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03-03-2022, 04:18 AM | #1 |
Senior Member
Join Date: Aug 2014
Location: North island Newzealand.
Posts: 272
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Misfire at idol
I have a 42 Mercury with a pertronic points replacement and new leads and NGK plugs, runs really well but after a long drive the other day it developed a misfire at idol like someone is switching the ignition off and back on, if i am in gear and let the the clutch out till the engine get some load and then push the clutch to the floor seems to trigger it, it dose not miss a beat under throttle,
I did notice one of the plugs has a burn mark down the side of the insulator on the outside, I tried a different cap and rotor, I gave the pilot mixture screws a twiddle, I was wondering if my vacuum brake on the dizzy witch doesn't seem to work was sometimes letting the ignition retard then advancing ? |
03-03-2022, 07:55 AM | #2 |
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Join Date: May 2010
Location: East Hartford, Ct
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Re: Misfire at idol
" NEW LEADS?" Unless you are using 'Spiro-wound resistor plug wires' there could be interference that may cause skipping.
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03-03-2022, 09:32 AM | #3 | |
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Join Date: May 2013
Location: Pa.
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Re: Misfire at idol
Quote:
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03-03-2022, 10:45 AM | #4 |
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Join Date: Dec 2013
Location: Minnesota, Florida Keys
Posts: 10,396
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Re: Misfire at idol
Some times, a new high power ignition source is not the best to be used when the rest of the system is stock. It was just not designed to carry the high voltages that these systems can produce. I had a 276 Merc in a '36 three window about 25 years ago, and installed a complete MSD setup, distributor, 6A Box, and all. That things would burn through the distributor cap coil tower in less than 1000 miles. If the engine started missing, it was time for a distributor cap replacement. I used stock GM replacement caps from NAPA (which fit the MSD distributor at less than half the price), which may have been part of the problem.
I am not saying this is your problem, just stating that one should strive for all systems to be kept in balance. Trying to push that much voltage through an otherwise stock ignition system can cause problems, much like installing a 454 Chevy against the stock transmission using an adapter plate; something's gotta give and it won't be the high tch new replacement. |
03-03-2022, 01:36 PM | #5 |
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Join Date: Jun 2014
Location: Williamsburg, VA
Posts: 1,636
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Re: Misfire at idol
If you are using the super high voltage Pertronix flamethrower coil, that could be just too much. Try switching to the blue Bosch coil. Cheap fix.
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03-03-2022, 02:20 PM | #6 |
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Join Date: Aug 2014
Location: North island Newzealand.
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Re: Misfire at idol
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I am running resistor leads because they say normal leads can create noise that interferes with the module, Would any 1.5 Ohm internal ballast coil be ok to use? |
03-12-2022, 11:39 PM | #7 |
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Join Date: Aug 2014
Location: North island Newzealand.
Posts: 272
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Re: Misfire at idol
I found the problem, i had put fiber washers under the banjo for the vacuum line to the distrubtor at the manifold end and it was loose, I put copper washers with a dab of locktite on the threads,
I need to adjust the vacuum brake for the new motor as it has a lot more vacuum |
03-12-2022, 11:43 PM | #8 |
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Join Date: May 2010
Location: MN
Posts: 7,063
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Re: Misfire at idol
I prefer idle to idol's.
Glad it worked out. |
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