Interesting Weber jetting

[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.

[Eljaro]

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]

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]

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.