Weber 48 IDA setup.

Rune

Bronze Supporter
#1
I'm struggling with my webers . I started with chokes 42mm main 145 -F7 -air corr 120 idle .70mm this was no good, not able to put any load, run way to lean. Changed the chokes back to the original 37mm and then I had a other engine more promising, will do some load tomorrow .
What setup is a good choice on a 347 hope for 400hp up to 450 ? I'm happy if someone could send me in the right direction here. As I live in Norway there are few that have the knowledge to help me.

Rune.
 
#2
Rune, that's not a question folks will be able to easily help resolve without knowing more about your engine setup (including cam specs) and the car's intended use (street vs track). For dedicated street use, the 37mm chokes should be adequate. And remember to only change one thing at a time from baseline settings as you go through the tuning process. Also, it helps to install a wideband O2 sensor and AFR gauge to help guide you through the process.
 
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Rune

Bronze Supporter
#3
I will know more tomorrow after bench test and then I will ask my engine builder for the spec on cam and heads. The main use is street, with a trip on a track few times every year.
 

Rune

Bronze Supporter
#8
I use EGT probes and check the spark plugs often , so I feel a bit control. To day I had 435hp in test bench, but over 5000rpm the engine did not get enough fuel, so no I have ordered bigger main fuel jets and air correctors . I feel that I'm close now. Hope to see 450 in bench
 
#9
General rule ( From HP Books, Weber Carburetors, by Pat Braden ):
Venturi size x 4 = main jet.
Main jet + 60 = air correction jet.
This is always a starting point and mostly a tad lean.

Main jet is midrange rpm.
Air correction is top end of the rpm
Idle jet plays a role at the lower rpm.

Emulsion tubes, don't change them at all unless you know what you'r doing!!

You first select the main jet during mid range rpm testing between 2000 - 4000 rpm.
Then you select the air correction during 4000 - 7000 rpm testing
Idle jet is selected last and will have influence on the lower rpm till 2000 rpm.

I run a carb shop in Holland.

So with the 42 chokes:
Atleast 168 main jets & 228 air correction to start with

WIth the 37 chokes:
Atleast 148 main & 208 air correction to start with

You mostly end up with mains a tad bigger and air corrections a tad smaller.

120 air correction will starve the engine with fuel and will run pig rich in the upper rpm range.

Quads like 12.5-13.5 AFR. Don't aim for 14's AFR as they will splutter all around.
 
#10
And quad IDA Webers like a lot of initial advance, but it sounds like you're well on your way to a proper setup if you're doing it on the dyno.
 

Rune

Bronze Supporter
#12
Even if it is a long road to tune the Bolonga Webers I think it is worth it . And now I have the engine in a test bench, it is the ideal condition to tune for max power and in the middle area. The idle can be done home in driveway. I will experiment with the smallest main jets witch not will be used and drill them up if needed and the same with the air corr . one should have a full suitcase with all jets emulsion etc. to find the best tune up.

I have looked everywhere for to find how webers are tuned and some setup, all are different, so will mine be also. As long as i get the full power without run to lean and a nice run in middle rpm and idle I belive I have a good engine. I can take it back to test stand later if I need to
 
#13
Even if it is a long road to tune the Bolonga Webers I think it is worth it . And now I have the engine in a test bench, it is the ideal condition to tune for max power and in the middle area. The idle can be done home in driveway. I will experiment with the smallest main jets witch not will be used and drill them up if needed and the same with the air corr . one should have a full suitcase with all jets emulsion etc. to find the best tune up.
Your test bench, does it have a decent power brake to put any load on it or is your engine just free revvin without any load.
If its just free revvin you'r waisting your time and hurting the engine to the bone.

I get the feeling you'r working with an engine test stand....

To get the proper main jets, 5th gear 2000-4000 rpm on the highway or simulated under load on the dyno.
To get the proper air corrction, 5th gear 4000 - 7000 rpm on the highway or simulated under load on the dyno.

If you do it correct, its not a long road. I normaly handle these in an hour under proper conditions.
First priority is correct valve lash, second priority on a fully warmed up engine is synchronise the carbs with vacuum gauges and then give it some runs with an AFR monitor to see whats happening.
 

Rune

Bronze Supporter
#14
The test stand can load up to 1000hp, (no one can do test with a free spinning engine) . Since this is the first time I do this kind of job, I started with a setup I though was a fair beginning . And I had not a full cabinet with emulsion tubes ,main jet, air corr. etc. I have to think what will be the next solution, and then order some sizes higher , wait for something in the mailbox, and see if it was a hit.
 

Jac Mac

Active Member
#15
Im a bit different in regard to jetting carbs on an engine dyno, by all means use a known starting point for jet sizes and chokes. BUT for the GT40 final size should be in car & on road or track under conditions you intend to use it.
WHY? simply because the GT40 crossover exhaust is unlikely to be used during the Dyno testing and you wont be able to replicate the 'underhood' heat & airflow conditions that the car experiences on the road.
 

Rune

Bronze Supporter
#16
I do not think that my car ever will go on a track with me in pilot seat and take out all potensial from the engine. I'm to old for that. But I want to know that the engine can be run at max load without any problems, and the diff with the exhaust will not be a issue until someone want to do racing with the car. And if I later buy a AFR , I can do some fine tuning then . My goal now is a good engine to put in the car and to get it complete for registration and cruise on the road next summer.
 
#17
One thing you should check is to ensure you have a matched set of IDA’s. IDA’s of different series have different progression holes drilled in the bore by the butterfly, which changes the AFR from closed to WOT.

More than one set of IDA’s out there that don’t match......
 
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