Reeltales

I understand that each motor is a little different, but was hoping to get some help on jets sizes that people are using. Hoping someone has a similar setup that will allow me to get close to the correct jets size.

I have a 350 block that is using the L79 cam, Edelbrock Performer intake, 64 cc double hump heads that are using 2.02 and 1.60 valves, standard ram horn exhaust manifiolds. I just installed a holley 600 cfm 4150 carb (mechanical secondary). The carb came with a 65 jet in the primary and a 76 for the secondary. The squirters are 31 both front and back.
This is a used carb, the original jets when new were a 66 front and 76 rear. Not sure what the factory squirters were sized at.

gerry72

You're already close. It appears you have a 4776-1 or -2 from what you reference are the out of the box jetting (http://www.holley.com/data/TechServi...%20Listing.pdf)

Your primary squirter is a tad big (.028 is stock), the secondary a touch small (.032 is stock).

You might also check your pump cams to see if they are stock specification.

There has been some tuning done to this carburetor to suit the needs of its prior use and may or may not be in line with what your engine wants. The prior owner may have done other modifications and created a lot of problems with this carb and you'd certainly want to know what exactly it is that you have.

On a used carb, I always take them all the way down, inspect everything to ensure the carb isn't a hybrid (like wrong metering blocks and such), clean and rebuild it with new gaskets and bring it back to spec.

It's always easier to address carburetor tuning when you are working from a zero baseline.

I understand you are looking for someone with a similar setup to get to an initial setup, but what someone else has done may not work for your engine. It's best to tune for what your engine wants and you have to make that determination based upon driveability and evidence you get from reading spark plugs.

donyue

I'm definately not a carb expert, and to get time with a experience tuner with a dyno around here is like trying to win the lottery.

With that in mind I found a used Innovate Air Fuel ratio meter that I tested and it works good.

There is a exhaust clamp designed to hold the O2 sensor in the tailpipe so you don't have to weld in a bung in the exhaust. This also allows it to be used on other cars.

But if you choose to you can definitely weld in a bung with a plug into the exhaust if you desire.

With the A/F meter I can at least get things pretty close without guessing what the engine is doing and how rich or lean I am running.

If I want to I can log the results of the meter to my computer and analyze what changes in jets, air bleeds, fuel restrictions, and power valves etc. affect the engine performance and how.

I think this is ultimately better than trying to guess and simply just checking plugs. JMHO.

Reeltales

I did break down the carb and rebuild it. The internals looked good. I do have a 28 squirter for the front. I put the 31 in on the advice of a guy that rebuids carbs. He said from his experience the 28 was a little small. I did not know what the factory sizes were. I might try a 32 in the rear since I do not want to run lean at WOT.

I was questioning the jet sizes based on reading internet info where guys were saying the size difference between the front and the back jets should only be around 5 or 6 sizes different. I debated that since the factory has them 10 sizes different.

gerry72

You won't run lean at WOT with a smaller squirter. You're affecting only the pump shot and if you're not moving the throttle, the pump isn't pumping. When the secondary opens, you get the pump shot, then it goes into main metering which will be the secondary jets and the load enrichment from the power valve fuel channel, if you run a PV on the secondary. Also, keep in mind that altering squirter size cascades to the pump cam tuning since you change the shot volume/time relationship and arbitrarily making that change may set up a problem.

As to the narrower difference between primary and secondary jetting; some guys may have particular tuning need where that works for them. A lot of it has to do with whether the secondary has a power valve and how the emulsion wells are calibrated, but to say the carburetor was significantly incorrectly baseline calibrated by Holley makes the assumption their engineers have no idea as to what they are doing. The factory jetting should be very close to what will work on a Performer or any traditional dual plane manifold. Running this carb on a big plenum single plane or a tunnel ram and you'd have to jet it up.

The Holley is a very easy carburetor to tune, which is both the best and worst thing about them. Don't be afraid to make changes if you believe it will make the car run better, but don't make changes just to make changes.

Reeltales

Thanks for the advice. I will probably change the rear squirter to a 32 and leave the jets alone for now. They are real close to stock and since I do not run the car that hard they are probably close enough for my application.