Weber IDA Jetting

[John Carnevale]

I have a small block Ford stroked to 331
AFR 185 heads
Comp 282S cam 236/236 @.050 .528/.528 lift 110 lobe seperation
Weber IDA's
60 idle jet
1.10 holders
f5 emulsion tubes
155 Mains
190 Airs
37mm chokes
idle screws 3/4 turn out
Fuel pressure at 2.5lbs

Plugs are black set up is running rich. In the process of switching the chokes to 40mm.

I see a lot of 331 small blocks on the site running Weber IDA's. Any one care to share their Weber jetting set up?

 

[Rob]

Hi John,
IMO: Opening the chokes up is a good first step for sure. Wouldn't be surprised if you end up dropping the jets down and changing the emulsion tubes also. With the current combo, I'm not surprised your running black plugs, would be surprised if they were fouling too.

 

[Randy V]

I have a small block Ford stroked to 331
AFR 185 heads
Comp 282S cam 236/236 @.050 .528/.528 lift 110 lobe seperation
Weber IDA's
60 idle jet
1.10 holders
f5 emulsion tubes
155 Mains
190 Airs
37mm chokes
idle screws 3/4 turn out
Fuel pressure at 2.5lbs

Plugs are black set up is running rich. In the process of switching the chokes to 40mm.

I see a lot of 331 small blocks on the site running Weber IDA's. Any one care to share their Weber jetting set up?

Hi John - Welcome to GT40s....

Here's the way mine came out on basically the same engine.

Frankly - unless you're racing the car, I don't think the larger chokes are really going to do you any good.. The guys that I've talked with that switched to the larger chokes found that they lost more on the bottom end and the driveability suffered.

Final Jetting / Air Correction after tuning on the dyno was;

F7 Emulsion tube, 145 Main Jet, 120 Air Corrector, 120 Idle Holder, 70 Idle Jet

We ran the fuel pressure at 3.5 PSI but you really don't need that much. We'll most likely dial it in to 2-2.5 PSI for the street.

This combination with a less aggressive cam than you have built 414 HP and 430 TQ on a Superflow 902 Dyno. The AF ratio was good;

Check this out - Post 33;
http://www.gt40s.com/forum/gt40-bui...cr-40-build-thread-supercar-2.html#post228888

 

[Frank]

Are you running anykind of filter screens right now?

 

[John Carnevale]

Not running any filters or screens.

Rob, any recommendations?

 

[Rob]

I'm running 145 mains w/ F11 tubes. Don't recall the rest of the numbers....would have to look em up. Your cubes are bigger than mine, but I'm running some big compression with high dome pistons. I too am running 3.5psi fuel.

 

[fostereast]

Hi,

Several thoughts, The chokes may be sized pretty well as you have them.

At first blush, the idle jets may be to large. Do you have any of the Weber books that discuss this, and give the process to determine if the idle jets are too large?

Pat Braden's book "Weber Carburetors" seems pretty good.

Also if you have room for a good set of properly sized air cleaners, I would suggest getting them.

 

[Mike Pass]

I think you are just guessing with the carb setup. You only have to have a different cam and the setup will be wrong. Why pay for all those expensive jets and tubes. Get your car to a rolling road with an operator who knows what he is doing and get it set up properly. A rolling road or dyno is the cheapest power you can buy and the fuel saving will quickly pay for for the setting up. One of our local forty owners got his car set up properly and came out with much better running, better fuel economy and the best bit .....90bhp more! I have only once been to a rolling road and come out with the same power once and that motor had been already set up by a top engine builder. Even motors set up on a dyno can change when in the different surroundings of the car especially with things like crossover manifolds which we can't run on the dyno or fuel supply issues etc. You have a very expensive piece of kit and it would be a shame if it doesn't do the numbers. You can also show people the print out graphs - real horsepower outbrags estimated hp.
Cheers
Mike

 

[fostereast]

Get your car to a rolling road with an operator who knows what he is doing and get it set up properly. A rolling road or dyno is the cheapest power you can buy and the fuel saving will quickly pay for for the setting up. Mike

This is of course good advice. However if the owner has to debug this on his own, there are some good books out there that take some of the mystery out of the Webers.

Since it is running rich and you mention how much the idle screws are turned in, it suggests the idle jets are slightly large. Also, a 37mm choke is a good starting point if you want peak power at 5,500 RPM.

I just notice your location Mike, I casually know an FE builder who might work with Webers in NY/NJ area named Tony Carey. (631)643-8834 If you need some help from a pro and do not have someone lined up, maybe Tony can help.

 

[EGLITOM]

Hey Randy

Are you sure you run a 120 Aircorrector jet. That just sounds a bit odd. Most jettings i´ve seen the aircorrector is at least a 160 up to 210.
A 120 would make a mixture very much on the rich side

Just wonder if this is not a typo

TOM

 

[Randy V]

Tom,

I have the engine here in my shop at home and am hoping to get out there today to do a little reorganization although I have apparently gone and torn my right side rotator cuff ((argh)) which leaves me half lame.. I should be able to get to this today and will disassemble and photograph for you..

 

[Mike Pass]

If you can't get to a rolling road then maybe the best thing is to get an air/fuel ratio meter. The AEM one is about£170 on Ebay in the UK - cheaper in the USA. All you need is a threaded bung welding in your exhaust for the calibrated lambda sensor which comes with the kit, an earth connection and a + feed and you get a reasonably accurate readout (0.1 of a ratio). Much better than guesswork or looking at plug colour etc. The AEM gauge has a ring of LEDs and also a central digital readout to tell you what your carbs are doing.

Cheers
Mike

 

[Randy V]

Here you go guys.. I got the best pictures I could..

I hope this helps!

 

[EGLITOM]

Thanks Randy for the effort to satisfy the "doubting Thomas".

I think there is a reason for my name

How did you arrive at this jetting with such small aircorrector.
Following the books i would have never dared to even try it.

Tom

 

[Randy V]

Hi Tom,

No worries here..
The fellow that was doing the Dyno work did all the tuning on it. He used a jet kit that came with my Weber setup and this is what he came up with. I don't think it was overly rich anywhere but will go through my paperwork again and double check..

I just remembered I had the dyno info online:

Ron has dyno tuned many engines for me and others. I trust him to do it right.
If anything, it may seem just a little lean in some areas while at 3600 RPM perhaps just a little rich?