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Old 10-01-2020, 04:03 PM   #1
Standing Elk
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Default Slight high speed miss

Ok, so my 30 coupe starts very easily and runs smooth until I reach road speed, about 45 mph. At that time it seems to develop a slight miss.I have the more modern points set up installed, timing is set with a light, point gap is set with a dial indicator, spark plug gap is correct and the plugs look good. What should I be checking next? Thanks
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Old 10-01-2020, 04:08 PM   #2
Patrick L.
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Default Re: Slight high speed miss

How does it change with changes in fuel adjustment or spark lever settings ?
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Old 10-01-2020, 04:26 PM   #3
Tom Endy
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Default Re: Slight high speed miss

If you have a modern wireless lower plate installed in the distributor check to see if there is a burn mark on the slider at the position you have the spark advance set to when traveling at 45 mph.

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Old 10-01-2020, 04:32 PM   #4
Standing Elk
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Default Re: Slight high speed miss

The GAV nor the spark lever position seem to have any effect on it. When I say "slight" miss I mean you really have to pay attention to notice it but it is there.
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Old 10-01-2020, 04:33 PM   #5
Standing Elk
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Default Re: Slight high speed miss

Thanks I will have a look for that. What would cause the burn mark if it is there?
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Old 10-01-2020, 04:58 PM   #6
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Default Re: Slight high speed miss

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Loosen your gas cap and go for a drive. I had a slight miss at or above 55, I removed the cap and then no miss, even up to 70, the cruise control then said SO DOWN ! Guess who that was :-)
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Old 10-01-2020, 05:08 PM   #7
Patrick L.
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Default Re: Slight high speed miss

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Originally Posted by Standing Elk View Post
Thanks I will have a look for that. What would cause the burn mark if it is there?



Tom made a great point. The wireless plates are kinda famous for that. They tend to lose contact. A wired plate or adding a wire will correct that.
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Old 10-02-2020, 07:29 AM   #8
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Default Re: Slight high speed miss

Put some marvel mystery oil in the gas. ATF works too.
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Old 10-02-2020, 07:33 AM   #9
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Default Re: Slight high speed miss

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Tom made a great point. The wireless plates are kinda famous for that. They tend to lose contact. A wired plate or adding a wire will correct that.

X2. Personal experience, had Nu Rex wireless plates, after a while had some odd issues including the original poster's issue. Spent weeks tracking it down. Tried a jumper for troubleshooting which cured the issues. Went back to non wireless, no more problems.
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Old 10-02-2020, 09:21 AM   #10
GRutter
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Default Re: Slight high speed miss

Check your points. Open them up slightly.
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Old 10-02-2020, 10:14 AM   #11
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Default Re: Slight high speed miss

Check ferrule at end of fuel line. Must right at end of tube. Tube hits screen and restricts flow.
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Old 10-02-2020, 10:17 AM   #12
chap52
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Default Re: Slight high speed miss

"Slight high speed miss", same thing my cardiologist told me... HUH!
Couldn't resist... Chap
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Old 10-02-2020, 01:05 PM   #13
Jim Brierley
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Default Re: Slight high speed miss

Close the plug gap slightly, say to .025", and go for a test drive. This will tell you if it a weak spark, or not. I sincerely doubt it is a fuel problem. Good luck!
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