Interesting Weber jetting

Eljaro · #1 (**permalink**) 11-20-2006, 03:09 PM

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 · #2 (**permalink**) 11-20-2006, 03:26 PM

Did this cure your popping on deceleration?

Don

ERA Chas · #3 (**permalink**) 11-20-2006, 03:26 PM

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 · #4 (**permalink**) 11-20-2006, 03:54 PM

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 · #5 (**permalink**) 11-20-2006, 04:46 PM

Thanks for the infomation.

Don

traindriver · #6 (**permalink**) 11-20-2006, 06:49 PM

Quote:

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 · #7 (**permalink**) 11-20-2006, 08:28 PM

Eljaro:

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

Eljaro · #8 (**permalink**) 11-21-2006, 02:23 PM

Air correctors are 210 right now, but as I said I still have to check on the main circuit to see if its ok. I will take the car out one of these days and run it at 4000rpm for a while and then shut off with no idling to look at the colour of the plugs. They look light gray right now, whereas they were black all the time before.
The engine revs up to 7000rpm with no effort, so it may even allow for a larger air corrector jet.
I am also ordering #50 idle jets to see if it still runs ok with them. The Lambda sensor I have installed in one of the exhausts still shows rich with the #55 idle jet.
As for the emulsion tubes I would like to try out the F9 and F16 also. Maybe I will modify the F5 to make it similar to one of these two. and see what happens.
As you see testing keeps going on.

Eljaro · #9 (**permalink**) 12-09-2006, 02:23 PM

My 48 IDA on the 427 C/O are behaving much better now.
I have the #60 idle jet wit the #60 idle holder which seems to be definitively the best option.
The emulsion tube is self made.
Actually it is a F7 sleeved to have a larger outer diameter (8.2mm) and the inside drilled out to 3.5mm with all the holes an F19 tube has, only 4 more at the middle position.
So it is an F19 emulsion tube with 8 holes at the 3rd row from the bottom instead of 4.
The main jets are 125 and the air corrector 135.
Strange jetting that is, but my O2 sensor still shows rich all over the range, even on WOT.
It did lean out at WOT when fitting the 200 air corrector. I have not tried anything intermediate because I dont have any.
And now what. Even smaller main jets?
I am thinking that the signal is too strong and it is drawing too much fuel for the air the 37 main venturi lets the engine breathe.
Would a larger main venturi, say 39 or 40 lean out the mixture and get the air fuel ratio to a correct value?
I have an Os sensor welded in the exhaust where the four headers meet and I am monitoring always when driving and with load on the engine.
The engine is pulling very strong, revving up to 7000 with absolutely no hesitation at any RPM range.
Unfortunately all the driving before with the over rich condition has damaged my rings and I will have to replace those. But before I do that I want to get the Webers tuned right.
I would appreciate any help from the Weber specialists here.

Eljaro · #10 (**permalink**) 12-16-2006, 10:34 AM

Here I am answering myself again!
I want you Weber users know how my tuning is going on.
Remember that I am using Lamda sensor welded into the exhaust and I am checking on it all the time.
Took the Cobra out today(sunshine and beautiful weather here) to test the new 40mm venturis. I just bored out the 37mm ones on the lathe.

WOW! What a difference in top end power.
Perfect transition also, no strange spots anywhere, revs up to the limiter like a rocket.
I always considered that the basic Weber jettings which are mentioned in other threads was for a 289 cid engine and a 427 should needs more breathing.
I have the 48IDA Webers now jetted with:
60 Idle
60 idle holders (definitely the best option)
F19 similar tubes (F11 did worse, didn't try F5 )
145 main jet (140 might be better, have to try tomorrow)
130 air corrector (still going slightly leaner at top end , may try 125 or less).
The 55 pump bypass will have to come out for the closed one (ping and hesitation when going full on the throttle from slow speed ).

This setup was used today on a 700m stretch of 4 lane road with very light traffic, no cops and a bus stop where to park the car and make jet changes. Top speed reached 140mph before having to brake hard before the next roundabout.
The 37mm venturi may run on any engine and make everybody happy, but getting more out of the 427Fe with larger chokes without compromising drivebility is absolutely possible.

ERA Chas · #11 (**permalink**) 12-16-2006, 01:15 PM

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 · #12 (**permalink**) 12-16-2006, 04:38 PM

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 · #13 (**permalink**) 12-18-2006, 03:23 PM

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 · #14 (**permalink**) 12-18-2006, 03:46 PM

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 · #15 (**permalink**) 12-18-2006, 04:06 PM

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 · #16 (**permalink**) 12-18-2006, 05:48 PM

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 · #17 (**permalink**) 12-20-2006, 04:14 PM

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 · #18 (**permalink**) 03-31-2007, 02:54 PM

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 · #19 (**permalink**) 04-14-2007, 05:54 AM

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

Brent Mills · #20 (**permalink**) 04-14-2007, 09:54 AM

Eljaro, what setup did you finally end up with?