So finally had time to go and pick up my Dad's old 38 Ford Pickup that was being stored up near Yosemite over Labor Day weekend. Truck has a 350/350 swap with stock cast exhaust manifolds and a Rochester 2 jet on it. No clue on the internals of the motor, I inherited the truck when my dad p***ed away in March of 2018 so I don't have any more info. On a spare block my dad had that was being stored with the truck there was a ****rel of a Holley 725 CFM 4150 carb that I grabbed and brought back home at the same time. List number on the carb is 4118-S which is apparently a service carb with a vacuum secondary that was spec'd for a Shelby 350. I say ****rel of a carb as the metering blocks are off of another carb, 5583 for the primary block and 4519 for the secondary block which from looking around came on a List 4053 780 CFM 4150. I have no clue or history on the spare block that this carb was sitting on either. Currently it is jetted with 66's in the primary metering block and 68's in the secondary metering block. A friend had a Edelbrock Performer RPM manifold sitting around collecting dust so I'm planning on mating the ****rel carb on that intake and going from there. Any advice as far as a base to start from as far as jetting if different than what is in there currently? I'm more familiar with Weber DCOE's so getting into the weeds of jetting on a Holley requires more research.
An engine is basically an air pump , air in and air out . It can only take in so much air efficiently . Holley is a bit much for 350 Cu in . , now a 750 cfm Quadra jet is the answer for a street driven car or truck .
The 66s are standard for the 600 cfm 4160s, may be just right on a stock engine. Run it and check the plugs. Joe
The guy asked for jet recommendations, not a lecture from wannabe carb experts. He already has the carb and wants to try it. He needs to look at the plugs and go from there
Upper 60's or lower 70's for starters. 725 cfm Holley's are kind of rare aren't they? Came on 1965 Shelby Mustangs and a couple other performance Fords.
I believe those had the Le Mans bowls with steel wraparound fuel line. A pic of the carb would be cool. Jetting for 4118 is 68/78. Joe
Thanks! Like I said in the beginning I'm just looking for some recommendations on where to start with jetting as this is the first time I'm dipping my toe into the pond of 4 barrel carbs. I figured this would be as good a place as any to ask since Holley carbs have been around forever and folks here have a ton of experience with them. I get that a 725 CFM carb will flow a bit much for what I am going to ***ume is a stock 350 SBC. Once I get the truck running and back on the street I do plan on upgrading bits and bobs here and there so it breathes better. I've got a 76 VW Scirocco with a set of DCOE 40's on a built 1.8L JH with headers, a hot cam and a big valve head that runs great with A/F ratios spot on where they need to be across the rev range so I understand how to tune and jet a carb. Sure thing - like I said in my original post, it's a ****rel that someone has pieced together from odds and sods:
psyko - As most always, a simple, quick trip into Google answers most all questions. Also as has been noted, a 750 is kinda large for a mostly stock 350 inch engine. Here is a list of all or most all of Holleys carburetors, stated by the "list" number. It has all of the removable parts listed by number. This includes the jet numbers, the power valve numbers, the squirter size and cam color. Along with many other items. In 90% of cases (all engine sizes!), the "OEM" jetting works just fine, especially for a stock or near stock engine. A big cam, and or big heads, may call for different parts, but this list will tell you what WAS there when the carburetor shipped. This way you'll know what to start with. https://do***ents.holley.com/techlibrary_carb_numerical_listing.pdf In case you miss it, there's a "+" sign to enlarge the pages ! Mike
The List-4053 is a '69 Z/28 Holley carb.... See if it has a GM part number stamped on the choke horn....
Metering blocks are not all the same, power valve fuel p***ages and idle restriction jets vary depending on model....a 725 cfm carb with metering blocks from an 850 for example may be over rich at low speeds...And over fuel at wide open throttle..This is why some have no luck tuning a Holley carb...
"Too big" a carb will also run lean at times. Sounds strange but it's true. One thing about jetting that @carbking should put some learnin' on us, I was told that a carburetor is ordinarily "benched and flowed" for proper jetting by good rebuilders. At this point, the carburetor could be installed on a number of different size engines and it should be very close to optimal. Or put another way, the carburetor itself determines jet size, not the engine. Mostly. Jon, does this sound right, or is this out in left field?
You asked, so will try. This is a Holley thread, and I do not consider myself qualified to give advice on Holleys, other than the 4000 series. But if the question is a general question, then: Carter would start with a "standard" size carburetor (anyone that thinks the engineers worked diligently to get such nice numbers as 500 CFM, 600 CFM, etc. probably still believes in the tooth fairy!) for modification and testing. A known set of jets would be used (remember this is a "standard" carburetor used as a starting point). The carburetor went on a flow bench and air/fuel density was measured at a number of vacuum points. Adjustments to calibrations were made, as necessary, to get the a/f density within a range. The range is necessary because each engine will have a specific fuel curve. Carter was really not interested in CFM (venturii area was used by most engineers AND enthusiasts until some marketing wag that couldn't figure area came up with CFM). If this is hard to swallow, check out some of the performance catalogues of the 1950's as to how carburetors were advertised. A test carburetor would be sent to the customer (ie Chevrolet, Pontiac, etc.) for testing on the engine. Notes would be compared, and calibrations would be adjusted, based on the needs of the designated engine. More testing would be done. Some carbs would make production, others would be discarded for one reason or another. So, with fewer words, the carb would determine the INITIAL calibration; which would be modified for the specific engine. Two things which should be stressed: (1) Carter, and the vehicle manufacturers were NOT putting a carburetor that they had on a vehicle regardless of what it was, just because they had it; and (2) "torquer" engines tend to have a TOTALLY different a/f curve than "screamer" engines. So a 350 Chevy carb, without MAJOR work, will not run halfway correctly on a 350 Pontiac engine. And yes, as you suggested, too large a carburetor will normally run lean because of low venturii air velocity UNLESS the air velocity is so low that the power circuit is engaged when it should not be (because the carb is too big), in which case too large a carb will run rich. Knowing WHY it is either rich or lean is what makes carburetor tuning enjoyable. One more thing to stress: when using a carburetor other than the stock carburetor for a basically stock engine, or any carburetor on any engine; the very best INITIAL calibration is just exactly as the carburetor manufacturer built the carburetor, to include all castings, all calibrations, everything; and then, if necessary tune from your baseline. I won't say that I have never mixed carburetor castings, because I have. But I started with known carburetors and did the mixing after careful research. And those carburetors, even though they run great with fabulous fuel economy on their present application (my shop truck) ARE ABSOLUTELY WORTHLESS for anything else. "Marriage" carburetors, depending on their state of cleanliness, make good paperweights, door stops, or just plain junk. Jon.
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