 Re: Lighter Carb Springs
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Joined: Jul 2008
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Learned Hand
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Learned Hand
Joined: Jul 2008
Posts: 1,440 |
Quote:
The only place this should even be a concern is on low speed transition, in which case the elevated slide/needle theoretically caused by a too-light spring could induce a transient rich condition.
I don't see how it could ever go rich. Fuel is pulled into the airstream by the venturi effect. It always lags behind throttle opening. This is one of the reasons some carbs have accelerator pumps.
'08 America Blue/White; Custom Headlamps, Custom Lowers, Clearview 20", Bafflectomy
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Re: Lighter Carb Springs
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Joined: Feb 2008
Posts: 2,671 Likes: 15
Loquacious
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Loquacious
Joined: Feb 2008
Posts: 2,671 Likes: 15 |
Quote:
...I don't see how it could ever go rich...
The same way one can bog a flatslide (or other direct connect slide) by opening it too fast & inducing a temporary transient rich condition. And I've done that first hand. Anyone with substantial flatslide experience can tell you that's a real condition under certain circumstances. That said, this mostly theory anyhow on the CV carbs.
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Re: Lighter Carb Springs
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Joined: Jul 2008
Posts: 1,440
Learned Hand
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Learned Hand
Joined: Jul 2008
Posts: 1,440 |
Quote:
Quote:
...I don't see how it could ever go rich...
The same way one can bog a flatslide (or other direct connect slide) by opening it too fast ... That said, this mostly theory anyhow on the CV carbs.
Well, I didn't say that it wouldn't bog down. I just said it wouldn't be rich. The bog you get is from being temporarily lean. As for theory, the lighter the spring becomes, the less the carb will behave as a true CV.
'08 America Blue/White; Custom Headlamps, Custom Lowers, Clearview 20", Bafflectomy
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Re: Lighter Carb Springs
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Joined: Feb 2008
Posts: 2,671 Likes: 15
Loquacious
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Loquacious
Joined: Feb 2008
Posts: 2,671 Likes: 15 |
Quote:
...Well, I didn't say that it wouldn't bog down. I just said it wouldn't be rich. The bog you get is from being temporarily lean...
Bog = rich. We apparently disagree as to the cause.
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Re: Lighter Carb Springs
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Joined: Jul 2008
Posts: 1,440
Learned Hand
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Learned Hand
Joined: Jul 2008
Posts: 1,440 |
I don't mean this to sound condescending, but I think you've fallen prey to a common misconception. Can you explain in terms of carburetor airflow (and/or manifold air density) and metering why it would go rich? It has to be examined at that level in order to identify the cause. 
'08 America Blue/White; Custom Headlamps, Custom Lowers, Clearview 20", Bafflectomy
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Re: Lighter Carb Springs
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Joined: Feb 2008
Posts: 2,671 Likes: 15
Loquacious
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Loquacious
Joined: Feb 2008
Posts: 2,671 Likes: 15 |
Wow, those are fancy words. What happens to the needle when a CV slide lifts?
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Re: Lighter Carb Springs
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Joined: Jul 2008
Posts: 1,440
Learned Hand
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Learned Hand
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Quote:
Wow, those are fancy words. What happens to the needle when a CV slide lifts?
The needle moves in conjunction with the slide to increase both the fuel and air.
'08 America Blue/White; Custom Headlamps, Custom Lowers, Clearview 20", Bafflectomy
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Re: Lighter Carb Springs
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Joined: Sep 2007
Posts: 198 Likes: 1
Adjunct
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Adjunct
Joined: Sep 2007
Posts: 198 Likes: 1 |
When you wack the throttle open with slide carbs at low revs the bog down is lean, accelerator carbs stop this by pumping more fuel to stop the bog down.
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Re: Lighter Carb Springs
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Joined: Mar 2005
Posts: 57
Member
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Member
Joined: Mar 2005
Posts: 57 |
"When you wack the throttle open with slide carbs at low revs the bog down is lean, accelerator carbs stop this by pumping more fuel to stop the bog down."
That's correct.
