Carb tuning, larger accelerator pump nozzle?

-
Mattax said:
Can, but not always.

Exactly. And that's the main purpose of an air bleed.
View attachment 1715799571

Yes. We can learn a lot by observing as the physical relationships aren't always as we think they are.
Click to expand...


Tell that to Bewy. I can’t remember when it is that a bigger MAB doesn’t always start the mains quicker, but I believe it’s some weird situation. Like when a power valve can open at idle and make the engine rich. I haven’t yet found an example of a bigger MAB delaying the start of the mains.
 
Bewy said:
An O2 sensor doesn't defeat the laws of high school physics.....
What you said above in post 73 exactly contradicts what you said post 69.
Click to expand...


Did you read post 73? Let me say it again. In normal tuning cases a: bigger MAB will delay the start of the mains and make the fuel curve leaner at higher rpm and a smaller MAB will delay the start of the mains and make the fuel curve richer at higher rpm.
 
That's the trouble Rat you have said it again, & I am sick of reading your nonsense. What you say above is the exact opposite of what you said in post 65: decreasing the size of the MAB will delay the mains.
Have you got a 3rd version for us?
Then you add some nonsense in post 76 about 'a weird situation' when a power valve opening at idle causes a rich idle. Not weird at all if you understand how carb works....For this to happen the t/blades have to be open too far at idle, causing the main system to start.
 
Bewy said:
That's the trouble Rat you have said it again, & I am sick of reading your nonsense. What you say above is the exact opposite of what you said in post 65: decreasing the size of the MAB will delay the mains.
Have you got a 3rd version for us?
Then you add some nonsense in post 76 about 'a weird situation' when a power valve opening at idle causes a rich idle. Not weird at all if you understand how carb works....For this to happen the t/blades have to be open too far at idle, causing the main system to start.
Click to expand...


Yup, I’m going to have to block your dumb ***. I said it once and that should have been enough. I’ve typed it wrong several times because you are a book reading fool who evidently hasn’t tuned anything. One more time to clean it up because I have typed it wrong several times now. Here you go. In most cases:

Increasing the MAB will START the main circuit sooner and lean the fuel curve at higher rpm.

Decreasing the MAB will DELAY the main circuit starting and richen the fuel curve at higher rpm.

Do you get it now? That’s not what your books says, but there are way too many links around here that explain how this is. And not books by some guy who is out to make his money selling stuff to street/strip guys. NACA 49 comes to mind.
 
Here’s a post by some guy that used to post here regarding what’s being ping ponged here:
4595A3A2-AF13-486A-9BB7-179959E3758A.png
 
Rat,
So now the story changes AGAIN between post 77 & 80. And your calling me a dumb ***.....
And as far as 'haven't tuned anything' , I was fitting twin 35 mm Dellortos to my Knuckle Head Harley in 1967. Probably before you were born.
You don't know what you are taking about; typical of those with little actual knowledge, start name calling when they get caught out because that is the best they have got...
 
Bewy said:
Rat,
So now the story changes AGAIN between post 77 & 80. And your calling me a dumb ***.....
And as far as 'haven't tuned anything' , I was fitting twin 35 mm Dellortos to my Knuckle Head Harley in 1967. Probably before you were born.
You don't know what you are taking about; typical of those with little actual knowledge, start name calling when they get caught out because that is the best they have got...
Click to expand...



Yep, because you are such a pip, I’ll say it again. A bigger MAB will start the mains sooner in most cases and make the fuel curve leaner at higher rpm. It’s not that hard, but all the nonsense you vomit out caused me to get my thoughts out of order. I’ve corrected it several times just for you because you are so special. A bigger MAB will start the mains sooner. Did you get that yet??? When quoting Ulrich, don’t forget he is another one of many authors who tell people to use the wrong power valve because either they don’t understand how it works or they don’t care. It’s the same thing with the MAB and you just don’t get it. A bigger MAB will start the mains sooner and lean the fuel curve at higher rpm. A smaller MAB will delay the start of the mains and make the fuel curve richer at rpm. Did you get it yet? Has my redundancy helped your comprehension. A bigger MAB will start the mains sooner. There you go.
 
Rat,
So now it's my fault that you are spewing out all this nonsense???????? Chopping & changing on what affect the AB size has on when a cct starts.
Might be time to change the breakfast cereal.....
For your carburetor education, try Walter Larew's book Carburetors & Carburetion, ISBN-0-8019-5224-7. 164 pages.
 
Actually IIRC the graph that illustrates thie relationship best is in Obert.
Very funny Geoff that you have now come around to espousing those old books by automotive engineers that you previously dissed as outdated.

Got to say this whole dead thread revival has been entertaining. Dano got his carb figured out months ago and 12many got his question answered a page back. One of the things that was understood in the era of carburation was the importance of introducing the air correctly. That's really what we covered in this thread.
 
Bewy said:
Rat,
So now it's my fault that you are spewing out all this nonsense???????? Chopping & changing on what affect the AB size has on when a cct starts.
Might be time to change the breakfast cereal.....
For your carburetor education, try Walter Larew's book Carburetors & Carburetion, ISBN-0-8019-5224-7. 164 pages.
Click to expand...


I have the book. And I actually read it.
 
Mattax,
I never said any carb book was outdated. Show the post where I said that? In post #15, I commended info provide by engineers long ago.....
 
I’ve had a bit of time to actually sit down and think about the MAB and what it does. The only time I can think of when the MAB won’t start the mains earlier is if yo have a huge kill bleed or some other issue like that. Why you would have a big kill bleed I can’t say. But it would be one reason. The reason the MAB initiates the mains starting earlier is the pressure difference between the MAB and the fuel nozzle. That all by itself makes the mains start quicker. With the added air of the bigger MAB, you also change the viscosity of the fuel in the main well. You make the fuel less viscous with more air. A less viscous fuel/air mixture moves easier, so that initiates fuel flow sooner. It’s as simple as that. Anything else is attributable bad tuning decisions elsewhere in the carb.
 
Rat,
I think we are close to being in agreement. The size of the AB controls the start of the cct, as discussed earlier in the thread. Once the cct is started, the size of the AB, number, position & size of emulsion bleeds controls the amount of mixed fuel & air that gets delivered from the booster.
You have to have some sort of AB in the cct, otherwise the fuel will be syphoned from the booster until it empties the fuel bowl.
 
You must log in or register to reply here.
-

Back
Top