Interesting Weber jetting

[Eljaro]

My 48 IDA Webers I installed on my 427 FE Top Oiler have never really been set right.
The F5 emulsion tube made things a littel bit better, but not enough.
Then I took to getting rid of the popping on decelleration and installed phenolic spacers to keep the carbs cool. I also installed a return line for the gasoline in order to reliefed the fuel pressure on the needle valves after shutdown.
I got rid of the fuel boiling and dripping all over the place after shutting down the engine.
That is all fine now.
But, the transition was horrible and I could by no means cure it. I tried F5 emulsion tubes and all sorts of combinations of jets, holders and idles, to no avail.
Finally I did make a sleeve for the F5 tube, bringing the outside diameter to 8,2mm and things started getting much better. So I ordered a set of F11 tubes, which have a larger outer diameter and I got a big improvement. But it was still not good, so I went down with the idle holder sizes until a #60 holder made the transition perfect. I now have reached a point where I can say I have got it spot on..
My final setting now is:
55 idle
60 holder
F11 emulsion tube
160 Main jet
37 choke
idle screws 1 turn out
I may be able to go down with the main jet to 155 or even 150. I have to check on that. But basically I have the car running really well now, and at least in my case this is the right jetting.
I thought you weber guys might want to know, just in case some of you are not fully happy with them.

[48 IDA]

Did this cure your popping on deceleration?

Don

[ERA Chas]

Eljaro,
Thank you for sharing your hard work. Please share your cam lift, duration and LCA and if your motor displaces 427 inches or larger.
Thanks again.

[Eljaro]

The engine is a 427 FE with 427cid. The cam is a Comp 282S with gross lift of .571 and 236 duration at .50. Lobe separation is 110.
Yes, I got rid of the popping. The problem is that in order to get a good transition you usually fatten up your idle and you main jet. Anything runs on #70 idles I read somewhere and that is absolutely true.
If you follow the instructions in the weber manual as on how to find the correct idle you end up with a 70 idle jet. So you run pig rich and at medium throtle your engine hesitates and surges. That was happening to me. I also was using an enormous amount of gasoline and leaving black clowds all over the place when accellerating hard.
So I went with a 55 idle and noticed the engine going lean on transition. The #60 idle holder fattens the mixture up at the lower transition curve, and for some reason the F11 picks up from there much better than the F7 or F5 and takes you smoothly out where the main jets take over.
I also turn the idle screw out 1/2 turn more than what it should be and the popping goes AWAY.

[48 IDA]

Thanks for the infomation.

Don

[traindriver]

I also turn the idle screw out 1/2 turn more than what it should be and the popping goes AWAY.

Eljaro...I found the idle screws did the trick for popping, I am running a bit fat, may try the F11s. FYI on ebay WeberNA is selling e-tubes for about 10.50USD with shipping, best price I've seen.

Chuck

[zimmy]

Eljaro:

What air correctors are you using? I find the idle jet / holder combo interesting. Glad it works for you.

[ERA Chas]

Eljaro,

Thanks for sharing your hard work with us. Earlier I asked about your cam and size specs. Now I'd like your opinion: I have a little more "cam" than you-244/255 @.050-.613/.633 with 110 LSA. Do you think this cam could "live" with your tune?
It's ironic-you came looking for Weber expert help-now you ARE the Weber expert we're asking for help!
Thanks again.

[Eljaro]

