No Spark at rear cylinder - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
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post #1 of 19 (permalink) Old 09-05-2010, 08:20 PM Thread Starter
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No Spark at rear cylinder

Hi,

I have a small problem with my 85 VN750, the bike starts up great, runs perfect for about 5 mins then runs on the front cylinder only.
On checking, there is gas in the carb but no spark on both plugs at rear, is this the coil breaking down or is there something else I should check? If I leave the bike for
20mins it will start OK again for 5 mins then no spark again.
Thanks in advance.

Jim
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post #2 of 19 (permalink) Old 09-06-2010, 12:03 AM
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So, what have you checked? What's your status? Do you have a manual? Do you have a multimeter? Have you checked your pickup? Is it between 355-535 Ohms? In what condition is the pickup coil connector which feeds the brain box? How many miles on the engine in what kind of environment? It could be a poor magnet in the alternator rotor if the motor has been run hot. Could be many things. Is this bike new to you? And Welcome to VN750!

The Hos '93 VN750
New fork seals, tires next
Thunderbolt '81 KZ1000 M1
Down from cam chain tensioner malfunction

My window is always down when I drive because I'd rather be on my motorcycle.

Last edited by tincanman; 09-06-2010 at 12:05 AM. Reason: Ooo! Welcome, new comer!
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post #3 of 19 (permalink) Old 09-06-2010, 01:33 AM
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Welcome to the Vulcan madness Jimshaw.
Here is a link to a free downloadable service manual:
http://www.tocmanufacturing.com/File...nd%20Parts.pdf

It is big, so save it.

I`m not a great diagnostician, but your non firing rear cylinder does sound like either a weak or no signal from the pick-up coil by the alternator, or a faulty ignition coil.

Here are mods that that can be made to both sets of coils to improve ignition, if needed.

Especially note lances post #8 for pickup coil mod:
https://www.vn750.com/forum/showthrea...on+coil+pickup

fergy`s ignition coil mod for direct 12v link to battery:
http://pages.tstar.net/~fergy/writeu...relay_mod.html

Gordon

1991 VN 750 -"Cosmic Lady" or "Bad Girl"?
Purchased May 16, 2008
Approx.19,300km (12,000 miles)

H-D windshield
Relocated R/R
MF-AGM battery
Fiamm Freeway Blaster horns
F&S luggage rack and engine guard
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July 13, 2016, Riding on the DARKSIDE now, Classic Radial 165/80-15


TOP TEN THINGS A NEW RIDER/OWNER SHOULD DO. Click on link.
https://www.vn750.com/forum/11-vn750-general-discussion/9127-top-ten-items-you-would-suggest-new-owner-do-his-new-ride.html
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post #4 of 19 (permalink) Old 09-07-2010, 11:29 PM Thread Starter
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Hi,

Some info, the bike has 27,000kms, mostly summer riding, yes I have a manual, yes I have a multimeter, no not checked pickup but shall do so this weekend, the bike is fairly new to me. I have added K&N's, rejeted carbs. It is a Canadian model. Hope this all helps.
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post #5 of 19 (permalink) Old 09-08-2010, 01:48 AM
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That does help. Multimeters and manuals are priceless. Check your dear's pickup coil's ohms while she's cold and working well, then again when she warms up and is well into her issue. Hopefully you just have a bad pickup coil. Let me know how it goes. I'm curious. Good luck!

The Hos '93 VN750
New fork seals, tires next
Thunderbolt '81 KZ1000 M1
Down from cam chain tensioner malfunction

My window is always down when I drive because I'd rather be on my motorcycle.
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post #6 of 19 (permalink) Old 09-08-2010, 06:45 AM
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Check the coil connections. Clean and reconnect them.

Welcome to the group.

02 honda sabre 1100
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post #7 of 19 (permalink) Old 09-08-2010, 09:28 PM Thread Starter
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Thanks for the help, I shall check all and report back at the weekend.
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post #8 of 19 (permalink) Old 09-10-2010, 09:59 PM
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just wondering how you tested and concluded it has no spark to rear plug? did you use a spark tester ?? the kind that light up a bulb or just took off plug wire and slapped in a spark plug and held against a ground??? just wondering.. some ppl forget they have to ground it to the engine/frame for it to spark lol

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post #9 of 19 (permalink) Old 09-11-2010, 07:20 PM Thread Starter
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hi
Tested coils hot and cold seems fine, cant seem to find how to check the pickups, any ideas greatly appreciated.
I did ground the plugs, as I said runs great for 5 mins then runs on front only, leave it to cool down and runs great again.
Weird or what!!
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post #10 of 19 (permalink) Old 09-12-2010, 01:10 AM
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sounds like the rear pickup coil is grounding out.. check it with a testlight.
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