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Old 07-22-2015, 03:31 PM
Bratina Bratina is offline
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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.
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Old 07-22-2015, 07:19 PM
Dave Neptune Dave Neptune is offline
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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.

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Old 07-22-2015, 10:29 PM
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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
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Old 07-22-2015, 10:34 PM
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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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Old 07-23-2015, 05:39 AM
The Garbone The Garbone is offline
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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.
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Old 07-23-2015, 09:05 AM
Bratina Bratina is offline
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Thanks, everyone, for the replies.

Quote:
Originally Posted by hanleyclifford View Post
You might also have a bad ignition wire. A new set is available from the online catalogue on this site.
Good question - I switched the ignition wires between #3 and #4 and the problem didn't follow the wires. Can I take that to mean that the wires are ok? I would have assumed that if the wires were faulty then the problem would follow the wire. They're from our host, purchased in 2013 (or early 2014).


Quote:
Originally Posted by Dave Neptune View Post
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
I will run this check when I'm next at the boat (this weekend most likely). I have to ask though - what kind of / level of insulation?! I pull the plug wires by hand and, although I'm not standing in water or anything I'm not insulated...

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
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Old 07-23-2015, 10:20 AM
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Please test your voltage at coil +, hot and running, just to eliminate that possibility.
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Old 07-23-2015, 10:46 AM
Dave Neptune Dave Neptune is offline
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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.

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Old 07-23-2015, 10:57 AM
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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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Old 07-23-2015, 03:40 PM
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Quote:
Originally Posted by JOHN COOKSON View Post
Check for corrosion in 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
That's a nice easy check - thanks. I'll pull them and take a look. If there is corrosion can I clean it up, or should I replace the cap? I'm honestly scared of messing with the distributor, any more than the 'field tuning' I ran under power by twisting it a little.

Quote:
Originally Posted by Dave Neptune View Post
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
No pacemaker for this 38 year-old, so I'll just "hold and hope"

Quote:
Originally Posted by hanleyclifford View Post
Please test your voltage at coil +, hot and running, just to eliminate that possibility.
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...
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Old 07-23-2015, 08:53 PM
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Quote:
Originally Posted by Bratina View Post
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...
Correct.
The - terminal on the coil is NOT a ground...
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Old 07-24-2015, 01:39 AM
JOHN COOKSON JOHN COOKSON is offline
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Quote:
Originally Posted by Bratina View Post
That's a nice easy check - thanks. I'll pull them and take a look. If there is corrosion can I clean it up, or should I replace the cap? I'm honestly scared of messing with the distributor, any more than the 'field tuning' I ran under power by twisting it a little.
You should check all the secondary circuit, coil->spark plugs. There may be something inside the distributor cap that is causing the spark plug misfire such as a burned rotor or burned contacts inside the distributor cap.
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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Old 07-24-2015, 01:22 PM
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Quote:
Originally Posted by JOHN COOKSON View Post
You should check all the secondary circuit, coil->spark plugs. There may be something inside the distributor cap that is causing the spark plug misfire such as a burned rotor or burned contacts inside the distributor cap.
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
Thank you, too. I have a long list of step-by-step diagnostics for this weekend. I'll report back!
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Old 07-26-2015, 05:16 PM
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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?
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Old 07-26-2015, 05:28 PM
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Quote:
Originally Posted by Bratina View Post
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?
With that kind of voltage (very close to the numbers I run on my engine) you probably do not need to run resistance spark plugs. You may be ok while the plug is new but later the problem could come back. Try using a non resistive plug. Edit: don't know if this has ben discussed, but you should know what your dwell reading is.
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Old 07-26-2015, 06:48 PM
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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
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Old 07-26-2015, 07:35 PM
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Quote:
Originally Posted by hanleyclifford View Post
With that kind of voltage (very close to the numbers I run on my engine) you probably do not need to run resistance spark plugs. You may be ok while the plug is new but later the problem could come back. Try using a non resistive plug. Edit: don't know if this has ben discussed, but you should know what your dwell reading is.
I didn't really know I was I guess that's what the R in the plug name stands for... Which plugs do you run? Admin suggested these voltages are low. Should I be looking to change anything else?
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Old 07-26-2015, 08:01 PM
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Originally Posted by Administrator View Post
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 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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Old 07-26-2015, 08:06 PM
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Quote:
Originally Posted by Bratina View Post
I didn't really know I was I guess that's what the R in the plug name stands for... Which plugs do you run? Admin suggested these voltages are low. Should I be looking to change anything else?
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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Old 07-26-2015, 08:51 PM
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Quote:
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...Admin suggested these voltages are low. Should I be looking to change anything else?
Bratina-
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.
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Old 07-26-2015, 08:57 PM
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Bratina-
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.
If there is no resistor ahead of that coil, there is indeed another problem.
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Old 07-26-2015, 09:05 PM
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Quote:
Originally Posted by hanleyclifford View Post
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.


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.
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Old 07-26-2015, 09:08 PM
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Quote:
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If there is no resistor ahead of that coil, there is indeed another problem.
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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Old 07-26-2015, 09:44 PM
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Quote:
Originally Posted by Bratina View Post
As far as I know or can see, there isn't a resistor in the circuit. What problem does that voltage point to?
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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Old 07-26-2015, 09:48 PM
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Quote:
Originally Posted by Bratina View Post
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.
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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