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2x2 rochester 2g running rich

Discussion in 'The Hokey Ass Message Board' started by lange, Dec 15, 2012.

  1. lange
    Joined: Dec 27, 2010
    Posts: 9

    lange
    Member

    Wanted to see if I can get any help/info/opinions on my problem.I have a 2x2 rochester 2g setup on my 56 Buick.The problem I'm having is its running rich on the rear carb.itll idle good until I gave it gas,when I do give it gas it bogs down real bad then develops a miss.the front 4 plugs are good,but the rear 4 plugs are all carbon fouled.Ive changed the jets,48 in both carbs.tried a hotter plug,didn't help and the float is adjusted right.Where else should I look?power valve?both carbs currently have the power valves.Ive messed with the idle mixture screws it doesn't seem to help,they're currently all the way in.Could this be an ignition problem?thanks for any help.
     
  2. 54nomore
    Joined: Nov 5, 2012
    Posts: 137

    54nomore
    Member
    from illinois

    Generally speaking, and from my experience, if you can close the mixture screws all the way and it doesn't kill the engine:

    the throttle blades are open too far or it's taking in air from somewhere other than the mouth of the carb(s). In other words, a vacuum leak. Sounds like only the rear carb is the problem??

    hope thats some help, Ron.
     
  3. saltflats
    Joined: Aug 14, 2007
    Posts: 10,079

    saltflats
    Member
    from Missouri

    Did it usa to run fine and them fuck up or is this a new install?
     
  4. Don's Hot Rods
    Joined: Oct 7, 2005
    Posts: 8,319

    Don's Hot Rods
    Member
    from florida

    I had a running issue with exactly the same intake/carb setup on the 350 sbc in my 23. It would run ok but if I got on it then it would start to idle really rough and lope. I thought it was the back carb, but I found out it was the front one hanging up and not closing completely. After I readjusted the linkage so it would push down more positively on the front carb the problem went away.

    I would suggest you remove the linkage to the front carb entirely and drive it to see if the problem goes away. You might have to temporarily put a wire tie or string on the front carb arm to lock it completely closed so it doesn't affect your test.

    Don
     
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  5. carbking
    Joined: Dec 20, 2008
    Posts: 2,789

    carbking
    Member

    The big four:

    (1) compression test.
    (2) solid linkage or progressive?
    (3) are both carbs the same by tag number? if so, what are the tag numbers?
    (4) if solid linkage, did you synchronize the carbs?

    54nomore's comment about killing the engine is true, but a vacuum leak should cause a lean condition, not a rich one.

    Ignition voltage could be an issue.
    Ignition timing could be an issue.
    Excessive fuel pressure could be an issue.

    Jon.
     
  6. Don's Hot Rods
    Joined: Oct 7, 2005
    Posts: 8,319

    Don's Hot Rods
    Member
    from florida

    Carbking is right about the fuel pressure, I had to dial mine down to about 3 psi.

    Don
     
  7. hudson48
    Joined: Oct 16, 2007
    Posts: 2,575

    hudson48
    Member

  8. lange
    Joined: Dec 27, 2010
    Posts: 9

    lange
    Member

    wow,thanks for the responses.I did check for vacuum leaks and didnt find any,but doesnt mean there isnt one.Im running 2.5 psi fuel pressure.Havent done a compression test.Running progressive,Im not sure if the carbs are different the # on the front carb is 7042105 no idea what the rear carb is the # was ground off.Im showing my ignorance,but does that make a difference if they are different carbs?
     
  9. Don's Hot Rods
    Joined: Oct 7, 2005
    Posts: 8,319

    Don's Hot Rods
    Member
    from florida

    If they were done right the front carb should have no idle screws and is only a "dumper". Vintage Speed puts a special base plate on theirs that has no idle circuitry.

    I don't think it makes much difference if the carbs are totally matched or not, I am going to run 3 of them on the Olds engine in my rpu and I scored them from Ebay and none of them are identical. But carbking will know for sure, much better than I.

    Don
     
  10. my guess would be that in a progressive set up the 2nd carb should have it's power valve removed and the port in the base of the bowel sealed or blocked, the idle path to the base should be blocked and there should be no idle screws either. Basically that makes the 2 nd carb a dumper. This carb should have no air flowing thru it at idle. Put your hand over the throat at idle and if there is the slightest suction you have a problem. The throttle blades should seal tight.
    Be lots of opinions on this subject, manymore qualified than mine but this may give you a start.
     
  11. coupster
    Joined: May 9, 2006
    Posts: 860

    coupster
    Member
    from Oscoda Mi

    I use a tri-power set up with a "dump" style linkage to the two outside carbs. I was always finding my plugs were black when I checked them. It always acted rich. I found the small bell style air cleaners were just to restrictive and it got richer the more air it wanted. Changed to open style air cleaners and the problem went away. Might want to try running without air cleaners if you have'nt already.
     

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