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Projects Aftermarket carb for a 394!!

Discussion in 'The Hokey Ass Message Board' started by Dirty Olds, Feb 11, 2019.

  1. Dirty Olds
    Joined: Mar 31, 2017
    Posts: 32

    Dirty Olds

    Looking to put a aftermarket carb on my 394.....1960 Oldsmobile 98. I’m a few beers and cruise around type of guy! No speeding...just cruising. What carb would you recommend??? Thanks for all options and help!


    Sent from my iPhone using The H.A.M.B. mobile app
     
  2. saltracer219
    Joined: Sep 23, 2006
    Posts: 828

    saltracer219
    Member

    The factory Rochester 4 jet is a hard carb to beat for reliability and drivability if properly reconditioned.
     
    anthony myrick likes this.
  3. czuch
    Joined: Sep 23, 2008
    Posts: 2,688

    czuch
    Member
    from vail az

    4-Jet is good.
    I've had good luck with the Edelbrock.
     
  4. If its a 4 bbl get a adapter and bolt on a Carter AFB (Edelbrock)
     
    Clay Belt likes this.

  5. Bird man
    Joined: Dec 28, 2009
    Posts: 695

    Bird man
    Member
    from Milwaukee

    The AFB is far superior to the 4 Jet. Lighter, easier to tune and no left turn bog.
     
    Clay Belt likes this.
  6. carbking
    Joined: Dec 20, 2008
    Posts: 3,153

    carbking
    Member

    The Rochester 4-Jet is an EXCELLENT carburetor.

    The biggest disadvantage to the 4-Jet is local availability of tuning parts (if you have a non-stock engine). Second disadvantage is the dearth of tuners that understand the 4-Jet. Done right, would be great on a stock or slightly modified engine.

    The Oldsmobile and Buick engines have significantly similar fuel requirement curves, so if you really want to change, a Buick Carter AFB from the same period should run well with virtually no tuning necessary on a stock engine; and a larger universe of readily available tuning parts for a non-stock engine.

    Stay away from the original Carter aftermarket AFB's (this suggestion also applies to the various clone AFB's). The Carter aftermarket AFB's were ALL calibrated for a Chevrolet fuel curve. The Chevrolet fuel curve is TOTALLY different than what the Olds engine would like.

    Just as an example of the differences, when I installed two AFB's on my performance FE 390, I started with the original Carter Comp series carbs (I wanted these castings). I then replaced: primary venturii, secondary venturii, primary jets, secondary jets, step-up rods, step-up springs, and auxiliary air valves. Of course, I had all of these items in my inventory. How complete is your inventory of tuning parts? ;)

    EDIT: Birdman - the Rochester doesn't have the bog if the service man read the manual and installed the factory "fix" for the bog, instead of using the pages for.... ;)

    Jon.
     
    belair, saltracer219 and F&J like this.
  7. Sorry, Not true ..Well, probably lighter.
    What is the left turn bog? Never heard of it
     
  8. Paul
    Joined: Aug 29, 2002
    Posts: 15,523

    Paul
    Editor

    What's in it now?
     
  9. carbking
    Joined: Dec 20, 2008
    Posts: 3,153

    carbking
    Member

    Mark - the bog was present in early 4-Jet as well as Carter WCFB carbs. The cause was air horn gasket deterioration allowing fuel slosh in a hard turn to enter the vacuum passage controlling the automatic choke.

    Both Carter and Rochester issued service bulletins with a factory authorized "fix" about 1957~1958 (I don't remember exactly, and too lazy to look it up ;) )

    The fix was to mill the vacuum passage slightly oversize for roughly a 3/16 depth in the bowl, press a small brass bushing in the bowl, and mill the vacuum passage in the air horn to allow the bushing to fit into the air horn. This prevented slosh from allowing fuel to enter the passage. A new air horn gasket with a slightly larger diameter (to accommodate the bushing) was issued at the same time.

    Jon.
     
  10. footbrake
    Joined: Sep 3, 2009
    Posts: 110

    footbrake
    Member

    OMG back in the late sixties my first race car was a 64 Olds 98 with the 394. I had a 2"spacer and a 750dp on it. with no other changes and it took it fine.
     
