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Old 11-02-2015, 10:16 PM   #1
Mad Mac
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Default "Missing"

Hi again guys:
My 1929 RPU has started to "miss" a bit, especially when not fully warmed up. I have just recently filed and re-gapped the ignition points, re-timed the engine and cleaned and re-gapped the plugs, so all should be OK. What is the most common cause of "missing"?
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Old 11-02-2015, 10:26 PM   #2
Tom Wesenberg
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Default Re: "Missing"

Weak or lost spark and poor or lack of fuel are main causes of a miss. Hold the coil wire a bit out of the cap and check for a hot consistent spark.
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Old 11-03-2015, 05:49 AM   #3
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Default Re: "Missing"

see if you can determine which hole is missing by shorting them out, then focus your attention on that particular cylinder... spark plug, intake gasket, etc , etc
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Old 11-03-2015, 08:46 AM   #4
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Default Re: "Missing"

Even a "cleaned" plug might be defective ! Plugs are an expendable, wear out item. Always keep 1 or 2 sets of new plugs in stock. Even the CHEEPER brands of plugs work well, IF YOU USE THE RIGHT HEAT RANGE! Folks that drive with a little "GUSTO" usually don't have a "SOOTING" UP problem.
If you've ever used those old Champion Spark Plug Testers, then you KNOW the things that can go WRONG, up inside the plug, that can cause MIS-FIRING. Throw away old questionable plugs/condoms, so you're NOT tempted to use them again!
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Old 11-03-2015, 08:50 AM   #5
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Default Re: "Missing"

Quote:
Originally Posted by BILL WILLIAMSON View Post
Even a "cleaned" plug might be defective ! Plugs are an expendable, wear out item. Always keep 1 or 2 sets of new plugs in stock. Even the CHEEPER brands of plugs work well, IF YOU USE THE RIGHT HEAT RANGE! Folks that drive with a little "GUSTO" usually don't have a "SOOTING" UP problem.
If you've ever used those old Champion Spark Plug Testers, then you KNOW the things that can go WRONG, up inside the plug, that can cause MIS-FIRING. Throw away old questionable plugs/condoms, so you're NOT tempted to use them again!
Bill W.
throw away the used condoms also? you never taught me that
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Old 11-03-2015, 02:04 PM   #6
Big hammer
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New plugs can miss fire - if the counter person slams them down say thanks and buy them elsewhere! Or if someone hits them with a big hammer :-)
Beat you to it Bill !
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Old 11-03-2015, 07:47 PM   #7
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Default Re: "Missing"

If it has been sitting for a while you could have a stuck valve not closing all the way
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Old 11-04-2015, 12:50 AM   #8
Mad Mac
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Default Re: "Missing"

Maybe I should clarify: The "missing" does not happen all the time, so it cannot be a stuck valve. There is plenty of spark, so that is not the problem either. Engine runs quite smoothly most of the time, with only the occasional "miss".
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Old 11-04-2015, 11:06 AM   #9
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Default Re: "Missing"

May be running a tad lean, try enriching it about 1/8th of a turn.
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Old 11-04-2015, 01:11 PM   #10
George Miller
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Default Re: "Missing"

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Originally Posted by tbirdtbird View Post
if a head gasket is letting any water into the cylinder a missfire will result
That would be my guess also.
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