 Diagnose this blip under acceleration please |
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| s13u74cr4 |
 Oct 18 2026, 03:14 PM
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#1
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Member  Group: Members Posts: 56 Joined: 2-September 23 From: PNW Member No.: 27,558 Region Association: Pacific Northwest  |
Sometimes under acceleration I get this slight hiccup. As if for a moment it stalls. Quickly recovers, and only under acceleration. And it seems only when not fully warm. Almost like for a moment it’s fuel starved. I have replaced ALL all the fuel lines, SS lines, so I think the issue is elsewhere just don’t know where.
Link to a video. I don’t think embedding the video in a post works. Video |
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| porschetub |
Oct 18 2026, 10:24 PM
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#2
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914 Guru Group: Members Posts: 5,190 Joined: 25-July 15 From: New Zealand Member No.: 18,995 Region Association: None |
QUOTE(s13u74cr4 @ Oct 19 2026, 10:14 AM)  Sometimes under acceleration I get this slight hiccup. As if for a moment it stalls. Quickly recovers, and only under acceleration. And it seems only when not fully warm. Almost like for a moment it’s fuel starved. I have replaced ALL all the fuel lines, SS lines, so I think the issue is elsewhere just don’t know where. Link to a video. I don’t think embedding the video in a post works. Video Check your dizzy isn't gummed up on the top advance plate, after cleaning vacuum check the advance is @ full advance and not leaking ,it should hold vacuum for a reasonable amount of time can't remember off hand but 12 inHg will be enough ,the" suck on the hose trick " isn't enough for a real test, (IMG:style_emoticons/default/beer.gif) . |
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| mark04usa |
Oct 18 2026, 11:00 PM
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#3
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'70 1.7 Tangerine Group: Members Posts: 370 Joined: 14-September 09 From: Austin TX Member No.: 10,805 Region Association: Southwest Region 
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The reaction from your tachometer would indicate ignition fault.
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| emerygt350 |
Oct 19 2026, 06:35 AM
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#4
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Advanced Member Group: Members Posts: 3,794 Joined: 20-July 21 From: Upstate, NY Member No.: 25,740 Region Association: North East States |
QUOTE(mark04usa @ Oct 19 2026, 12:00 AM) The reaction from your tachometer would indicate ignition fault. Yep, what Mark said. I would check ALL of your connections to the coil, maybe it has a bad connector that loses it when the motor torques. Definitely electrical though. |
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| s13u74cr4 |
Oct 24 2026, 11:34 AM
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#5
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Member Group: Members Posts: 56 Joined: 2-September 23 From: PNW Member No.: 27,558 Region Association: Pacific Northwest |
QUOTE(porschetub @ Oct 18 2026, 09:24 PM) Check your dizzy isn't gummed up on the top advance plate, after cleaning vacuum check the advance is @ full advance and not leaking ,it should hold vacuum for a reasonable amount of time can't remember off hand but 12 inHg will be enough ,the" suck on the hose trick " isn't enough for a real test, :beer1: . I did the “trick” which I remember from my VW days and that does work. Got a vacuum gauge thing to see what the pressure is, just need to figure out how to measure it correctly. If I use a bulb to produce the suction it will hold. When I replaced the vacuum hoses I found that the place the hoses connect was actually loose on the distributor body. I tightened that up but if does not move smooth or easy really like I think it would. The PO installed a Petronix. I notice the little ground wire is essentially gone. Does it not use one?  |
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| emerygt350 |
Oct 24 2026, 12:15 PM
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#6
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Advanced Member Group: Members Posts: 3,794 Joined: 20-July 21 From: Upstate, NY Member No.: 25,740 Region Association: North East States |
It could be the pertronix unit, as that is sending the 'ground' to the coil. However, those symptoms are not what you would get from mechanical issues from the distributor like a gummy advance.
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| gereed75 |
Oct 25 2026, 10:29 AM
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#7
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Senior Member Group: Members Posts: 1,455 Joined: 19-March 13 From: Pittsburgh PA Member No.: 15,674 Region Association: North East States
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Looks like a Petronius fault to me. They can be glitchy and typically effect the tach signal as you are seeing.
They are great when working but |
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| FlacaProductions |
Oct 25 2026, 12:35 PM
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#8
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Advanced Member Group: Members Posts: 2,290 Joined: 24-November 17 From: LA Member No.: 21,628 Region Association: Southern California
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That pertronix looks like it's worth a little double-checking of the set up gap. I'd also peel that sticker off the top of it - don't need that floating around in there.
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