Popping noise on acceleration?

Discussion in 'Small Block Tech' started by Capo, Jun 14, 2011.

  1. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

  2. dr

    dr Well-Known Member

    thanks
     
  3. rmstg2

    rmstg2 Gold Level Contributor

    The engine sounds like it has a steady miss as in running on 7 cylinders. Recheck your firing order. I couldn't really hear the pop but if it is a steady popping throught the carb it could be a bad intake valve or an exhaust valve that isn't opening as in a flat cam lobe or a pushrod off. I would pull the valve covers and see if evrything is working right. As mentioned a vacuum
    guage would be a good investment. Good luck.

    Bob H.
     
  4. exfarmer

    exfarmer Well-Known Member

    I agree with Bob it does sound like a steady miss which would indicate a problem with one cylinder either cam or ignition. Hard to tel from the video tho.
     
  5. Capo

    Capo Well-Known Member

    Thanks for all the replies guys, I guess I'll be taking the rocker covers off this weekend to look for a flat lobe, I'll be replacing the gas tank too, just got one as a gift today. :3gears:
     
  6. Tricolor72

    Tricolor72 Well-Known Member

    +1 here too, sounds like its running rough, I bet it shakes a little at idle. I would say start pulling plug wires before pulling valve covers
     
  7. Capo

    Capo Well-Known Member

    I've already pulled the spark plug wires out one at a time while it was idling and they're all firing, maybe it's a flat exhaust lobe?
     
  8. Tricolor72

    Tricolor72 Well-Known Member

    Not just to check for spark but to check for a bad cylinder:Smarty: If you pull a plug and there is no change in how the engine runs then you have found a dead cylinder and that would warrant further investigation into the valvetrain and a compression test:TU:
     
  9. Capo

    Capo Well-Known Member

    That's what I meant, I've already checked for bad cylinders, and I did a compression test and all the cylinders were around 75-80 psi.
     
  10. Tricolor72

    Tricolor72 Well-Known Member

    My mistake! Hopefully a vacuum reading tells the tale!:beer

    75-80? Thats no good, I just did a compression test on my 350 and I was at 180psi:shock:
     
  11. Capo

    Capo Well-Known Member

    Would doing a compression test when the engine is hot make any difference? When I did it the engine was cold.
     
  12. DaWildcat

    DaWildcat Platinum Level Contributor

    Needs to be done hot with the throttle open while cranking.

    Devon
     
  13. Capo

    Capo Well-Known Member

    Just a quick update, I went out and pulled all the spark plugs and they all have a golden brown color to them and no electrode corrosion, so I'm assuming all 8 cylinders are firing correctly and I'm not running lean.

    EDIT: I'm still planning on picking up a vacuum gauge this weekend and hooking it up.
     
  14. Capo

    Capo Well-Known Member

    Could it be that my carburetor is too small? It's a holly 350 cfm 2 bbl. I know when I had the 4v intake and q-jet on it the popping noise was way quieter. I couldn't get a vacuum gauge last weekend, I'm really short on money at the moment...
     
  15. Capo

    Capo Well-Known Member

    Bump

    Still haven't been able to get a vacuum tester, but recently when I go to start up the engine (doesn't matter if I'm starting it cold or if it's already up to temp) it makes a knocking noise the first time I rev it, then the knocking goes away.

    I hooked up a volt meter to the coil and the coil puts out about 9 volts with the ignition on and 7 when cranking, is that normal? I don't have a multimeter to check resistance.
     
  16. Tricolor72

    Tricolor72 Well-Known Member

    Try and get an oil pressure gauge on there
     
  17. smokum

    smokum Well-Known Member

    Andrew, if you have a Holley 2bbl carb. on there, that means you're using a Holley to Rochester 2bbl adapter. Like Larry said earlier in the thread, you could simply have a vacuum leak at the carb.
    Look closely at all of the mounting areas involved (carb. to adapter, adapter to manifold)-- make sure it's not installed backwards (upside down), and that there is no "daylight" showing (unsealed areas between carb/adapter/manifold.).
    Double-check that the whole assembly is tightened down correctly.
    Lastly, verify that you don't have any open (uncapped) vacuum ports. I've used that Holley 2bbl on a couple of different cars I've had over the years, and it has some ports that are not utilized in a normal installation on a factory Rochester-equipped vehicle.
    You also said you swapped intakes. Does the intake you have on there now have an EGR valve (round valve about 3 inches in diameter mounted on rear of intake)? If so, the valve could be sticking shut. I had a '73 Apollo with an EGR valve that wasn't working, and it popped exactly like yours (I DID hear the popping on your video).
    Again, double-check the easy & inexpensive things first, then move on to
    the more complicated, expensive fixes.
    Hope this helps!:TU:

    --Chris
     
  18. Capo

    Capo Well-Known Member

    Thanks for the info Chris. I'll check it out tomorrow. :)
     
  19. Capo

    Capo Well-Known Member

    I don't have an EGR Valve, and the carburetor and adapter plate seem to be installed correctly. :confused: I guess I'll have to take off the rocker covers sometime over the next few days and check for flat lobes.
     
  20. sean Buick 76

    sean Buick 76 Buick Nut

    Sounds like your carb is way to lean. Is there any way you could go back to a stock 2GC carb or to 4bb Q jet and 4bb intake. Really no advantage to the 2bb over the 4bb.

    You said you tried a Q jet on there as well and had popping, what it a Q jet from a Buick 350 engine or from another engine.
     

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