#1
IP: 174.95.129.141
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Check the obvious, or the faulty application of Occam's Razor
I've been reading obsessively on these forums to try and solve a problem with my engine. It ran rough, and wouldn't generate above ~1600 rpm. I removed the leads to each cylinder and - lo - the engine didn't change pitch at all when I removed #4.
Fearing the worst, I added MMO, hand-cranked, and let it sit for a couple of days. I ran the engine - nothing out of #4, a cold plug/lead, where the others were hot. I switched leads. No change. I prodded valves, added MMO, cranked (yes, through-hull closed), read more online and in the Atomic Bible, and MMO-d more. No change. I decided to look in the hole of plug #3, to see if anything looked different; not much. On a whim, I put the plug for #3 in #4, and vice versa. I suspect you can guess the rest. With a new plug (RJ12C) in place, she's running like a champ! I should have checked the obvious first. With all that said, a question. Is there something I might have done that caused the plug (also a Champion RJ12C) to have failed? I used the correct socket, etc., although not a torque wrench. The plugs have ~5h on them, and were new earlier this season. #4 plug was sooty, suggesting it was running at some stage, but was wet with gas when I swapped to #3. |
The Following User Says Thank You to Bratina For This Useful Post: | ||
Administrator (07-23-2015) |
#2
IP: 71.118.13.238
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Bratina, it is not real common but I have seen many faulty (won't fire) plugs over the years and it appears that may of been your issue.
You may have a weak ign system that just would not fire a weaker plug/cylinder. Check your spark. pull the coil wire out of the cap and have someone crank the engine. When they crank hold the wire about 1/4" or less from the head or head-bolt. You should see a crisp blue spark, if not it may be time for some other checks within the ignition system. Insulate yourself and turn off the water valve while cranking. Dave Neptune |
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Vermonstah (07-26-2015) |
#3
IP: 24.138.22.213
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I've had plugs fail prior to the ones I use in the boat now. Keep a spare set aboard the boat
__________________
Mo "Odyssey" 1976 C&C 30 MKI The pessimist complains about the wind. The optimist expects it to change. The realist adjusts the sails. ...Sir William Arthur Ward. |
#4
IP: 107.0.6.242
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You might also have a bad ignition wire. A new set is available from the online catalogue on this site.
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#5
IP: 108.90.160.12
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On my old air cooled motorcycle it is common for me to replace the plug once a year, just get hard to kick start for a little bit then stops firing all together even though it looks nice. Of course I run a bit on the rich side since it is air cooled.....
How this relates, ehh, I don't know.
__________________
Gary 78' Catalina 30 #1179 www.svknotaclew.wordpress.com |
#6
IP: 159.53.110.140
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Thanks, everyone, for the replies.
Quote:
Quote:
It's a good call-out though. When I first got the boat, and knew almost nothing about the Atomic 4, I left the key 'on' for ~30 minutes after the engine stalled. The battery was almost flat when it stalled, but I guess I may have damaged the coil. I'll check the spark once I've been able to make sure I'm insulated enough |
#8
IP: 71.118.13.238
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Bratina, you can hold the wire in position with a plastic handled screw driver or rubber coated plier. I usually just hold it by hand and 99% of the time all is well and the other 1% or so I let go of the wire in a hurry~it's really no biggie.
Dave Neptune |
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Bratina (07-23-2015) |
#9
IP: 161.213.49.150
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Check for corrosionin the spark plug terminals in the towers in the distributor cap. Sometimes the little rubber boots don't work as well as they should to keep moisture out.
TRUE GRIT |
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Bratina (07-23-2015) |
#10
IP: 159.53.174.143
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Quote:
Quote:
Thanks - I will add to the list for diagnostics this weekend and report back. I'm a novice on 12V. Multimeter lead to the coil +, other lead to ground, e.g. a stud on the engine block? Sorry, that's a real basic question... |
#11
IP: 184.0.17.64
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Quote:
The - terminal on the coil is NOT a ground...
