Wierd intermittant syndrome - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
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post #1 of 25 (permalink) Old 08-17-2006, 11:38 AM Thread Starter
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Wierd intermittant syndrome

Hi VN750 forums:

I'm a new member and I was referred to this forum to see if anyone had experience with this problem. I'll try to briefly explain, but like most electrical problems, it takes some explaining.

My 86 VN 750 would fire up and run fine for about 30 sec. then rear cylinder would not fire. It is not fuel related, i checked the spark and when it fires it gets a strong blue spark. After running on one cyl for a few miles it would usually suddenly kick back in (sometimes very exciting) and run on both for the duration of the ride. As I tried to diagnose, I lived with this pattern, but now cyl #2 does not come to life after warming up. To see if the coil was the problem I reversed the front and rear coil to see if the problem migrated to the other cylinder. It didn't - but remained on the rear cyl.

I finally determined that the rear pick up coil is defective and bought a new set of pick up coils, which I started to install last night. My Haynes manual said that I could change pickup coils by removing the outer alternator cover and tracing the wires back to the harness. Unfortunately, the shop manual says the first step is to remove the engine. Yikes. I took off the outer alt cover and sure enough, there was all the access I needed to replace the pick ups, but the wire runs through a slot in the inner alt cover and it is partially blocked by the frame, so it appears that the shop manual is correct. My question is, has anyone replaced these and do you know a shortcut to get that wire through the slot (maybe loosen the inside alt bolts to squeeze the wires through?). I am a willing but overall untallented mechanic. Also short on $ so I don't want to pay the local shop to do the job.

By the way, I have replaced the spark plug wires, battery and cleaned the terminals. When the #2 cylinder kicked in the bike ran great. Any suggestions?
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post #2 of 25 (permalink) Old 08-17-2006, 06:08 PM
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I had to go look at it. Yep, that's a bummer. What is the plug like on the other end of the wires? If you can get to the hole, you may be able to take the wires out of the plug, feed them through the hole, and then plug them back in. It may be of use to push some sort of guide wire in from the outside of the hole that you could tape your wires to, and pull back through, like fish tape.

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post #3 of 25 (permalink) Old 08-17-2006, 07:12 PM
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Well i am about to yank my engine this weekend to get to the stator. I dont think its gonna be that bad, just some labor. Now how did you figure it was the pick up coil? My first guess would have been the rear carb gunked up, and i would have run some sea foam since it is an '86.

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post #4 of 25 (permalink) Old 08-17-2006, 08:13 PM
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If youhave spark then why are you putting in pick up coils.I dont get it. I use to work on small engines . lawnmowers chainsaws etc.etc.And if you have spark all you need is air and fuel and it will run...KRAWDAD7..
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post #5 of 25 (permalink) Old 08-17-2006, 08:23 PM
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I think the key, Krawdad, is *when* the spark fires it is strong, not that the spark fires every time.

Yes, I too am curious as to how he figured out it is the pickup coil. Guess it could be a resistance (or lack of) in the coil.

It does sound like carb, though. SeaFoam would take care of that.

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Last edited by cegodsey; 08-17-2006 at 08:26 PM.
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post #6 of 25 (permalink) Old 08-17-2006, 09:05 PM
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Can you use the old wires as pull wires for the new stuff? solder the new to the old and grease the wires best you can and pull them through.
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post #7 of 25 (permalink) Old 08-18-2006, 12:15 AM
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Quote:
Originally Posted by Rubline
Can you use the old wires as pull wires for the new stuff? solder the new to the old and grease the wires best you can and pull them through.
Um, we're talking about fishing wires through a hole, not a medical procedure. That kind of sounds like, um, has anyone seen my gerbil?

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post #8 of 25 (permalink) Old 08-18-2006, 10:42 AM Thread Starter
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Wierd intermittant syndrome

Test...

I logged in twice and wrote a huge explanation. Then it disapeared.
If this works...I'll do it one more time.
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post #9 of 25 (permalink) Old 08-18-2006, 10:53 AM Thread Starter
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Wierd intermittant syndrome

Ok here goes again.

1. Yes "when" is the key word. Strong blue electric charge will jump 1/4" when cylinder is firing. Nothing when it isn't.

2. Seafoam - ran 2 tanks w/ additive, plus blew a load of carb cleaner through intake. No change.

3. How did I determine P/U coils? I switched the regular coils front to back and the problem didn't migrate - stayed on rear cyl. Nearby Kawi mechanic suggested p/u coils. Now that I'm faced with a LOT of work, the guess work is over. I need to check resistance on the p/u coils to be sure. The existing coils don't show much wear, so I am a bit suspicious. Unfortunately I don't have a multi meter and am mystified as to how they are used. Need quick lesson and purchase of multimeter. My neighbor has one and may be able to give me a hand.

4. Fishing - it would work...except for 3/8" square grommet that should be seated inside the slot to the alternator. I thought about cutting it down, but then it would allow crud to enter bottom end and create all sorts of havoc. Also - wire harness at end of connection won't fit through the slot either and I'm not inclined to cut and solder all the wires back...seems like a pretty tentative fix - given my talent in soldering.

For now...need to check resistance and if anyone knows of a shortcut to loosen the alternator cover enough to slip a 3/8" grommet inside the slot - without having to remove the whole engine it would be great, but I'm sensing that isn't going to happen.

Anyway thanks for all the responses and I wish I'd have found this forum 3 years ago.

D
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post #10 of 25 (permalink) Old 08-18-2006, 05:40 PM
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Someone elses idea about the solder. You can pull the wires out of the plug/harness, and then put them back in after fishing the wires. No soldering.

As to how it works, each coil is exactly that, a coil. The wheel that they are up against has magnets in it a strategic locations. When the magnets pass the coils, they induce a small electric charge.

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relocated R/R
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