rotarydoc

what size of webber carb do i need on a 12a non-ported and a street ported motor? the carb will be a down draft style.

Fool Boost

A 48IDA will work great. I found 40-42mm venturies work well on an extend port.

rotarydoc

thanks man for the info. i'll be picking up my 3rd fb (1st gen) on next friday. the car is imaculant on the inside and runs great. the car is a one owner car, i'll be the second. i'll post pics when i can.

Aussieninja

Hi there sorry to hikack the post, but I am having a devil of the time tring to tune my 48IDA on my large extend port.



simply connot get my idiling circuit and progression to main working properly.



This is my set up and the car is running like a two legged dog.

Main jet:200

Air correction jet 160 F11

Pump Jet 45

Idle jet 65

Idle jet holder 120



The car will not cruise at low revs and it starts going crazy at 2200RPM. What i mean is that it satrts bucking, coughing and missing.

If I put my food down, no problems. It will simply not work at low revs and low speed. So what gives?



I have replace all ignition with new and definately not ignition issue.

Can any one help?



Cheers

nakedchicken

PM wackyracer @rx7club.com. He helped me in the past.

moremazda

#1 verify that you have proper fuel pressure. It needs to be 2.5-3 psi.



#2 verify that the float is set to the proper hight. It should be 5.5-6 mm above the casting. Weber sells specific tools for this.



Now these are for the IDA. Are you sure that you have an IDA and not the IDF. I ask because you are listing an idle jet that works for the IDA. The IDF the same idle jets as the DCOE which are listed as "##F#". They are the idle fuel and idle air in one jet.



Ryan

Lynn E. Hanover

I don't tune in this area (RPM) but here are a few thoughts:



A 200 fuel jet is huge. Unless your choke size (venturi) is over 38MM.



A 44MM choke will support 300 HP. A 36MM choke will support 245 HP. You won't get close to this so stay at or below 36MM for choke size. The car will be much more responsive and far easier to tune.



For 36MM 160 mains and 160 airs is a great all around starting point. The problem you see can have many causes. One is float level too high. Where the engine stumbles and shakes the carb a bit and it goes over rich for a second. If that wets a plug and it shakes again, you can see where it goes from there.



The stock needle and seat will not take much pressure, so a 3 pound max is good. We use a gross jet and 6 pounds in a highly modified carb.



Remove and discard the screen that sits on top of the needle seat. They plug up and become the main jet.

No matter what you have in there, that screen controls all flow.



The main jet controls all flow into the jetting circuits. So a bigger main jet changes all other jetting.

The air correctors at the top of the emultion tubes control high speed mixture. Bigger jet + leaner, and smaller jet + richer.



the transition from off idle through the RPM where the choke size and air corrector has control of mixture is where the tuning goes to hell. One tool is the accellerator pump spray nozzles. Bigger gives a short duration rich squirt. Smaller gives a longer duration leaner squirt. This can help cover a poor transition mixture.



The bigger the choke size, the longer the transition period, and therefore the better the transition tuning has to be to keep it from falling on its face right off idle. (after the pump jet quits).



In all out racing there is only one area where the low end counts for anything. On a long spool down, from top RPM, like the end of a long straight, we have a way over rich idle jetting, to make really cool fire ***** and big bangs that the crowd loves. Actually it keeps the apex seals lubricated at high RPM, because we premix the oil.



We also run MSD- 6ALs on both leading and trailing, and that covers up just about any poor tuning.

We look for 1575 to 1600 degrees of EGT right though the HP range (7,800 RPM to 9,600 RPM) for best power. About 248 HP from 38MM chokes.



When you get it going real good through the mid range an it goes lean at the top, (after a few seconds at the top RPM) you want to open it up and carve a notch at the top of the unused pump well. Drill a 1/4" hole at the very bottom of the well. This will add bowl volume and let it carry your top end mixture for a second or so longer. Don't give up. The very best cars ever built use that carb.





Lynn E. Hanover

fcrotornut

Sorry to hijack an allready hijacked thread, but its not often that you see detailed descriptions like lynn's.



so a question for you lynn, i have a holley 600 that ran great for awhile there, until i went to install a heat shield, i broke the ear off the base plate and could only fidn a baseplate for a holley 650.



it was all machined properly to match up with the one sent by racing beat, i even bored out the bottom of the carb to match up with the eight of an inch difference with the baseplate.



however i did not match the manifold port size.



i hooked it up again and it ran really shaky for about 2 days, would hold a rough rought shaky idle at 1.2k



i went out for a nice drive in the cold winter air for a night, parked it, went out hte next morning to get to work, cranked it over, it shaked and stuttered through every rpm while cranking qnd would not hold an idle unless i held my foot on the accelerator, and after a few moments of that, it would drop idle and stall with my foot still holding the accelrator down.

walkingwallet

Hi Y'all,



First post so please advise if I'm not following proper guidelines.



I have a mid engine sandrail with a early 13B motor, street ported, and just put a 48IDA and manifold on the car this holiday weekend. After some preliminary research I started with F11 emulsion tubes, 150 main jets, 120 air correction, 37mm chokes, 55F10 idle jets. Have a low pressure high volume electric fuel pump from Carter (green).



The install went great. Fired right up, idled fantastic. Initially, during warmup, had no hesitation or bog thru the progression circuit and screamed at mid-high rpm. During the first test ride, after warmup, it developed a hesitation off idle, but slight feathering of the throttle overcomes the transition problem. Certainly not desireable but I was able to ride with my hombres thru the desert.



I had no other idle jets to experiment and the car is in mexico where we ride in the desert/dunes. No auto parts stores with this type of part available. My research of printed materials leads me to believe that I should take a size larger and smaller idle jets with me and try them. I'll install a fuel pressure guage and regulator and set it to 2.5lbs before I start making any changes, after reading the above threads.



I don't have any of the other carb specifications available currently but I'll take some notes next visit to mexico.



Any suggestions are appreciated. I typically read and then throw money at the problem. Works sometimes.



This car has had a slightly modified factory carb and worked great until a leak in the roof rusted the throttle plate. But it NEVER ran like it did this weekend. I'm used to being the fastest in the crowd with the 13B but this setup kicks serious butt.



Robin

Nick16

umm ask carl at rotaryshack.com



hes got weber carbs on his site.



hes got a 45 weber also.







maybe somone needs to make this into a new topic