CV44 TUNING

[Sonny S.]

________________________________

just sayin   

[Jeffd]

so would shortening the rod on the acc pump help?

[Sonny S.]

that would delay the squirt as well as decrease it....could help

[FLTRI]

How 'bout a reason the AFR graph has such a wide variance in AFR: From about 11.7:1@2200rpm, up to 14.2:1@2700rpm, down to 12.5:1@3200rpm, and back up to 13.8:1@4500-up?
What can cause this swing in AFR?
Hint #1: It is not the accelerator pump.....except for a maybe a bit of richness @ 2200rpm, but the pump's influence is gone after about 1 second, or less, into the run so the rest of the AFR graph is devoid of influence from the accelerator pump.
Hint #2: It may be more than one issue causing the variance.
Disclaimer: This is assuming there are no issues/problems with the basics like AFR pumps not serviced properly, no air leaks in the exhaust system, or anything else that can corrupt the AFR readings.
Bob

[Don D]

BTW if you try to tune the Accel pump you can change the bypass hole as well for additional fine tuning

[mayor]

well I'll take a stab at Bob's questions:

How 'bout a reason the AFR graph has such a wide variance in AFR:

From about 11.7:1@2200rpm- pilot possibly set too rich, since this would be the split second the throttle was wacked before full load was registered

up to 14.2:1@2700rpm- load was applied and main jet was called to duty, but the acc pump gas had been sucked into the chamber yet

down to 12.5:1@3200rpm- accelerator pump squirted compensating for rapid gas need (although, over compensated is my official answer)

..and back up to 13.8:1@4500-up?- main jet was the source for gas needs.

What can cause this swing in AFR?
Hint #1: It is not the accelerator pump.....except for a maybe a bit of richness @ 2200rpm, but the pump's influence is gone after about 1 second, or less, into the run so the rest of the AFR graph is devoid of influence from the accelerator pump.
Hint #2: It may be more than one issue causing the variance.
Disclaimer: This is assuming there are no issues/problems with the basics like AFR pumps not serviced properly, no air leaks in the exhaust system, or anything else that can corrupt the AFR readings.
Bob

here would be my list of possible answers:

1. exhaust reversion (pipes or valves)
2. cam over lap (I/E)
3. cam timing (cylinder fill/cylinder empty issues)
4. exhaust pipe system compatibility
5. ignition timing
6. cylinder head flow velocity
7. constraints to fresh air (ac)
8. emulsion tube design
9. not enough tuning circuits in the CV44 carb
10. afr sampling rate
11. afr calibration
12. afr gremlins
13. AMC Gremlin


or combinations there of...

.....but in reality, a carburetor is a great compromise in supply of gas to an engine.   


how'd I do?

[FLTRI]

well I'll take a stab at Bob's questions:

How 'bout a reason the AFR graph has such a wide variance in AFR:

From about 11.7:1@2200rpm- pilot possibly set too rich, since this would be the split second the throttle was wacked before full load was registered

Pilot jet will not affect WOT...even for a split second.

up to 14.2:1@2700rpm- load was applied and main jet was called to duty, but the acc pump gas had been sucked into the chamber yet

Definitely the main jet was called to duty, but lack of velocity would be my guess as to the lean reading.

down to 12.5:1@3200rpm- accelerator pump squirted compensating for rapid gas need (although, over compensated is my official answer)

The accelerator pump was finished well before the rpms got to 3200.

..and back up to 13.8:1@4500-up?- main jet was the source for gas needs.

