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Engine Stuttering under load

Discussion in '"Stock" Alpine' started by alpiner, Feb 2, 2016.

  1. alpiner

    alpiner Diamond Level Sponsor

    Just finished extensive rebuild of my Series V. New Petronix ignition system, rebuilt Stromberg CD150 carbs, all standard adjustments to timing, carbs, etc. check out O.K. Road test results in engine stuttering on accel under load and stalling when coming to a stop. Also engine idling is erratic with RPM's up and down. I know previous threads have discussed this but have found no results of potential fixes. Any one with ideas, before I bring it to a garage?
  2. alpine_64

    alpine_64 Donation Time

    Check for vac leaks at the manifold face to head, or csrb to manifold ( though idle might be OK with vac leak)

    Is the distributor secured tightly, not moving around with vibration?
  3. junkman

    junkman Gold Level Sponsor


    Are the valves adjusted properly? Over tight is a bad thing.
  4. Chuck Ingram

    Chuck Ingram Donation Time

    Two things come to mind
    One is a weak coil
    Second might be the fuel filter not letting enough fuel through which will stall the engine as well as the stuttering or weak performance.
    Also the fuel pump pressure should be checked
  5. husky drvr

    husky drvr Gold Level Sponsor

    Maybe - improperly operating pcv valve, a bad vacuum advance diaphragm, and/or, a rare possibility, there is a very fine wire on the distributor breaker plates you might want to check for continuity when you wiggle the wire.
  6. alpiner

    alpiner Diamond Level Sponsor

    Thanks guys, lots of good suggestions. I'll begin the troubleshooting process and report findings. Any possibility the voltage regulator or voltage stabilizer could be involved? They are the only electrical components I have not replaced.
  7. Bill Blue

    Bill Blue Platinum Level Sponsor

    Not really. If the problem is electrical in nature, it would be in the coil/Pertronix area. The problem with bad ignition components is they are dead mimics of a fuel problem. Hard to sort them out and don't think that electronic ignitions are immune to these issues. A tip off that it is electrical in nature is if the engine runs fine when cold, then starts to act up as it (and the electronic parts) warms up.

    Also, be aware that parts can be bad right out the box. Have bought and installed many of them. That is the reason I hate to replace working parts. I know the old one is good - the new one is unknown.

  8. RootesRooter

    RootesRooter Platinum Level Sponsor

    Did you remove the stock ballast resistor when you installed Petronix? Leaving it in seriously weakens the spark.
  9. Paul A

    Paul A Alpine Registry Curator Donation Time

    Excellent point!
  10. alpiner

    alpiner Diamond Level Sponsor

    Thanks for the additional thoughts. Yes I did eliminate the ballast resistor when I installed the Pertronix system. Before I installed the Pertronix the car was stuttering with the original distributor and coil which is why I tried the Pertronix set-up. So I'm back to troubleshooting the fuel system. To quote Winston Churchill: " when you are going through hell, keep going". I'll report on my progress or lack of.
  11. MikeH

    MikeH Platinum Level Sponsor

    Check for a cracked spark plug or even a broken electrode in the plug. I had replaced the coil, plugs, wires, cap and rotor on my RV. It started missing under load. First thought of old fuel. It checked out fine. After everything else was ruled out, found the center electrode in one of the spark plugs was in two pieces. I could pull half of it out of the plug.
  12. SoCal'beaming

    SoCal'beaming Donation Time

    Had the same problem on my SV ... turned out to be a slightly loose distributor .. also check the back and forth movement of the cam lobe on the dist. .. could be worn bushings.....

  13. RootesRooter

    RootesRooter Platinum Level Sponsor

    Any smoke? How extensive were the Stromberg rebuilds? Are they in sync? Float levels correct?
    Last edited: Feb 4, 2016
  14. alpiner

    alpiner Diamond Level Sponsor

    So I tried the carb cleaner spray troubleshooting method and found that the idle speed increases substantially when I spray the throttle shaft ends on each carburator with the engine at idle. My understanding is that the idle speed should decrease if there is a vacuum leak not increase. Is my understanding wrong? It looks like I need a rebuild of the carbs. Does anyone have a recommendation for where I can send the carbs for a proper overhaul?
  15. RootesRacer

    RootesRacer Donation Time

    Yes, your understanding is wrong(mostly).

    If you have a leak, the engine speed could go up (when the basic mixture is lean) or down (when the basic mixture is correct or slightly rich).
    The key is that the RPM changed and this signifies you have a leak.

    If you are sure that the leak is at the throttle spindles and not that you are leaking from a gasket nearby, you dont need a rebuild, you need the carbs reconditioned, which involves rebushing and possibly even replacing the spindles along with the normal rebuild.
  16. Chazbeam

    Chazbeam Silver Level Sponsor

    A spark plug wire was my criminal.

    Just had this and i had a bad spark plug wire. had pulled halve the way out ran idle fine but on load it stuttered if i backed off the gas (on load) it smoothed out..this drove me mad for days till i checked the plugs spark and had number two erratic. (used a spare plug) but you could just use a timing light and fast throttle stomp to see it too... once i fixed the wire it ran great again.

    Bill Blue is on point on this. it can mimic fuel issues. been there for days before i discovered the plug wire. It also happened once with loose connections to the coil. Also i had the supply line to the electronics ignition on the wrong side of the resistor. And this caused erratic behavior DUH on me
    Last edited: Feb 9, 2016
  17. Chazbeam

    Chazbeam Silver Level Sponsor

    rich mixture

    If the idle was rich it would increase...AIR ratio and all is important..
  18. George Coleman

    George Coleman Gold Level Sponsor

  19. JonPiz

    JonPiz Donation Time

    re stuttering

    I have the same issue on my 1600 which dies on acceleration. If I apply the gas slowly it picks up. I have run through all the suggestions but need some advice now.
    No vacuum leak
    Coil tested and fine
    New dizzy cap and leads
    new points
    timing 11 deg BTDC
    idle screw set at 1.5 turns
    weber 32/36 Main 140/135, Idle 65/55, Air 165/160, emulsion F66/F50

    As an added bit of info, it idles fine at about 800rpm but if I turn the distributor the revs rise a bit and the idle smooths out further till the timing is about 20 deg btdc and then it starts to die
  20. RootesRooter

    RootesRooter Platinum Level Sponsor

    My Weber does the same thing. It also dies when I come to a halt at anything less than fully warmed up. With a lot of choke, it starts right back up, but with the same acceleration issue. I bot a kit with accelerator pump and a variety of jets but haven't installed it yet. Looking at your jet numbers, I'm not as positive that running richer will help with my stoplight dying. I'm still hopeful the new accelerator pump will solve the acceleration issue.

    We should move this to a new thread though and let Alpiner deal with his Stromberg problems.

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