[C2] 1965 Engine Miss
10-07-2018, 10:56 PM
#1
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1965 Engine Miss
Running along at about 60 mph, I feel the car jerking or a miss (don’t know the technical name) ever so slightly. It was worse until I adjusted the front Holley float but it still does it. How can I tell if it’s electrical or fuel related?
10-07-2018, 11:27 PM
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Is it speed or rpm related? Try going at the same rpm as at 60mph but in a different gear. You may be too lean and need to run a bit richer. I have to run my 63 a bit rich otherwise mine has amiss to it.
10-08-2018, 01:59 AM
#3
Pro
Does the motor run strong and smooth at WOT ?
10-08-2018, 04:58 AM
#4
When is the last time the engine had a tune up, gotta start with the simple stuff before getting involved with things you might not be familiar with.
10-08-2018, 06:07 AM
#5
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Does the car feel like a light 'bumping' and the car maintains its speed or does the ignition feel like its "breaking up" and the car stumbles ?
Sounds like "trailer hitching" to me .... a quick run with the vacuum advance disconnected and the vacuum source plugged should tell the tale. Unlike twisting on carb adjustments, this is binary (on or off and quickly reversible)...you can go on to other troubleshooting if this test still fails...
Sounds like "trailer hitching" to me .... a quick run with the vacuum advance disconnected and the vacuum source plugged should tell the tale. Unlike twisting on carb adjustments, this is binary (on or off and quickly reversible)...you can go on to other troubleshooting if this test still fails...
Last edited by Frankie the Fink; 10-08-2018 at 06:24 AM.
10-08-2018, 07:05 AM
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Okay, good idea, I’ll test for that. What do you do to richen it slightly, change out the jets?
10-08-2018, 07:22 AM
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10-08-2018, 07:26 AM
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Does the car feel like a light 'bumping' and the car maintains its speed or does the ignition feel like its "breaking up" and the car stumbles ?
Sounds like "trailer hitching" to me .... a quick run with the vacuum advance disconnected and the vacuum source plugged should tell the tale. Unlike twisting on carb adjustments, this is binary (on or off and quickly reversible)...you can go on to other troubleshooting if this test still fails...
Sounds like "trailer hitching" to me .... a quick run with the vacuum advance disconnected and the vacuum source plugged should tell the tale. Unlike twisting on carb adjustments, this is binary (on or off and quickly reversible)...you can go on to other troubleshooting if this test still fails...
10-08-2018, 07:30 AM
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10-08-2018, 08:16 AM
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If the trailer hitching test (pull and plug vacuum advance) doesn't solve it. Then I would suspect plug wires next. Been my experience that weak plug wires cause missing more at light throttle or even idle than at WOT throttle - I guess due to voltage/current sag under heavy engine load and acceleration. You might be able to diagnose this by running the car at night in darkness and watch for signs of stray arcing between wires or from wires to the engine.
10-08-2018, 08:37 AM
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If the trailer hitching test (pull and plug vacuum advance) doesn't solve it. Then I would suspect plug wires next. Been my experience that weak plug wires cause missing more at light throttle or even idle than at WOT throttle - I guess due to voltage/current sag under heavy engine load and acceleration. You might be able to diagnose this by running the car at night in darkness and watch for signs of stray arcing between wires or from wires to the engine.
10-08-2018, 09:07 AM
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10-08-2018, 09:19 AM
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I’m with Mike, if you’re running a carb those plugs look like they are running lean.
10-08-2018, 09:54 AM
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10-08-2018, 10:06 AM
#18
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That plug is about right as to heat range....it does look like the engine is burning lean...
If the vac advance test I mentioned doesn't answer the question, then I would suspect a lean surge caused by an incorrect mixture...
If the vac advance test I mentioned doesn't answer the question, then I would suspect a lean surge caused by an incorrect mixture...
10-08-2018, 10:18 AM
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Did you pull all of the plugs and inspect them or just that one? Lean conditions amplify the differences in intake runner length and can impact the plugs furthest from the carb more than those closest. If you have been running without issue and just recently noticed surging at mid-throttle, you may have been running slightly lean for a while and it has impacted your plugs.
Try Frankie’s vacuum advance test first. Be aware that you may have to reset the idle speed once you disconnect vacuum advance to keep the engine from stalling. Also, if you are running lean it could be as simple as adjusting idle mixture. The term “idle mixture” is a bit misleading as it impacts transition, overlapping with the jets to a higher rpm than idle.
Try Frankie’s vacuum advance test first. Be aware that you may have to reset the idle speed once you disconnect vacuum advance to keep the engine from stalling. Also, if you are running lean it could be as simple as adjusting idle mixture. The term “idle mixture” is a bit misleading as it impacts transition, overlapping with the jets to a higher rpm than idle.
10-08-2018, 02:06 PM
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I have a Carter/Edelbrock on mine so I can just turn the two screws on the front of the car to Richen it up some and that is what I did. As others have said by looking at your plugs it does appear you are a little bit Lean.