Fuel @ 4500-up is controlled by the main jet. Note: Usually the front and rear cylinder run different AFRs so it depends what cylinder the reading was taken. Ie: if the front cylinder was what produced the reading the rear cylinder could be leaner or richer than the front cylinder. Based on the this the main jet could be as good a compromise as possible or the "other" cylinder may be too lean or on the richer-than-necessary side.
This is why we always sample both cylinders on carbed bikes. This way we know where the jetting compromise needs to be.

here would be my list of possible answers:

1. exhaust reversion (pipes or valves) - BINGO!
2. cam over lap (I/E) - BINGO!
3. cam timing (cylinder fill/cylinder empty issues) YEP!
4. exhaust pipe system compatibility - YOU BETCHA!
5. ignition timing - Not so much
6. cylinder head flow velocity - ALSO POSSIBLE!
7. constraints to fresh air (ac) - Huh?
8. emulsion tube design - Possible, but not as likely
9. not enough tuning circuits in the CV44 carb - Also possible but not likely
10. afr sampling rate - Not unless there is a problem with the system
11. afr calibration - Probably not
or combinations there of...
.....but in reality, a carburetor is a great compromise in supply of gas to an engine. - TRUE!
how'd I do? [/quote]
You done good Mayor.  
Basically the exhaust system design and/or cam profile is what will shape the fuel curve. The rest of the variables can and do influence the curve but exhaust/cam that makes up most of the curve's personality.
Bob

[Jeffd]

so acc pump not much of an impact but how about the slide going up too fast due to too light of spring or too big of vaccum hole.  too much air pulling too much fuel?  ok I will go sit down and shut up know..

[FLTRI]

so acc pump not much of an impact but how about the slide going up too fast due to too light of spring or too big of vaccum hole.  too much air pulling too much fuel?  ok I will go sit down and shut up know..

If the slide is pulled too soon it will go a bit lean, then the velocity picks up and draws more fuel. So there can be a bit of confusion for the slide if the vacuum hole is too big.
For the most part if the vacuum hole hasn't been "hogged out" or the spring changed to too light tension, the velocity stays relatively high as the slide moves up and consequently draws more fuel through the main jet keeping the fuel/air balance on target.
It is only from screwing up that balance does the AFR get messed with.
The proof of that is readily seen with a bone stock bike. The AFR will be very flat. Then open up the hole in the slide too much and/or lessen the spring tension (Dynojet type kits) and the AFR curve no longer stays flat.
As always, JMHO,
Bob

[mayor]

The accelerator pump was finished well before the rpms got to 3200.

I'm not sure I completely buy that.  Take a look at the following afr example:


The Red, Green, and Blue lines are from different bikes using different cams and different exhausts configurations, and the only thing in common they have is they are equipped with the CV44 carb.  

Blue is from a TW54 ported heads (1.9"v) build using CS M-pipes 210main

Green is from a Crane300 ported heads(1.9"v) build using a D&D 2 into1 200main

Red is from a TW37 ported heads (1.805"V) build using factory head pipes and CS mufflers 200main

So, you saying that dip isn't related to the accelerator pump?

[Admiral Akbar]

So, you saying that dip isn't related to the accelerator pump?

It's not.. You need to drill an 0.040 hole at the top of the emulsion tube above the other holes.  Max

[FLTRI]

Gotta say Mayor I'm a bit perplexed. I know I shouldn't be because I see what cam profiles, accelerator pumps, exhaust systems, ports, big valves, small valves, exhaust systems of every design, do to fuel curves.
Here we have completely different builds, including cam profiles, porting, and different exhaust designs.....same fuel curve profile???
Got me

[mayor]

yea Bob, one more example of why efi is friendlier to tq curves.    

I like where Max is going with the emulsion tube holes, but I see that as a crap shoot on size and qty since it may require testing for each change to measure results. 

hey Max, rev limit on my tw37 build is set to 6.2k........take a gander at where the afr shuts off at.     se6.2 ignition, so could be noise or a problem created by one of those E.E. types.  I've got run files from 2 separate runs on that bike (3 pulls each), and each one carries the dropping tq line past 6.5k.  Another interesting note- the tw54 build stops at 5.8k (SE adjustable ignition set at 6k).

[Admiral Akbar]

so could be noise or a problem created by one of those E.E. types

Nope, Probably some idiot SW type... Max

[FLTRI]

yea Bob, one more example of why efi is friendlier to tq curves.

