Another Cam and Jetting question for IDAs

markha · #1 (**permalink**) 03-05-2009, 11:11 PM

I am currently running a 347 with a Demon 750 and want to switch to 4 x 48 IDAs. I have the carbs and the chokes I have are 37s but after reading here I will bump them to at least 40s.

I am running cnc ported aluminum Avenger 215 heads.
Intake valves are 2.05
Exhaust valves are 1.6

Hydraulic Cam:
Intake lift 576 w/1.6 Rockers
Intake Duration at 050 is 234
Exhaust lift 592 w/1.6 Rockers
Exhaust Duration at 050 is 242
Advertised lobe separation is 112 but actual was blue printed at 111

So... Will it run ok with IDAs? Any thoughts on starting jetting? All these carbs came from VWs so I need some place to start for jetting. I know everyone will be different, but just need a base line. Thanks!

68gt500 · #2 (**permalink**) 03-06-2009, 01:05 AM

Since your motor is 80-100 cubes smaller than the FEs running 40mm++ Venturis, I for myself would start at the stock 37mm size and only increase them IF need arises.

Your cam should be ok. Most problems seem to come up when the lobe separation goes down toward 106 or so degrees.

The base jetting for the 48s I got was

Idle: 70
Idle holder: 120
Emulsion tube: F7
Main jet 135
Air Corrector 120
Venturis 37mm

The Accel Pump - I don´t know.

priobe · #3 (**permalink**) 03-06-2009, 07:12 AM

Here is my .02 cents for whats its worth.

Start out with the 37 chokes. This will help with the tuning with the stronger vacuum signal.

Please post what is currently in the carbs. You might be able to use what you already have without buying a whole assorment of jets ( ask me how I know).

There are many ways to get to the same result.

I would actually run

Wideband anlyzer (Important !!!!)
Syncrometer
Patients (must have)
remember keep a log of everything you do (Important !!!!)

ok now ready for jetting
120 holder
60 idle jet

Make all changes with the motor at normal temperature (Important!!!!)

50 bypass.

Concentrate on the drivablility

And did I say patients

DMXF · #4 (**permalink**) 03-06-2009, 08:14 AM

Quote:

Originally Posted by markha

I am currently running a 347 with a Demon 750 and want to switch to 4 x 48 IDAs. I have the carbs and the chokes I have are 37s but after reading here I will bump them to at least 40s.

So... Will it run ok with IDAs? Any thoughts on starting jetting? All these carbs came from VWs so I need some place to start for jetting. I know everyone will be different, but just need a base line. Thanks!

markha - Just keep in mind that the original choke size that Shelby American equipped their 289 cubic inch cars with was 42mm and you can figure the parametric similarities from there. Any ratio of choke area to cylinder displacement below that is going to hurt top end power generation capability, with the flip side that the smaller you go it makes it simpler for the average person to tune for low speed driveability. You have to find the point that you are happy with.

markha · #5 (**permalink**) 03-06-2009, 10:45 AM

Quote:

Originally Posted by priobe

<snip>
I would actually run

Wideband anlyzer (Important !!!!)
Syncrometer
Patients (must have)
<...snip>

I will be buying a Syncro. I have sync'd carbs before.
I have patients only when necessary.

On the Wideband anlyzer... which one should I use with out spending a fortune? Am I going to need to weld a bung in the exhaust for this?

priobe · #6 (**permalink**) 03-06-2009, 11:28 AM

Markha,

I use a Innovate LM1 unit. I purchased this with a the exhaust clamp. Some people dont like the clamp but it works for me.

There is a slight modification that you will to do but no biggie.

What are the jets that you have on hand?

markha · #7 (**permalink**) 03-09-2009, 12:05 AM

I have purchased my carbs used in pairs and then one additional one. So I actually have 5 IDAs right now which has proven to be handy until I can order parts. Here is the mixed bag of jets I have.

They all have 37mm Chokes and .50 throttle squirters.

Air Correctors 4 x 175 and 4 x 170 and 2 x 120
Emulsion Tubes 8 x F2 and 2 x F7
Main Jets 4 x 155 and 4 x 149 and 2 x 135

Idle Jet Holder 10 x 120
Idle Jet 6 x 60 and 4 x 55

The 149 main jets look like they were custom made. The 149 is scribed on there and it seems like a strange number.

priobe · #8 (**permalink**) 03-09-2009, 07:36 AM

ok,

I would stay with the 37 mm choke for Now.

