Carb rejet

[z7199]

I have a BBC 402 pretty much stock.. I got a 850cfm Holley for it and I know it is to BIG but I was windering if I could rejet it to make it work. I plan on a cam and Heads eventually. Also any help on rejetting would be good also. I have never done or know how to do a rejet.

[68Stepbed]

First of all, BUY A BOOK on Holley carbs. It is a great reference guide to many tuning techniques. I don't suggest doing more than a jet change before getting a book.

Start with taking out the four bolts on the front bowl as pointed out in the first pic. The metering block may come off with the bowl or it may stay on the main body. If it stays with the bowl, just pull em apart. If it stays on the main body, you can change jets without pulling it off(unless you just want to).

The jets screw into the metering block as pointed out in the second pic. Make sure you use a WIDE flat blade screwdriver to remove and install them.

Just change em out and reinstall everything. Try the stock jets before changing anything. The cfm rating is the amount of air flowing through, not fuel. The jetting could be close out of the box. You don't know which way to jet until you get a baseline with everything stock.

Good luck and let us know how it's going.

[68C15]

changing the jets will only affect the WOT fuel curve. where you spend most of the time is in the transition & idle. SA designs has a book written by David Vizard. get it!! I have the ISBN # if ya want it.

[z7199]

Thanks Guys I will get that book first I guess. pics are great!!

[68C15]

he has 2 books. "how to build HP" volumes 1 & 2
vol 1 0-931472-24-5
vol 2 1-884089-14-3
I think vol 2 would be more usefull unless you are a virgin at engines & tuning. otherwise start with vol 1.

[72wascal]

It is a bit more complicated than just changing jets. You have to consider what type of carb you have, the cam, the manifold type and total compression volume to know what type of carb will work. I would also read up on specific areas and types of carbs before tweaking anything. Usually a new Holley out of the box runs pretty well, and the 850 is a standard for most BB. I run a 750 on my 331 ci and it runs fine throughout the power curve. If your having problems idling, it would be more a different problem such as diaphram, idle circuit, or bowl settings.

As 68c15 said, the jetting won't matter until the WOT fuel curve comes into play. The secondary is not effective until this time. Without seeing the carb and seeing what the symptoms are it is difficult to determine what the cure is.