Stumble on idle 34 ict’s

Discussion in 'Mech Tech' started by Gooders, Jul 12, 2019.

  1. Struggling a bit with the idle still. It seems ok during warm up but seems to stumble/ miss a beat when warmed up. Got timing spot on & have experimented with jetting but no better. Valve clearances spot on. New rebuild type 4 done about 400mls since rebuild.
    Got idle at 950rpm factory spec.
    Stumbling more when sat in drive (auto) as under a bit of load.
    I know folk say don’t worry just drive it but it’s irritating in traffic & I keep shifing into N to avoid feeling the stumble. Thoughts?
  2. Have you got a balance pipe? Also mine was a bit hesitant pulling away until I teed the vacuum to the distributor to be from both carbs. Got a video somewhere of the erratic vacuum single from a single carb...

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    vwbusman likes this.
  3. Yep got a 12mm bore balance pipe & the T’d vac supply to the distributor with the anti pulse valve. As recommended by Wayoutwestie
    earlylatebay likes this.
  4. Electric pulsed solenoid clicky fuel pump and Pertronix ignitor III? (Maybe accuspark as well)
    Dwell and timing gets modulated by voltages changing at the coil positive terminal as the fuel pump pulses draws current , drops voltage at coil, engine stumbles.

    Fix is to take fuel pump via ignition switched relay and fuse directly to battery, so voltage wobbles less.

    Try points and condenser and see if its smoother.

    Also if your distributor is a bit rattly , the engine can hunt at idle as the advance rattles around, speeds up, retards, slows , advances , speeds up and so on. Worse with electronic ignition as there is no constant drag from points.
    Last edited: Jul 12, 2019
    Gooders likes this.
  5. ^^^ Thanks a few things to try :thumbsup: I will wire the fuel pump through a relay as it is the pulse type to take the load of the coil, makes sense. Its a Pertronix igniter 1. As you say if dizzy is worn could cause it. I will swap back to points & condenser to see if that gives improvement.
  6. Just got back to campsite & she has the missing a beat syndrome on idle. Tried disconnecting the elec pulse fuel pump for a few secs but made no difference, so can rule that one out.
    Really could do with getting her on an old crypton scope & check the firing voltages. When I get back home I think I will start by
    Putting the old leads on, I remember back in the day a dodgey HT lead giving this issue
  7. Back home now & found time to have a play. Started by richening idle mixture screws a tad which made a slight improvement.
    Swapped the HT leads with the originals I removed a while ago, made no improvement.
    Swapped the coil with an old one i had & this made a big difference. I would say 75% better.
    I am thinking possible coil issue or as mentioned worn distributor/ pertronix pick up scenario.
    I can live with an occasional stumble so will try it for a bit with the old coil & lead set up.
    Last edited: Jul 26, 2019

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