1. order 2 more 60 idle jets
2. try the 120 holders ( more than likely you will have to solder them up and reduce the size)
3. If the 149 are truely custom, I would open them up to 155, just to get an idea.
4. Use the F2 tubes, then get or modify you air corrector so they are all 175 or purchase 200.
5. Concentrate on your idle circuit with the LM 1. Dont worry about power or higher RPM work with it until 3000 - 3500 RPM and get it right

6. You did not mention the by pass valve at the bottom of the bowl. What are they ?

7. Make sure your float is correct. This is what I do, get yourself a caliper and measure the highest point of the tang to the float bridge and work with it so .210. If you feel the main should com in a little earlier then decrease the size to .200 with max of .187

After you get your idle driving good to 3500 you can then work with the mains and air corrector.
Again this is how I did it and it works for me.

markha · #9 (**permalink**) 03-09-2009, 09:52 AM

Quote:

Originally Posted by priobe

6. You did not mention the by pass valve at the bottom of the bowl. What are they ?

After you get your idle driving good to 3500 you can then work with the mains and air corrector.

The bypass valves have no markings. It seem that I can not blow any air through them one way but can the other way. Does that mean they are 00s?

On your comment about getting the Idle Circuit figured out first, do the mains really have no impact until after 3500? I would think as soon as the butterflys start to open that the mains would begin to pull fuel, but I don't know Webers.

markha · #10 (**permalink**) 03-09-2009, 09:54 AM

Oh... also, how would I modify the jets etc. Are their drill sizes that are the same size as the different jets and correctors? Is that a stupid question?

priobe · #11 (**permalink**) 03-09-2009, 11:24 AM

markha,

Yes, it sounds like the bypasses are "00".

As for tuning. the main do come into play with the butterflies are open but only passed the transition circuit.

Actually this brings up a good point.

Look at all of your 48 IDA. Look down the barrel and you should see 2 or 3 holes. Verify that all carbs being used have the same amount of holes. How many holes do you have ?

Back to mains.

The reason why I say not to worry about the main is because you want to get the transition and drivablility down pack. When you pull off from an idle, especially with the "00" bypass you will get introduced fuel from the pump jets which can make hard to distiguish your idle circuit.

Basically , pull off slowly and and let the rpm gradually increase to about 2000 - 2500 and shift and do the same for the next gear. Once you see that this is able to respond clean, then increase the effort of movement to the gas pedal. This will help with you traveling at say "55" mph and you wanting to increase you speed slightly. You will be running off of you idle circuit at this time and your mains will probably wont be engaged at this time. The key word here would be slightly increase. If your pump jets are too large this will create a bog from too much fuel at such a low engine speed.

If you choose to use a 155 main you will probably run rich which is better than lean. You can then figure out with the LM1 if your Etube and mains are working with the right value.

markha · #12 (**permalink**) 03-09-2009, 11:36 AM

OK.. Got it. Thank you for all your help.

I drilled all the carbs for the third progression hole. Was not nearly as difficult as I thought it would be. Stuck each one in a good drill press vise and drilled a 1mm hole so that they are all in a triangle pattern.

Do you know how to drill jets? Are they just fractions of a cm or something? So is a 200 air corrector .200 of a cm? But then would a 60 idle jet be .06?

priobe · #13 (**permalink**) 03-09-2009, 01:31 PM

They are measued in millimeter. So 60 millimeter will be 6 cm

markha · #14 (**permalink**) 03-09-2009, 01:58 PM

Quote:

Originally Posted by priobe

They are measued in millimeter. So 60 millimeter will be 6 cm

hmm, but look at the hole in a 60 idle jet. I don't think that is even 1mm is it? Maybe .6 mm? I could be wrong. Guess I could try to measure them when I get home.

priobe · #15 (**permalink**) 03-09-2009, 02:00 PM

yes, sorry you are right .60

invitation · #16 (**permalink**) 03-10-2009, 10:55 PM

The Weber 48 IDA has been used for decades by VW enthusiasts whose goal it is to squeeze every ounce of performance out of their engine. Problem is, production of these coveted Webers was halted many years ago. These excellent carburetors in decent condition have become rather scarce! Typically VW motorheads (as we affectionately like to call VW performance engine fanatics) have to resort to scrounging the swap meets to find a pair of 48's and even then, they may not be lucky enough to find a pair but have to acquire them one at a time. But if you are lucky enough to acquire a set in usable condition, and you are willing put the time, money and energy into rebuilding and tuning them, you WILL be rewarded. The Weber IDA's sheer size will likely result in gasps of awe and astonishment from those that have never seen them before!

Rick Parker · #17 (**permalink**) 03-10-2009, 11:45 PM

You'll need these:
http://cgi.ebay.com/31pc-Metric-Dril...3A1%7C294%3A50

Rick Parker · #18 (**permalink**) 03-10-2009, 11:54 PM

If you chose to enlarge the jets, do it by hand using a pin vise, go very slowly. No machines should be used.