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Re: Lighter Carb Springs
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Joined: Jun 2005
Posts: 534
Adjunct
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Adjunct
Joined: Jun 2005
Posts: 534 |
dyno jet springs are lighter i had a GPZ900R fitted K&N and dyno jet and it came with lighter springs and with a good pipe and set up it is noticbly quicker on pick up and go i think maybe the stock kwak springs might be just as heavy 
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Re: Lighter Carb Springs
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Joined: Jul 2008
Posts: 1,440
Learned Hand
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Learned Hand
Joined: Jul 2008
Posts: 1,440 |
Quote:
Quote:
"When you wack the throttle open with slide carbs at low revs the bog down is lean, accelerator carbs stop this by pumping more fuel to stop the bog down."
That's correct.
That's what I said earlier, several comments up the thread. Now, can you give two reasons why the intake charge goes temporarily lean (I provided one of them already)? Yep, it's a test!
'08 America Blue/White; Custom Headlamps, Custom Lowers, Clearview 20", Bafflectomy
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Re: Lighter Carb Springs
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Joined: Feb 2007
Posts: 23,217 Likes: 61
Fe Butt
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Fe Butt
Joined: Feb 2007
Posts: 23,217 Likes: 61 |
What I was talking about was NOT when you wack the throttle but when you are holding it steady at a given RPM when the main is in play around mid range. I also wasn't saying it is rich just wondered if that may be a side effect. Lower RPM slide and main open farther, don't know. As I said before I haven't messed with these vacuum operated slides before just cable operated.
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Re: Lighter Carb Springs
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Joined: Jul 2008
Posts: 1,440
Learned Hand
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Learned Hand
Joined: Jul 2008
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Quote:
What I was talking about was NOT when you wack the throttle but when you are holding it steady at a given RPM when the main is in play around mid range. I also wasn't saying it is rich just wondered if that may be a side effect. Lower RPM slide and main open farther, don't know. As I said before I haven't messed with these vacuum operated slides before just cable operated.
Right, we got somewhat sidetracked. However, you did say you thought the weak spring might cause a rich condition at midrange...
Quote:
because the slide and needle could be open at a slower RPM given that less vacuum is needed to open them thus supplying more A/F than required for that given RPM.
I think this implies the same misconception about mixture as the "bog" issue noted by the other poster. A/F is either correct or it isn't. If you get more of it, you accelerate. It doesn't make the motor rich. In terms of midrange, the motor might surge because the weak spring causes loss of throttle control. It doesn't surge because the early throttle opening has changed the mixture.
'08 America Blue/White; Custom Headlamps, Custom Lowers, Clearview 20", Bafflectomy
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Re: Lighter Carb Springs
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Joined: Feb 2008
Posts: 2,671 Likes: 15
Loquacious
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Loquacious
Joined: Feb 2008
Posts: 2,671 Likes: 15 |
I don't have the Kawi springs yet, but expect to have them in a few days.
Yes, flatsides have accelerator pumps. Whether a flatslide bogs because it is lean or rich is going to depend in part on the setting of the accelerator pump. That was in retrospect not the best example to use for the purpose of this discussion.
Our Keihin CV carbs don't have accelerator pumps.
The question from my perspective was, as I recall it, what influence slide spring rate has on the mixture properties of a CV carb. My theory was on a CV carb a lighter spring rate than stock could theoretically have a slight, temporary transient rich effect at low RPM's as a consequence of a bounced elevated needle, if the tension was insufficient for the vacuum for a given situation. As a practical matter provided the spring has sufficient tension I don't think that it will make any difference on the road, or on the dyno.
The question in my mind is what role, if any, does slide spring rate play with respect to CV carb air/fuel mixtures, presuming at least adequate spring pressure, whatever "adequate" is for a given carb setup?
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Re: Lighter Carb Springs
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Joined: Jul 2008
Posts: 1,440
Learned Hand
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Learned Hand
Joined: Jul 2008
Posts: 1,440 |
Quote:
The question in my mind is what role, if any, does slide spring rate play with respect to CV carb air/fuel mixtures, presuming at least adequate spring pressure, whatever "adequate" is for a given carb setup?
As long as carb operation is well into the main circuit, the spring should have no substantial effect on mixture. Opening more quickly than the manufacturer intended is no different than pulling the slide/needle up manually on a pair of non-CV carbs. The difference is at low RPM, where the spring limits the throttle to opening at a rate supported by the pilot and transition circuits. The spring allows the idle circuit to be designed leaner, and mains to come in later. The potential drawbacks to lightening the spring are disturbing the metering relationship at low RPM (which can create the low-speed bog) and the possibility of mid-throttle surging.
'08 America Blue/White; Custom Headlamps, Custom Lowers, Clearview 20", Bafflectomy
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