Kim's FB

Ok so I thought my issue with the bog at WOT was caused by my current ignition set up. When I floor it it bogs unless I gradually and slowly press the accelerator pedal. I changed some recommended jets, and put the ignition back to stock for testing. The bog is still there. I have 3 books on Weber carbs, that I read, and I reaserch on line, but everything else is all related to piston engines and it keeps confusing me. I've never worked on carbs and so this is all new to me. Here is my current carb and set up:

50mm dco carb
46mm venturies
180 fuel jets
160 air jets
0 bypass accelerator pump jet Changed to 55 accelerator jets
f7 emulsion tubes
65f8 idle jets Changed to 65f9
300 needle valve


On my reasearch I came across this article:

The typical symptom on a book-value Weber conversion is a bog unless you baby the throttle. (That is exactly what is happening with my Weber) This is because the mixture leans out when you try to suddenly involve the main jets with insufficient airflow. When you bring airflow up more gently, the progression circuit helps you out, and the air is moving faster when you get to demanding fuel from the main jets.

This shows that fuel volume is insufficent for fast throttle movement. We increase accelerator pump volume / unit time most easily by enlarging the metering hole (this item is as easily accessible as the main and idle jets). Use a pin vise and a set of drills 61-80 to gradually enlarge the metering hole.


Could that be the cause of my problem? I set the step mixture and it starts up good, and idles perfect, but I do get an eratic high/low idle when coming to a stop after driving. It does however guzzle gas like a motherefer.

Keep in mind that i'm running a supercharger with a stock port 12a, 3/8 fuel lines with 3/8 return on a msd fuel pump with a mallory boost referenced regulator.

I hope you guys can help me out.

Thanks,
Kim.

Hades12

I have no ideal how to help you but here is another book on tuning.

http://www.matthewnanney.com/images/Carb/

FIBREMAZ

It may seem expensive in the start but an EFI system will pay the difference off via using a lot less gas to make the same power. I have an injected PP motor and bog/lag is almost nonexistant. Expect to use up to twice as much gas for the same journey with a weber as you would with EFI.

j9fd3s

iTrader: (3)

is it bogging when you're moving the pedal? or is it bogging after you're done moving your foot?

the accelerator pump compensates for the opening of the throttle (air is lighter than fuel...), so if it bogs during or a little after you open the throttle its an accel pump.

if you hold the pedal steady, and it still does it its a jet/emulsion tube issue.

13 beef is right, efi would help a lot, especially with the supercharger

Latin270

Nah, I think that would be a PITA to fuel inject a 12a, especially since an upgrade $$$ card is already in the picture.

candyassmiler

a local tuner told me many times they have to drill out the metering hole to get rid of the flat spot on his drag cars. that very well could be your problem.

Siraniko

iTrader: (13)

Start with smaller venturies say 38 then work your way up.

REVHED

I seem to recall suggesting it's probably the carb last time but got shot down.

You'll never be able to just stamp on the throttle and expect it not to bog especially with large venturis like that. You need to gently feed it in. Try going to a smaller venturi.

REVHED

Why would it be a pain? All you have to do is swap the carb for the matching Weber style throttle body. Bolts right in. The fuel system and ECU is a breeze if you know what you're doing.

Kim's FB

I know, I know. Happy you can still help me

I am considering fuel injection. Eventually that is what I will be doing. But now I have to deal with this carb. Yeah, Robert told me to go smaller, I ordered some smaller venturies that have not arrived yet. I will try those once they get here.

So I shouldn't bother with the metering holes? and just play with venturi sizes?

Kim's FB

The TWM tb 2900 series is what I will be getting once I save some $$ It will fit nice with my side draft manifold. I could deal with map sensors, injectors and the wiring and such. Tuning the standalone is what's going to be challenging for me.

Hell I already have the fuel tank, lines, pump and regulator. The price on the tb is not bad at all, but not including the injectors, rails, tps, and map sensors. If I could find a nice set up for under a grand I should be ok. How much can standalone systems cost?

FIBREMAZ

You could also try some different emulsion tubes

blwfly

iTrader: (4)

lol that paragaraph pretty much tells ya what to do start small and go up

by the end you can be our weber guru/shop

680RWHP12A

exactly, wacky, good call

Kim's FB

I don't think there are 38mm main venturies for my 50 dco. I could be wrong, but the lowest I think I can go is 40mm with my 50 dco
Robert, can you check that out for me?

So as a starting point (assuming I did use 38mm venturies) a formula to calculate my starting main jets is to multiply venturi size by 4. So I need to start with 150-155 main jets. And as a general rule I should go around 50 higher on the air correctors, so around 200 for the air jets.

For idle jets it is recommended I use 60 idle jets for my 573cc per rotor 12a. That I need to research more.

f7 emulsion tubes I think can stay the way they are according to my research. f2's maybe. As I understand it, the sizes (lean to rich) can determine how fast or slow the main circuit starts. I think this is playing a key role in my problems now, but all that will change after I change the venturi size.

So I will go lower on the venturi, lower on the main jet, higher on the air jet, and maybe lower on the idle jet. HUH?

Kim's FB

Thanks for that book. I have it, but it will be nice to have it on my computer.
I also have and reading Pat Bradens book, and the Haynes Weber manual.

These carbs are relativelly easy. There's really nothing to them. Understanding what each circuit does and how they perform is the key. Once I figure that out (getting there) I will be a guru LOL. I really do want to learn more, but the more I learn the more I should be looking into efi for my set up. That will come eventually, but for now i'm not giving up on my Weber. We are becoming good friends. I might even write a book. "A girl and her Weber" Until then, I'll just keep reading and take up advice from you guys, and pick my toes:

Hades12

I also enjoy picking my toes.

blwfly

iTrader: (4)

hahaha
have you ever had drunk people walk into your wall


ohh and there is a thing called nail clippers or if you cant offerd one cause of the webber use sisors

oh by the way thats one trippy couch

Kim's FB

Everyone loves to pick their toes. lol.

Nail clippers? Nahh, us females get pedicures. Men use toe nail clippers. Guys who don't know me or seen me tend to think i'm butch cause I work on my car. But i'm a gilrie girl, I just love to work on my car.
No one drunk has ran into it, but I do get wow you painted that and I follow with "It's wall paper jackass". Hahaha damn drunks!

Me with family in Washington.

Rogue_Wulff

It's almost amazing to me, because you look very similar to my daughter, who also likes to work on cars........
I guess I raised her right.

blwfly

iTrader: (4)

it takes intellegence to work on cars not butchness
if they think your butch well there just plain old jelouies since they dont have what it takes and fork out$$$

my defintion of butch is a 6ft female who looks almost manly is 300 pounds can lift 200pounds and has a army hair cut,also a rug muncher lol

bye the way im sure every guy wants to meet ya iv never knowin of girl into cars like you
i consider it special

Hyper4mance2k

iTrader: (40)

smaller chokes is my next guess. And in a rotary you want smaller air bleeds than main fuel jets.

REVHED

Same here. I get a slap from the girlfriend every time she sees me doing it though.

Hyper4mance2k

iTrader: (40)

Kim I don't know if you saw my alert on weber jets.

https://www.rx7club.com/showthread.p...ht=weber+alert