Well Chas, I am no cam expert, but I know now that the the vacuum produced by the engine has a lot to do with the jetting and venturi size.
In my case, even with my engine having worn oil rings (the rest is ok, with 175 readings on all cylinders in a compression test) the vacuum produced was fairly high.
If you have a strong vacuum at low rpm you can go for a larger venturi size and still have enough signal to produce the correct fuel/air mixture.
When a cam has overlap it means that the two valves will be open at the same time during the final exhaust stage, which helps scavenge the exhaust gases while drawing from the intake while the piston is still moving up. That helps fill the cilinder better, but this works only from certain rpm's on up. At low rpm the response is pretty crappy, and that is why the idle with those cams is so bad.
The vacuum with those cams is comparably weak at low and medium rpm and the velocity of the air in a too large venturi will not be enough to draw the correct amount of fuel from the spray nozzle, creating bogs and hesitations in the transition.
At high rpm the engine will suck in enough air to make this work, that is why they say that for racing the larger venturi of 42mm is ok but your low and medium range will suffer.
I do not know how your cam will behave. It is not so far off my cam.You can try taking the venturi out and turning the inside to produce a 38mm innner diameter. You can try and see what happens. If it still works ok, you bore the venturi out to the next size and see again. The worst thing that can happen is that you have to buy new chokes if you overshoot.
IMHO I believe that anybody with 48IDA's on a 427 with a mild cam must be running rich with the more popular jetting and choke (37) sizes suggested in several threads in this forum.

[Eljaro]

After several hours of jet swapping and test runs I have ended up with this setting for my 48 IDA :
Main venturi 40mm
Third progression hole drilled
Idel jet 65
Idle screw 1 turn out
Idle holder 100 ( the 60 holder was too rich at cruising speeds at 2000 rpm )
Main jet 150 ( with 135 it would lean out at WOT in 4th gear at 6000rpm)
Air Corrector 120 (could go smaller but have only 7x 115 air jets)
Emulsion tube very similar to F14 (was getting lean on high rpm with F19)
Pump bypass 00 (would bog down with a .50 when stepping on the gas suddenly).
As you see, if you change one settting it affects some other, so you have to combine until you get it right.
The lambda sensor has been of great value and would have made this tuning impossible without it.
I think I have the Webers pretty well set up now. Some fine adjustment is probably still possible. I will make myself a set of 42mm venturi and see if the engine is still as responsive.
The engine now revs smoothly from idle to the limiter, and when stepping hard on the gas from say 3000 rpm in 3rd it spinns the tires.
So the 37mm venturi is probably very good for a 289 or other SB as per this link http://www.gt40s.com/forum/tech-engi...=wEBER+JETTING
but not the best choice for a BB 427.
In my case the running very rich with the popular Weber setting has ruined my rings and the car is up on the lift now to get new rings and god knows if not something else too.
Hope this has been of some help to Weber users with BB Fords.

[rlearp]

Might want to have a look at this one on venturi size:

Optimal Venturi Size for Engine Displacment

Seems to have been borne out through emperical use too.

How was power with those chokes at say 5500 plus? Does the dyno show the power flattening out? I would guess that is one torque monster due to the indivdual runners and relatively small venturi size!!!!!

Ron

[Eljaro]

Sure Ron, mathematically a 427 needs lots of air. 48 IDA with 42mm venturis will probably still be too small . Bergs 58 Weber lookalike will probably be the ideal carb. Lots of money though.
The question is which size carb and choke can a 427 digest without losing low and medium rpm flexibility and make both cruising and high speed operation compatible. For now the 40mm choke meets that compromise well.
I'll try the 42mm as soon as I have the engine back together.
Yes, it is a torque monster, not less so with the 40 chokes. Can't tell anything about dyno measurments, since all testing was done in the car driving on open road, but I could not follow the tach needle, so fast was the engine revving up. I just shifted when the MSD limiter set at 6500 came in. Seat of the pants dyno that is.
But is was pulling over 5500 like hell.
BTW It was your comments in the GT40 forum and that chart of yours that really moved me to try larger chockes than recomened (i.e. Inglese) around here.

[rlearp]

The only reason I started looking into it was transaxle limitation that demanded a high revving motor. Then, I learned of some 40 owners with 8bbl injection, 331 inch motors, and throttle bodies that were only 36mm. The owners said the motor fell over at 5000 RPM and didn't do as well as they should. Once some of these guys went to larger throttle bodies the power came on and came on strong.

