2V Tuning on a Stock 350

Discussion in 'Other' started by online170, May 13, 2010.

  1. online170

    online170 Well-Known Member

    So im pretty good with tuning a holley, an edelbrock and somewhat a Q-jet, but ive never had a 2V before.

    For all intents and purposes, the engine is a stock 1971 (possibly 70) 350 2V. It runs pretty strong, good compression, no oil burning, etc etc. Points ignition, and Accell 8mm yellow wires (could be replaced, some are cracked). Stock air cleaner, with the thermac system still hooked up.

    When the car is cold, it idles pretty low, and unless it is 100% warmed up, its horrible to drive. Once warmed up, the idle settles out at about 1000rpm. I know thats high, but i hate waiting like 15-20 mins for it to warm up. Part throttle under any type of big load, the car kinda coughs like it swallowed its tongue and wants to die. To get over this, i have to basically punch the throttle, and it lunges forward with lots of torque and sorts itself out. Additionally, it sounds like it knocks under those part throttle conditions when the revs are below 2000 rpm (basically all the time).

    A little while ago, i damagd the thermac tin foil stuff, so there was a big hole in it, and extra air was getting into the air cleaner, the problem was further worsened.

    It seems to me its too lean, and that punching it squirts fuel in from the "pump cam" which adds enough fuel and it gets going.

    Its not too bad on a very hot 25*C ++ day, but when its only a few degrees colder it gets to be annoying. Basically fall and spring time in Canada.


    How do i tune it? If it were a holley, id rejet it, but i dont know anything about the 2V, or where to get parts, or anything. The engine is going to be swapped out soon for a BBB, but i still drive it quite a bit, and would like to solve the problem.
     
  2. ap1672

    ap1672 Silver Level contributor

    Are you sure you don't have a vacuum leak? Are you sure the ignition (plugs,wires,cap,rotor,points) are good shape. The dwell and timing are set.
    You turned up the idle to 1000rpm. Will the engine warmed up idle at 700 in park smoothly?
     
  3. online170

    online170 Well-Known Member

    I dont think its a vacuum leak.

    The symptoms all go away when the car is warm, or if its a warm day.

    The plugs, wires and general tuneup are probably needed, but its not the cause of the problems.

    I will agree that timing is off slightly, and the ignition seems a little more out of tune than it was before the winter, but ive had the carb issues since day 1 (i bought it in september 09).

    The car idles fine, it never dies.

    Coldish it idles at 800rpm, 550/600 in gear.
    Warm it idles at 1000 (after i fixed the thermac), 550/600 in gear.

    I turned up the idle before fixing the thermac system, but now that i have fixed it, it idles high. If i remove the heat riser tube, it will idle at 800/600 again.

    If i just start the car, wait 10 seconds, and put it in gear, it will idle at about 300-400rpm, and still move. It never stalls, just the driveability sucks. I just find it annoying that if i dont wait 15-20 mins for it to warm up, i have to drive it at 1/8 throttle, or 3/4 throttle. Too slow, and way too fast respectively.

    I just wanna start it up, wait 5 mins and be on my way.
     
  4. sean Buick 76

    sean Buick 76 Buick Nut Staff Member

    Have you tried to set the idle mixture screws to get highest vacuum when in gear with wheels blocked and vacuum advance disconnected and plugged?

    Set the timing first then set the idle mixture screws and idle speed.
     
  5. online170

    online170 Well-Known Member

    no i havent.

    Thats sorta what i was asking, how do i do that?
     
  6. online170

    online170 Well-Known Member

    Found the mixture screws. Turned them both out about 1.5 turns. Turned the idle back down to 800.

    Idles beautifully at 600 in gear, and feels much better now. Dont know how it will behave when first started after the cold, but even with this little bit of tuning when warm i could feel a big difference in the drive.

    Not completely solved though. Before i had the "cough" from off idle to part throttle below 2000. The off idle is much better now, but the cough is still there at part throttle.

    Any more suggetions?
     
  7. sean Buick 76

    sean Buick 76 Buick Nut Staff Member

    The transition from idle to part throttle is the most important time for those carbs, without a smooth transition performance sucks.

    Now go back and set the initial timing to spec, use this as a baseline and experiment with 1 or 2 two degrees of base timing. Find out what the engine likes, keep a log book of your adjustments and change only one thing at a time. I also suggest using a vacuum gauge to look at while you adjust the idle mixture screws to get highest vacuum in gear with vacuum advance disconnected and hose plugged. Find a vacuum line that has vacuum at idle (manifold vaccum) to use for this procedure.

    The change you have made to the idle mixture screw have leaned your idle which has helped however it is not optimized. Keep in mind that if you change the timing more than 1 degree then the air/fuel requirements change so re-set the idle mixture screws. You will have to remember to lower the idle speed using the idle speed screw as the idle mixture screws get to the optimum setting. Going back and forth with these adjustments and recording your improvements as you go will get the most out of a stock engine.
     
  8. Schurkey

    Schurkey Silver Level contributor

    Lean over the driver's side fender. Remove air cleaner. Grab fuel tube near where it screws into carb. WATCH CARB while you push and pull on the fuel tube.

    Result: Almost guaranteed that the carb wiggles back and forth. Probably without much effort on your part. Loose carb screws are EPIDEMIC on the 2-barrel carbs.

    When (if) the carb wiggles back and forth, look at the idle speed screw/throttle linkage. You'll see it also wiggling back and forth. You'll never get a stable idle speed when the carb is loose like that.

    The only way to fix this is to tighten the carb screws from the throttle body to the float bowl, which means that the carb comes off for access. As long as it's off, you might as well buy a carb kit (about twenty bucks) and rebuild the carb. Might want to get a float as well. A couple of cans of aerosol carb spray should be enough to clean the carb; and spraying through all the fuel and air passages assures that they're not plugged.
     
  9. Cliff R

    Cliff R Well-Known Member

    Once you have completed a tune-up, and verified no vacuum leaks, etc, it may help to increase the primary jet size one or two numbers. It's pretty common to have to do this with those carburetors, especially with modern fuel blends, as they contain less energy than fuels we had available years ago when those engines were produced.

    I would also verify that the power valve assembly is clean and working correctly while the top is off the car, and that the accellerator pump has a viton seal on it.

    Another BIG problem with 2GC carburetors, is leaking check balls in the accl pump inlet (if used), and on the pressure side under the booster assembly. Gently seat a used steel check ball into each location and verify leak free with some fuel or solvent, before putting the top back in place.

    We stock all 2GC jets from .065" to .077".....Cliff
     
  10. Tricolor72

    Tricolor72 Well-Known Member

    Good post, I have the same issue, nice to know its definitely fuel related!
     

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