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  #1 (permalink)  
Old 01-16-2009, 06:43 AM
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Cobra Make, Engine: E-M Cobra Ford FE 427 w/ Webers 48 IDA
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Default 48 IDA Interesting discovery

I am posting this to gather knowledge on the behavior of your 48 IDA and how it works in your application.

First, I would like to ask how well your motor is running. By this, I am simply asking are your plugs a tanish brown, and is your mixture 14.7 - 13.5 while driving and at idle.


I had very interesting conversation the past couple of days with a gentleman that had extensive knowledge with the 48 IDA (finally). Our conversation went in to great detail. As we were talking he pulled out a 48 IDA (cut in half) and explained from start to finish how the carb operates. He also explained the "Myth" as to why there is a certain type of camshaft spec for motors using the 48 IDA.

After explaining, he proved the "Myth" to be wrong. In his shop he fired up a motor that was in a RX 7 and show me the tach that was bouncing from 1600 - 2200 RPM (rotory) . Of course this was all out race car. After allowing the motor to warm up we took the car for a ride. I cant say that the idle was good but the mixture was good. Off of idle through the progression circuit and on to the main circuit the car drove flawless.

After heading back to the shop, we took another rx 7 for ride this one was more tamed but the drive from off idle to main was the same.


He explain to me that most people shoot in the dark when they tune these carb. By this I mean over riching circuit to solve the problem. He also mentioned its not that difficult.There are alot of variables involved.

Camshaft
rear gear
weight of car
altitude
transmission gearing
fuel pressure

With this being said, it is almost impossible to give someone a jet value and have them run it in their car and expect it to work. On the same token to troubleshoot a problem by hearing a person say I am having problems at a particular RPM.

You might be asking well why dont I just have him tune my car and solve the Weber problems for good.

Well, because I want to learn. Also if his practice is true I want to know how to so solve my problems in the future.

Note: By the way chokes are not needed in the 48 IDA if your looking for more volume of air at higher RPM.

I rather not yet post the information that was discussed until I try it out on my application. Things such as fuel pressure, float level consistancy, how to tune drivablility progression circuits.


However, I would like to hear how your motor is running with 48 IDAs.
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Old 01-16-2009, 07:04 AM
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My stroked 427 ran very well with the webers, but only after putting in larger chokes. I did have a very small stumble at 2300 that I never got a chance to work through before I sold the car. I found the webers to be one of the most fun parts of the car build. I always felt that if I had added a third progression hole, the stumble likely would have been gone.
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Old 01-16-2009, 07:10 AM
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Entdoc,
Thank you for your response.

One tip that was mentioned to me to help diagnosis your problem was :

If mixture for idle and main are correct

Idle your motor up to where you are experiencing the problem with idle screw. Then shut off the motor. Look at the relation of the throttle plate to the progression holes ( if I got this right) if the progression holes are under the throttle plate then additional holes could possibly help.

If the progression holes are above the throttle plate then the additional would not help.


What was the condition of your plugs. Were they burning clean?
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Old 01-16-2009, 11:49 AM
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perhaps darker than ideal , but never fouled
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Old 01-16-2009, 12:21 PM
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One thing that you should keep in the back of your mind with regard to the Mazda Rotary application is that each barrel of the IDA was virtually continuously feeding three cylinders ( chambers if you like ) firing at equal intervals. Not the same as your 1 barrel per cyl application where the inlet valve is open for say around 280°/300° of crank rotation then closed for the other 420°/440°.
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Old 01-16-2009, 02:18 PM
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exactly. I do not see how a radical cam and webers could coexist comfortably in a V8. Vacuum signal is so important in webers, any carb actually, but certainly you feel the misses more with IDA's and single feed plenums.
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Old 01-16-2009, 03:12 PM
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So what is considered to be the optimal fuel pressure to run webers?? Also is a mechanical pump inferior to using an electric pump?? A weber guy in Socal told me I should dump my mechanical and get an electric pump.
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Old 01-16-2009, 03:37 PM
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My SOHC runs great. The key was to do the final tuning on a dyno with exhaust gas analysis. My only problem is they are too small for the this motor, I did not know about the Berg IDA which is now available all the way to size 60 rather than 48:



Alan Sorkey
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Old 01-21-2009, 10:58 PM
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Quote:
Originally Posted by priobe View Post
Idle your motor up to where you are experiencing the problem with idle screw. Then shut off the motor. Look at the relation of the throttle plate to the progression holes ( if I got this right) if the progression holes are under the throttle plate then additional holes could possibly help.

If the progression holes are above the throttle plate then the additional would not help.
To make it easier still, you could leave the engine running at the high idle speed and simply turn the idle screw in a little and see if the engine gains rpm.

If the engine gains rpm, then you are too rich at that point (idle jet / air corrector combination).

If the engine looses rpm, it may be the correct idle jet / air correct combination, but proceed by now turning the mixture screw out a little.

If the engine gains rpm it needs a richer idle jet / air corrector combination.

If the engine looses rpm and the loss is comparable to the loss of rpm when you turned the mixture screw in (a comparable amount) then the idle jet / air corrector combination is likely ideal.

Basically, you can turn the idle speed up to where ever you like (within the idle / off-idle circuits range of operation) and do a rich / lean test with an idle mixture screw. Again, if leaning the mixture screw causes the engine to gain rpm, it's too rich at that point. If leaning the mixture screw causes the loose rpm it either has the correct a / f ratio or is lean - follow up by richening the mixture screw to confirm the prior diagnosis.

NOTE: you may need to lean or richen more than one mixture screw.

You must tune from the bottom up, meaning start with the idle & off-idle (transition), then work into the main circuit. The main jet size as well as the main air corrector and emulsion tube all play a part in the activation point of the main circuit - and together with the idle jet / air corrector combinaton determines the overlap between the two circuits.

Troy Patterson
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