  11. Thanks, Jon.
    Can't imagine a line mechanic performing this operation in his bay though. ;)
     
  12. There ya go..Reply of the week} Put a 750 DP Holley with a 2" spacer on a 60 Olds 98 cruiser..Beautiful!
     
  13. carbking
    Joined: Dec 20, 2008
    Posts: 3,153

    carbking
    Member

    Mark - in the era of the 4-Jet, Carter, Holley, and Rochester all had "carburetor schools". Generally, the larger new car dealerships would send at least one mechanic to the factory schools, and then that mechanic was the designated carburetor "fixer". The price of admission to the school included the factory Master Parts Book, with a one-year subscription for updates (renewable). While I am a wee bit too young (not much) to have attended one of the schools, I have acquired "school material" for the above companies. Somewhere, I even have the metal instructors identification button. The lead school instructor at Carter was a good friend.

    Both Carter and Rochester offered a "kit" (drill bit, bushing, and revised air horn gasket). The drill will work, however I prefer to use an end mill. Have personally done many of these when I was still rebuilding carburetors. The carburetor must be off and apart; but the modification may be accomplished using a quality drill press.

    As to the school material, it shows up on Ebay from time to time (or...... ;) ). Carter had a series of filmstrips as well as a text/work book; Holley had a series of circuit manuals which do a good job of explaining the operation of the various circuits, Rochester had a series of filmstrips with accompanying text books.

    Jon.
     
    Mark Yac and rod1 like this.
  14. Dirty Olds
    Joined: Mar 31, 2017
    Posts: 32

    Dirty Olds

  15. Bigchuck
    Joined: Oct 23, 2007
    Posts: 1,152

    Bigchuck
    Member
    from Austin, TX

  16. Paul
    Joined: Aug 29, 2002
    Posts: 15,523

    Paul
    Editor

    If you are just "driving around" you could put a stock 2 barrel manifold and Rochester carburetor on it.
    Simple, reliable and all the linkage fits.
     
  17. Why would you want to put an after-market carb on it?
     
    saltracer219 likes this.
  18. saltracer219
    Joined: Sep 23, 2006
    Posts: 828

    saltracer219
    Member

    There is no good reason to try to adapt an aftermarket carb for this application. The fix that Jon has mentioned is easily done by a qualified early carb tech. during the rebuild process. I have also rebuilt many of these 4 jets, they are excellent carbs. My advice is to have a qualified carb shop rebuild the original carb. Beware of "rebuilt" exchange carburetors!
     
    Dirty Olds likes this.
  19. Dirty Olds
    Joined: Mar 31, 2017
    Posts: 32

    Dirty Olds

    It was honestly just a question that has been bouncing around in my head and I wanted some opinions on it. Some guys had told me to take the Rochester off and put a Edel on because it’s just more reliable. The car started to hesitate a bit after I ran out of gas one time! (Had a few to many beers and wasn’t paying attention to the gage). I really think it’s a mixture issue and not the carb itself. It’s just when I brought it up around people they had there options and I was wondering what you guys had in mind. Thanks again guys!


    Sent from my iPhone using The H.A.M.B. mobile app
     
    Mark Yac and saltracer219 like this.
  20. papajohn
    Joined: Nov 2, 2006
    Posts: 886

    papajohn
    Member

    My last 60 Olds used to boil the gas in the carb. Never figured out why. Problem with an aftermarket carb is the limited space between the engine and the hood. Most carbs will require an adapter to the old square bore manifold.
     
    kidcampbell71 likes this.
  21. I see . Fair enough. But let me ask. Or rather, maybe you could ask those E-brock fans why you shouldn't just buy a kit and rebuild the carb you have. I suppose they were really suggesting is you take a new , clean carb out of a box and bolt it on. There ARE quite a few "bubble pack-ers " in this hobby , after all.
    But let's say you buy a new carb. Then, after re-bending the fuel line , adjusting the throttle and kick down linkage, re-routing the vacuum lines, and then getting it all dialed in, then one day , let's say you run it out of gas.
    It starts to hesitate. Now what? Do you fix that one , or just buy another new carb?
    Seems to me you'd want to jump in and fix the ol' car, rather than throwing new parts at it.
     

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