IDA Jetting Recommendation

cgilbert37 · #1 (**permalink**) 09-23-2009, 08:30 AM

Been a great many years since I had to jet a set of these, so I'm looking for some of you gurus for a much appreciated recommendation.

Combo:
351W stroked to 393ci
13.5:1 c/r
Trickflow TW heads wildly ported
Lunati cam, can't recall the grind number off hand but it's good to 6400rpm

And 48 IDAs w/42mm venturis. (Yea, I've enlargened the float bowls and drilled for the 3rd progression hole.)

Thanks!

priobe · #2 (**permalink**) 09-23-2009, 10:11 AM

cgilbert,

It would be help full if you can indicate where you are located and altitude. You need to establish a base.

What is currently in the carb?

What jets do you have?

How does it currently run.

There is no magic combo ( especially with your setup)

cgilbert37 · #3 (**permalink**) 09-23-2009, 11:08 AM

Hey thanks for the reply.
I'm in Nashville, TN- elevation is roughly 700ft MSL where I live.
No jets are in the carbs, I've had these IDAs for about 20 years on various combos and have a huge pile of jets, air correctors, and emulsion tubes.
The engine has not been run yet, I'm about to start/break-in.

I know there's no magic combo. Just looking for a starting point.

GJA GT40 · #4 (**permalink**) 09-23-2009, 08:40 PM

I have some starting point specs for you.
F7 Emulsion tubes.
175 Main jets.
160 Air correctors.
70 Idle jets.
120 Idle air jets.
300 Needle and seat.
1 Turn out on the idle mixture screw.
Should be able to start it and run on these specs then fine tune from there.
Regards--Geoff.

Nicholas Taylor · #5 (**permalink**) 01-21-2010, 05:45 AM

hi there

i'm in south africa and would like some help with a start point for my cobra with the chevy 350.

It has four Weber 40 DCOE"s. there is a flat spot between 1500 and 2000 rpm.
There coughs and splutters during cruising.

i don't know there cam's as the previous owner whom built the engine pasted away.
i'm at 1000m above sea level roughly.

Any advice?

Nic

*13* · #6 (**permalink**) 01-21-2010, 06:19 AM

How are the carbs set up now? There is some great info online. The Inglese Weber Primer is a good read as well as some books that are on the Shelf that will take you through theory & parts of the Carbs.

priobe · #7 (**permalink**) 01-21-2010, 06:43 AM

Quote:

Originally Posted by cgilbert37

And 48 IDAs w/42mm venturis. (Yea, I've enlargened the float bowls and drilled for the 3rd progression hole.)

Thanks!

Cgilbert,

If you can I would start with 37 or 40 mm chokes. This will give you a stronger signal and make it easier to tune the carbs.

However, as for a baseline I would start with

60 idle fuel
100 -120 airholder
50 bypass
4.5 pumpjet
----------------------

Do not worry about the main stack yet. get the idle circuit adjusted properly then move on to emulsion tube. This should get you up to 2000 rpm.

Next hurdle will be selecting you emulsion tube. What do you have on hand?

priobe · #8 (**permalink**) 01-21-2010, 06:45 AM

Quote:

Originally Posted by Nicholas Taylor

hi there

i'm in south africa and would like some help with a start point for my cobra with the chevy 350.

It has four Weber 40 DCOE"s. there is a flat spot between 1500 and 2000 rpm.
There coughs and splutters during cruising.

Any advice?

Nic

Make sure you have your throttle plates as closed at idle as possible without having the engine turn off.

Only concentrate on your idle circuit and make sure the carbs are synced.