But we are talking about fuel curves not torque curves.
Try looking at those runs based on time in lieu of rpm.
Look at how the fuel curve goes as time passes. You should see the accelerator pump would have to go for a lot longer period of time to make the AFR go rich, that rich, for that long.
IME the way an engine breathes (cams, heads, intake, exhaust) dictates the fuel curve profile....not the carburetor...BWTFDIK
Bob

[Don D]

Wouldn't an AFR trace line flat as a pancake be fake on a carb bike?

[Sonny S.]

Jeffd has a flat AFR line with a CV .....don't know why but he does 

[mayor]

yea Bob, one more example of why efi is friendlier to tq curves.

But we are talking about fuel curves not torque curves.

...sorry, I was withholding evidence.  The tq curves follow the dips in afr on all three of those builds.   

it's funny, a fellow would think that the dips in afr would cause peaks in tq since 'ol Red is convinced that more gas is more power.  sorry couldn't resist busting on Red on a debate that's lasted almost two years.....although I think we might have him convinced otherwise now, since his recent afr was more towards our way of thinking

here's an afr/time comparison:

eventhough there's two Mississippi's between where the dip starts and ends, I can still see how the acc pump could be at the very least part of the problem.  The carb is working on vacuum, so if the vacuum momentum falls I can see how the affects could lag?  bwtfdik.    I agree that ususally the combination of components is what causes the afr signature in a carb build, but the signature is the same on the three vastly different builds that I posted the afr comparison for....so the one common denominator (cv44) probably bares some responsibility.  The more I think about it, I'm leaning towards the emulsion tube as Max mentioned. 

[Sonny S.]

>>>The more I think about it, I'm leaning towards the emulsion tube as Max mentioned<<<

why ?
then what ?
go ahead and drill it....lemmee know how it goes.

doesn't reds bike rev raster than both of yours?
and the 54 build revs faster than the 37 ?

[Admiral Akbar]

Hey Mayor, Thanks for the pic.. Max

[mayor]

doesn't reds bike rev raster than both of yours?
and the 54 build revs faster than the 37 ?

well, I'm not real sure how accurate the time function on the run files will show that, since some of that is subject to the fellow twisting the wick....but here's proof that my fxd can rev as fast to 5252 as red's roadcow:


I had to hunt for that run though, all three pulls of the lowrider seemed to reach that point over a half second slower. 


as for the other questions you asked......blame it on being a fellow who just has to tweak.     I won't drill the stock one, I'll order a back up first. 



no problem Max.....I have a feeling I may have given Red one of you as well.   

[FLTRI]

on a debate that's lasted almost two years.....although I think we might have him convinced otherwise now, since his recent afr was more towards our way of thinking

here's an afr/time comparison:

eventhough there's two Mississippi's between where the dip starts and ends...

So the throttle was opened and about a 1/2 sec later the AFR went a bit lean (>14.0). Speed of the thottle opening can affect this picture.
After 1 full second the pump's fuel just got to the combustion chamber and continued to squirt fuel into the carb throat for a couple Mississippi's???

Next time you have your a/f off check how long the accellerator pump squirts fuel into the carb.
Now imagine velocity helping to move the additional fuel through the process.
Do you still feel the pump is the culprit?
I think the carb can be tuned to help but not eliminate the basic builds breathing which dictates how and when the fuel is drawn through the carb.
As always, JMHO, Bob

[wfolarry]

Reminds me of the S&S dip that putting in an adjustable air bleed helps smooth out. S&S now puts them in from the factory so you can tune it.

[mayor]

After 1 full second the pump's fuel just got to the combustion chamber and continued to squirt fuel into the carb throat for a couple Mississippi's???

Next time you have your a/f off check how long the accellerator pump squirts fuel into the carb.
Now imagine velocity helping to move the additional fuel through the process.
Do you still feel the pump is the culprit?

well..  probably not so much....   I just need to practice how fast I can say Mississippi......

[PanHeadRed]

Mayor for what it's worth, here is the TQ curve and the AFR from my engine with the CV40 250 main and Caliber 2-1.

It could be drowning.

[attachment removed after 60 days by system]