__________________
-Jerry 'Lone Ranger' 1978 RANGER 30 |
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Administrator (07-23-2015), Bratina (07-24-2015) |
#12
IP: 68.111.9.124
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Quote:
Put a piece of tape on the tower for cylinder #1 as a marker. Pull the leads off the spark plugs, loosen the screws that hold the cap on and lift the cap straight up. Remember the firing order is 1,2,4,3.You can make a dawning or take a picture before removing the distributor cap if you need a memory refresher. TRUE GRIT |
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Bratina (07-24-2015), Vermonstah (07-26-2015) |
#13
IP: 159.53.78.143
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Quote:
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#14
IP: 107.167.108.75
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Diagnostics run.
Coil+ 10.5v idle and in gear, rising to 10.9v at around 1400 rpm. What's an acceptable range? I have points. No corrosion on the tower inserts under the plug wires. I took the cap off and it looks ok. A little bit of dirt on the rotor maybe, but clean cap with no carbon trail or visible corrosion. The contacts looked like the plastic was very slightly melted. Just a tiny bit, and I have no frame of reference for how it should look. The only thing I couldn't check was for spark, since I'm at the boat on my own. I put everything back together and it all ran nicely, so at least I didn't do anything terrible taking the distributor cap off.... The engine ran well to around 1900 rpm. My prop is likely filthy (Great Lakes). Not sure if I should continue to be concerned? |
#15
IP: 107.0.6.242
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Quote:
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#16
IP: 66.249.83.189
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10.5 volts seems awfully low. Not my area of expertise (don't ask which ones are), but that doesn't seem right.
Bill |
The Following User Says Thank You to Administrator For This Useful Post: | ||
Bratina (07-26-2015) |
#17
IP: 107.167.108.62
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Quote:
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#18
IP: 107.0.6.242
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The Atomic 4 will run on as little as 9 volts. I have tested this personally and know it to be fact.
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#19
IP: 107.0.6.242
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I run both 306 and 308, no longer available so far as I know - but I don't change plugs very often. I believe J8C was once the specification but don't be bound by that. Try to run the coldest plug that doesn't foul, then go one range hotter. One thing you do need, especially with points, is a dwell meter, available for less than $20 at most auto boutiques.
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Bratina (07-26-2015) |
#20
IP: 184.0.17.64
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Quote:
I'd like to be certain... Do you have a resistor ahead of your coil? I'd like to be SURE your voltage at the coil + is accounting for any upstream resistor.
__________________
-Jerry 'Lone Ranger' 1978 RANGER 30 |
#21
IP: 107.0.6.242
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If there is no resistor ahead of that coil, there is indeed another problem.
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#22
IP: 37.228.105.28
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Quote:
Dwell meter is on the shopping list. I'll check gap next time too, should have done it today when I took the cap off. |
#23
IP: 37.228.105.28
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As far as I know or can see, there isn't a resistor in the circuit. What problem does that voltage point to?
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#24
IP: 107.0.6.242
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Typically an alternator will put out around 14 volts of which around 13 volts would be making to coil+ after going thru wires and switches etc. Since that is too much for the coil the practice is to put resistors just ahead of coil+ to bring down to 12 volts or lower. There is a formula available using Ohm's Law used by some members, but if you are below 12 volts you should be OK. Your problem seems to be that your voltage is already down there without resistors which means your alternator is not putting out enough voltage or some other problem exists in the wiring. Maybe the next step is to check voltage at Alt+ (large output terminal).
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#25
IP: 107.0.6.242
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In a new distributor specified point gap should yield specified dwell, but since the lobes are worn on our old distributors this is no longer the case. Dwell is the important specification, not gap; and you will find that correct dwell will land you at a gap setting well below specification - which is OK.
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The Following User Says Thank You to hanleyclifford For This Useful Post: | ||
Bratina (07-26-2015) |
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