I know the formulas are an approximation, and certainly not 100% accurate. But I bet you can use much larger chokes, pick up some top end poke, and not lose anything on the midrange. I'm sure a lot will depend on your intake runner volume, cam, valve sizes etc but as a rule of thumb it might not be a bad approximation to use the formulas. Only thing is it is such a pain to go through and have to change them all around for new chokes.

I'd be interested to see how she progresses, but it sound like a strong combination already!!!!

ron

[Eljaro]

Using a F7 tube with a self made sleeve to simulate F19 and F14 emulsion tubes.
Emulsion tube chart to teach myself how they work.

[Eljaro]

After the engine rebuilt, with new rings and valves the engine runs incredibly well. Plugs are light tan, engine revs up to 6500 in a blink and response is INSTANTLY. WOW !!!!!!A real race engine the 427 is now.
It idles perfectly and you can drive in heavy trafic all day without the slightest hitch.
But the tuning still goes no. Will try 42mm chokes as soon as I get a set and try my way up to the maximum, which is 45mm.
But first I have to take the engine out of the car again because a con rod bolt got loose and ruined the bearing. So new rod, new bearing and new grinding of the crank.
Keeping busy, you see.

[Cal Metal]

Nice job, Eljaro. You spent a lot of time on this. We can all learn from the experience of others.

[Brent Mills]

Eljaro, what setup did you finally end up with?

[Eljaro]

Brent,
my last drive during a rally was with this setup on the 48 IDAs:

Main venturi 40mm
Third progression hole drilled (might not be necessary)
Idler jet 65
Idle screw 1 turn out (3/4 turn only would produce too much exhaust popping)
Idle holder 100 ( the 60 holder was too rich at cruising speeds at 2000 rpm )
Main jet 150 ( with smaller jet it would lean out at WOT in 4th gear at 6000rpm)
Air Corrector 120 (larger air correctors would lean out the mixture too much at WOT)
Emulsion tube very similar to F14.
Its actually a F7 modified tube with no holes in the bottom part but only at the top. So you get aireation during the low transition (holes on top), thus leaning out there, and no holes at the bottom, which produces less aireation at the high transition band, thus richening the mixture until the main jet takes over from there.

Pump bypass 00 (would bog down with a .50 when stepping on the gas suddenly).

The car ran fantastic with this. Maybe I should try a .35 pump bypass because the sidepipes were showing black smoke when accelerating.

Finally I think I have understood how the webers work. Testing the car after every minor change and writing the result and the reading from the lambda sensor down showed some patterns. All the changes I made overlap to some degree, so I had to try all the different combinations.

Basically the changes going up the rpm scale are influenced in this order:
idle jet - idle air corrector - emulsion tube outer and inner diameter - holes on top - holes at the bottom - main jet - main air corrector , while the emulsion tube and main jet overlap in its influence and are the ones affecting the transition the most.
The light tan color of the spark plugs confirms that the mixture is now almost perfect.

But all this was only possible after I changed the main venturi to 40mm inner diameter.
With the 37mm chokes things never worked right, and the plugs were allways black, which means too rich mixture all over.
What the 37mm choke/F5-F7 emus.tube/60 air corr./ setup was doing is overly richening the transition over a broad band to go over the stumble.You are effectively pouring gasoline all over to get one spot right.

And here is a hint from Inglese in their technical primer: (giving away some crucial information btw)
Pull out those small chokes, drop in some large-diameter ones, which may be nothing more than thin-wall "sleeves", and you've got a set of 48 IDA's that will flow enough CFM to make a big block scream.

All said.
Stefan

[ENTDOC]

Stefan, I think you would need to go with a 55 bypass not 35 to decrease the over rich mixture. A 55 puts less fuel to the pump jet than a 50, is how I understand it. chuck

[Eljaro]

Chuck,
I have a 00 bypass now, not a 0.50. That means no bypass at all. The 0.50mm bypass was creating a bog, the 0.00 is good, but gives black smoke.
So a 0.35mm hole bypass is more than 00 but about 50% less than a 0.50 bypass. That should hopefully do away with the black smoke without creating a bog. Otherwise I will have to keep the 00 bypass and try something else.

Stefan