Weber tuning on 427 engine

[Hannes]

just fulfilled my boyhood dream and bought a 427 with weber 48IDAs. Unfortunately I have a real problem in getting the webers tuned.

The car previously was used in South Africa and I am not sure that here in Austria the current setup of the webers can work at all due to climatic differences.


After trying a few different jets, here is my cry for help:

can anybody recommend a good basic setup for the webers for a 427 engine, which is supposed to produce 425 hp ? unfortunately nothing is known about the exact details of the engine (cams, compression etc.).

with the original jets it ran way too rich backfiring all over the place and fouling the spark plugs real fast.

with a new set of leaner jets I got it to run well at idle and until about 3000 RPM. then its starts to backfire in all directions again, even worse than before. Going higher with the RPMs it stops backfiring but does not produce a decent power output and seems to run too lean.

currently there are 40 mm venturis installed.

any help and hints would be much appreciated.

with kind regards from Vienna

Hannes Winkler

[427Aggie]

Well I guess I get to be the first on the subject...I don't have a life

There are several posts on this that you can search through...the first thing you need to do is find out what you have...on the IDA's you have the following

Idle Jets
Idle Holders
Main Jets
Emulsion Tubes
Air Correctors
Bypass Valve - (This is down in the float bowl and you will have to take the carb apart to get
Venturis - 40 seems kind of high if you are looking for streetable verses most HP...but the altitude will make a difference..

Get that stuff and it will help everyone...I would be looking for Cal to kick in on this one..

Matt

[walt347]

Hannes, knowing the specs of your cam would be of help. Do you use any synchronizing tools ? First off all you have to go back to an initial and fully synchronized setup allowing you to find the setup your webers and your engine like.

Sorry, no better advice possible so far.

Walter

[Sal Gerace]

Hannes,
This is where a member advised me to start with the webers.
"If this car is for the street, 37mm chokes are a must; 65/120 idle/holder;
145-150 main jet; 190-200 air correction jet; F 7 etubes; 55 bypass jet
(sits in the bottom of the float chamber)."
The cam is also very important. Something about the overlap but I am not sure. I think you want to keep valve overlap on the low side with these carbs. Too much overlap and at speed you will blow raw fuel out of the carbs, that's ugly.Hopefully someone can clear this up for us. Also a good book is Weber Carbs by Pat Braden. Has a tune up section and info on all webers. Good luck and let us know how you make out, Sal.

[Mike I]

Sal is correct about the issue of cam overlap. Independent runner (IR) induction systems will always be subject to some level of reversion at wider throttle openings (fuel/air mixture spraying back out of the carb inlets), but it get's much worse as the overlap values go up. Also, stay away from split profile cams (different values for I/E). Hope this helps some.

Mike