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Discussion Starter #1
I have an '86 Vulcan and I'm experiencing 2 of the 4 cyl (right side I think) not firing and the tach would shut down. Running on 2 plugs i guess. I replaced both coils, wires, boots and started right up and ran great for a day. Thought problem was fixed, today same thing. Need help and advise please...
 

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Chucklehead
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I would check the pickup coils.
 

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FREEBIRDS MC CENTRAL NY
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2000 VN 750 Senior Member
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I think it is time to read the Vulcan Verses to possibly learn a bit about this particular machine. Since it was your first posting, Welcome.
 

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2000 VN 750 Senior Member
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FREEBIRDS MC CENTRAL NY
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..have a vulcan good day!
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I have an '86 Vulcan and I'm experiencing 2 of the 4 cyl (right side I think) not firing and the tach would shut down. Running on 2 plugs i guess. I replaced both coils, wires, boots and started right up and ran great for a day. Thought problem was fixed, today same thing. Need help and advise please...
VN750's are two cylinder engines each cylinder with two Spark Plugs.
When I lost spark to a cylinder, I replaced the Ignitor Box (CDI Box) .....fixed the problem.

EDIT: Sorry guys....just now read Posts 2-7

:smiley_th
 

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Sparky!!!
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VN750's are two cylinder engines each cylinder with two Spark Plugs.
When I lost spark to a cylinder, I replaced the Ignitor Box.....fixed the problem.

EDIT: Sorry guys....just now read Posts 2-7

:smiley_th
I don't think an ignition control box would fix the problem.. he is only loosing spark on one side... both cylinders are firing, but not on both plugs
 

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..have a vulcan good day!
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I don't think an ignotro would fix the problem.. he is only loosing spark on one side... both cylinders are firing, but not on both plugs
How's that ?
Bad Plug wires or bad plugs....right ?

:smiley_th
 

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2014 KLR 650!
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While we are off the subject, has anyone has iridium plugs just break in two when they take them off? Ive had two do that on the rear left hole. Very strange. I dont run iridium any longer. They dont seem to work as well for me.
 

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Registered
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I don't think an ignition control box would fix the problem.. he is only loosing spark on one side... both cylinders are firing, but not on both plugs

I don't think it's the pickup coils either, for the same reason.
 

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Super Moderator
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my front right would occassionally drop out..

found it to be a flakey boot, and it was arcing to the metal coil shielding the throttle cables
 

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to add, since the OP thought it was a 4 cyl and was dropping 2 cyls, he may be loosing one cylinder, and still has an issue.
 

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If he is losing fire on one plug in each cylinder, the bike should run well except at close to full throttle. Chances are he is losing one complete cylinder.

The reason for 2 plugs per cylinder is so it can run well with reduced timing. Nothing else. Total advance is something like 25*.
 

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The reason for 2 plugs per cylinder is so it can run well with reduced timing. Nothing else. .
Wouldn't have anything to do with the extra pair of valves per cyl, huh?
 

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Discussion Starter #18
did some more troubleshooting... looks like front cyl not firing. Just now attempted to start and it started fine. Tach worked idled great and then it stalled. Restarted, but had to choked to keep running. After few minutes, front cyl still cold, rear cyl warm. Tach drops off when this happens. Both coils have been replaced, but plugs not. Less than year old. Front plugs were wet when i pulled it out. Obviously not firing. Igniter???
Thanks for the input...
 

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Wouldn't have anything to do with the extra pair of valves per cyl, huh?
No. The vast majority of 4 valve heads have a single plug in between the valves. Most with larger chambers, etc. A 87 octane and 10+/1 compression engine will require reduced timing to the point of poorer performance.

The long held theory is-2 plugs, 1 each at the extremes of the chamber will require 1/2 the timing for a complete burn. An additional benefit is increased mechanical efficiency. IE, if you fire the plug 50* in advance of TDC, the engine must work against increasing/expanding gasses for 50* of rotation.
 

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Misfireing.

Try swapping your plugs from the cylinder that's dropping out to the cylinder that's firing. That will test your plugs.
 
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