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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? |
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. |
Originally Posted by 59BlueSilver
(Post 1598119862)
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? |
Originally Posted by 59BlueSilver
(Post 1598119862)
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? |
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... |
Originally Posted by Little red 63
(Post 1598119947)
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. |
Originally Posted by rnixon
(Post 1598120211)
Does the motor run strong and smooth at WOT ?
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Originally Posted by tbarb
(Post 1598120589)
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.
https://cimg8.ibsrv.net/gimg/www.cor...e000d2ead.jpeg |
Originally Posted by Frankie the Fink
(Post 1598120875)
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... |
Originally Posted by 59BlueSilver
(Post 1598120974)
I installed new spark plugs last year, they still look good. And a new HEI module last spring. It probably could use new spark plug wires though. https://cimg8.ibsrv.net/gimg/www.cor...e000d2ead.jpeg |
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.
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Originally Posted by MikeM
(Post 1598120992)
What 1965 engine are you screwing those plugs in to and what brand/heat range are they?
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Originally Posted by DansYellow66
(Post 1598121175)
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.
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Originally Posted by 59BlueSilver
(Post 1598121264)
Not stock, AC Delco R45XLS in a ‘92 bbc with alum. bowtie heads. |
I’m with Mike, if you’re running a carb those plugs look like they are running lean. |
Originally Posted by Factoid
(Post 1598121552)
I’m with Mike, if you’re running a carb those plugs look like they are running lean. |
Originally Posted by 59BlueSilver
(Post 1598121686)
Are you guys saying I need to go to a cooler plug or enrichen the carb.? |
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... |
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. |
Originally Posted by 59BlueSilver
(Post 1598120946)
Okay, good idea, I’ll test for that. What do you do to richen it slightly, change out the jets? |
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