent......then 'real world' kicks in. Since my 40+ years of building and setting up carbs as a hobby and semi-professionally, on a daily bases counts for nothing, you do as you will

BA80....not as simple as that....nice if it were. To low a fuel level in bowl WILL cause a lean air/fuel mixture......at idle and slightly above. Beyond that, more than needed throttle plate opening is needed to create the same ' work load', and to overcome the straw effect, resulting in increased venturi velocity that WILL draw more volume of fuel than needed for the actual work load.......little more to it involved, but that's the jest to it. I have proved this out to be true in the automotive world, and find no difference with side draft/downdraft bike carbs. They all work on same principal. So, unless you've rebuild, setup and experimented with automotive carbs in the close to four digit numbers over four decades, disputing my suggestions related to that field is a moot point.

Could care less about the 'I'm right, your wrong' BS........but pickin' a couple folks here's brain pertaining specificly to the later BS34 carbs, combined with many decades on a REGULAR bases of carb rebuilding and setting up in the automotive world, not as 'line' mechanic where you rarely see vehicle sgain, think that qualifies as knowing a little something .

[WMarshy]

Guess you all have totally forgotten about venturi velocity resulting from an increased throttle plate opening, which would be needed to compensate for a lean cond in order for engine to produce the same needed 'work' level relative to if metering were working correctly.
Sorry if you guys ain't 'gettin' it, but no need to twist things around to fit your justification just cause your not following what Is actually taking place. This is not ALWAYS the case, but a too low a fuel level in ANY carb, whether it be automotive(downdraft), motorcycle side draft/downdraft, or an updraft on a damn old 8N Ford tractor, guarantee that's what can be the result of a too low a fuel level! On top of that, if its associated with a CV carb, then you have improper slide/metering rod positioning from incorrect throttle plate opening........problem just 'sno-balls' affecting rest of circuits needs.....incorrectly of course.

The only one that "aint gettin it" it is you. You should consider some light reading from a reputable source about float heights and its effect on stoichiometry.

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

[BA80]

Oh, I get it. Drop your float levels and see how rich it runs.

[motoman]

Guess you all have totally forgotten about venturi velocity resulting from an increased throttle plate opening, which would be needed to compensate for a lean cond in order for engine to produce the same needed 'work' level relative to if metering were working correctly.
Sorry if you guys ain't 'gettin' it, but no need to twist things around to fit your justification just cause your not following what Is actually taking place. This is not ALWAYS the case, but a too low a fuel level in ANY carb, whether it be automotive(downdraft), motorcycle side draft/downdraft, or an updraft on a damn old 8N Ford tractor, guarantee that's what can be the result of a too low a fuel level! On top of that, if its associated with a CV carb, then you have improper slide/metering rod positioning from incorrect throttle plate opening........problem just 'sno-balls' affecting rest of circuits needs.....incorrectly of course.

[WMarshy]

Using this as a visual aid, and knowing that our carbs use vacuum to draw fuel up to the carb throat, you can easily see that if your fuel height is too low then it would run lean because it's 'harder' for the carb to draw up the fuel. Conversly, if the fuel level is too high, then too much fuel would get sucked up and it would be too rich..

That's EXACTLY what I said and EXACLY the opposite of what you said. Can't find the quote right now.

OK, found it. Rereading it I can see what your theory is but actually if you think about it less fuel can't make more fuel.

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.

I agree with Greg. I also tried to offer some insite about fuel level and burn mixtures in another thread... Plain and simple, low fuel level in carb = lean condition and high level = rich condition. There is no mechanism/function in the carb that will compensate for a low level and make it into a rich condition. Silly talk.

[BA80]

Using this as a visual aid, and knowing that our carbs use vacuum to draw fuel up to the carb throat, you can easily see that if your fuel height is too low then it would run lean because it's 'harder' for the carb to draw up the fuel. Conversly, if the fuel level is too high, then too much fuel would get sucked up and it would be too rich.

That's EXACTLY what I said and EXACLY the opposite of what you said. Can't find the quote right now.

OK, found it. Rereading it I can see what your theory is but actually if you think about it less fuel can't make more fuel.

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.