thebruce

I finished bolting on new heads (Trick Flow 23 deg), 1.6 roller rockers, Air-Gap RPM intake and Dynomax headers to go with my Comp Cams XE268 cam. I've got an Edelbrock Performer 600 carb on top that is currently jetted slightly lean in the primaries. The rods are stamped 7352, which is an old Edelbrock part number, so I'm not sure how lean they are. I know that this combo will need a richer mixture, but rather than just buy all the rods and jets and try 'em all out, I figured someone here would have a suggestion on where to start. Any thoughts and input would be appreciated.

Also, once I talk my roommate into digging out his digital camera, I'll post a picture of my setup which fits under the stock '74 small block hood.


:flag

Tominator

The size of your rod is .073 x .052.
1) Do you know what your jets currently are?

I would recommend picking up the Edelbrock Carburetor Calibration kit Cat. No 1479. If you have the 1406 carb I would still get the kit listed above, the cost is around $55.00 but well worth it.

I got the kit last weekend and here are my results;
1) high reving; once RPM got past 4200 RPM I got fuel starvation :sad:, switched the secondaries jets to 101 (factory is 95) it now goes to 5600 RPM before fuel starvation starts :D. When weather permits going to to switch to 104 jets and hope that gets it into the 6500 RPM range

2) Take off; was good but not perfect, switched metering rod springs to silver for best take off, tried all 5 springs and it really makes a difference in take off.

thebruce

Tominator-

Thanks for the reply. I haven't pulled the jets yet, but I guess I need to do that too, to know where my starting point is. I'll probably go ahead and buy the kit like you did, since it sounds like you got some great results. Does the kit include rods, jets, and springs?

:cheers:

gkull

IMO why buy a kit with a bunch of parts you'll never use. Summit Racing will sell you any part you think you need. You need to get the online charts or the book and understand how they are making it rich or lean.

The charts never did have the correct small step changes. They always have big 4% or bigger steps. So I figured out on an spread sheet every concievable jetting change. It's just simple math. take the formula for area. So a jet will flow so much gas through it's area minus the area of each step in the rod diameter.
http://www.1728.com/diam.htm


So .098 = area of .00754
So .052 = area of 00212 = .00542 flow under power condition with the rods up

jets are cheaper so you could buy two 100 jets for the primary

So .100 = area of .00785
minus the 52 rod .00212 = 00573 total flow.

If it's just the secondaries you want richer like tominator above. He went from .095's which are .00708 area to .104 which is .00850 area. That's more than 15% richer. which I would tend to say is two much unless the cam/manifold required it.

I found that the settings for the stock 1405 were to rich at sea level. So if you jet inbetween stock 1406 and 1405 you should be fine. Just figure out a few charted jet and rod setttings and you will understand 4 % or 8 % rich. But with a little math you can make less than 1 % changes. I worked on Edelbrock carbs for over 10 years. So if you don't understand what I'm saying e-mail me!





[Modified by gkull, 12:41 PM 1/30/2002]

gkull

I just went out to the Edelbrock sight to refresh my memory by looking at the charts.

The chart says that .095 secondary to .104 is 12% richer. The correct way to jet any carb if you have a lean Wide OPEN Throttle is to richen both pri & seconds. Because you don't want a lean mixture out of the front barrels and a super rich seconds and just hoping that it mixes well enough to average out the total fuel mixture. You can end up with the front pistons lean and the rear pistons black.

[b]Never Never make radical changes!"