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Discussion Starter · #1 ·
Just bought a 87 750. Was driving down the road and everything was fine. Then loss of power and loss of my Tach. The bike still ran but with no power or get up and go. Could of my coil went out? would that count for the loss of power and my tach stop working? Thanks for the help?
 

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Loss of the tach often points to a failed pickup coil. I believe it might be the front, but you can look for previous posts, or just see if the front cylinder has no spark. Then test the pickup coil for the dead cylinder.

The pickup coils are behind the round stator cover, these aren't the ignition coils.

The above isn't 100%, it could mean a problem with the front coil wiring or wiring at the pickup coils. So testing needs done.
 

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The 'trigger' signal is missing for the front coil. The coil itself is probably fine. The front pickup is the yellow/black & black pair behind the cover Spockster pointed out. A broken wire there is probably the culprit. Broken wire at the igniter box is another "easy" place to look. Check for continuity on the black wire on the six pin connector between the igniter and the front coil. If all your wires are still connected, it's a bad pickup or a bad igniter box.
 

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Discussion Starter · #4 ·
Loss of the tach often points to a failed pickup coil. I believe it might be the front, but you can look for previous posts, or just see if the front cylinder has no spark. Then test the pickup coil for the dead cylinder.

The pickup coils are behind the round stator cover, these aren't the ignition coils.

The above isn't 100%, it could mean a problem with the front coil wiring or wiring at the pickup coils. So testing needs done.
Both front cylinders are not firing.
 

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Discussion Starter · #5 ·
The 'trigger' signal is missing for the front coil. The coil itself is probably fine. The front pickup is the yellow/black & black pair behind the cover Spockster pointed out. A broken wire there is probably the culprit. Broken wire at the igniter box is another "easy" place to look. Check for continuity on the black wire on the six pin connector between the igniter and the front coil. If all your wires are still connected, it's a bad pickup or a bad igniter box.
I looked and didn't see any broken connection. I know that it is both front cylinders that are not firing.
 

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Assuming you mean both front spark plugs are not firing, that tracks with the suggestions we've made. Use a multimeter to check continuity of all wires between the pickups and the igniter, and the front coil and the igniter. A visual inspection doesn't always reveal the problem. You can probably also check the ohms of the pickup coil itself (unplug it from the igniter first to get an accurate reading). Also check for a short between the wires and the frame. Sometimes the pickup wires get pinched.
 

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Linked a thread with some pics.

The pickup coil with the black wire will be for the front cylinder. The black wire also runs the tach.
 

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Discussion Starter · #9 ·
Assuming you mean both front spark plugs are not firing, that tracks with the suggestions we've made. Use a multimeter to check continuity of all wires between the pickups and the igniter, and the front coil and the igniter. A visual inspection doesn't always reveal the problem. You can probably also check the ohms of the pickup coil itself (unplug it from the igniter first to get an accurate reading). Also check for a short between the wires and the frame. Sometimes the pickup wires get pinched.
Bought a Multimeter today. Put red in red and black in black when I turned the key on it showed 11.6 volts. What would you recommend as my next step?
 

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Did you check the easy stuff like your battery connections and grounds.
 

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Bought a Multimeter today. Put red in red and black in black when I turned the key on it showed 11.6 volts. What would you recommend as my next step?
11.6v means the battery is dead, so it needs charged.

I'd unplug the pickup coils and ohm test the leads. I think you'll find the pickup coil for the front cylinder has a broken wire or the coil itself is shot.

Free download of the repair manual: VN750_Vulcan_Service_Manual_Parts_Catalogue
 

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Discussion Starter · #12 ·
The Black wire from the coil goes into the junction/fuse box and the tach goes into the ingintion box. From both boxes to the end points I have connectivity. How do I test these 2 boxes?
53498
53499
 

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I would guess that the wiring diagram you have is valid for your bike, but the continuity test is giving you unexpected results because all of the wires are plugged in to the boxes. Unplug everything from the igniter box and check again for continuity. There should be continuity from the black wire on the coil to the black wire on the igniter, and there should NOT be continuity from the coil to the black wire on the junction box (which is the starter relay input from the start button).
 

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Slightly off topic, but I felt it was important.

This isn't the cause of the loss of power, or failed tach, but this IS going to cause charging problems. This wire is from your stator to your rectifier. It's corroded and getting hot enough to melt the connector!!!
53502
 

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With key off and run switch off, he ignition coil red wires should have continuity to each other (red front to red rear). It should have no voltage on it, and no continuity with the battery.

Then with key on and run switch on, the red wire should have 12V on it.

Let me double check the other wire on each coil and get back to you.
 

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53503

Here is the ignition system wiring (tach not shown). The BK and G wires both go back to the IC Ignition and not to the junction box. You should unplug that connector to verify continuity.

Also notice the pickup coils. These are under the left side engine cover (won't leak oil beyond a few drops if on center stand). Check continuity from these coils back to the IC Ignitor connector. Better yet, leave that cover on and measure the resistance between pins 8-10 and 7-9 on the IC Ignitor connector (the wire end, not the pins on the Ignitor itself). This will test the wires to the pickup coil as well as the pickup coil itself. 355-535 ohms is the expected range.

53504

Here is the tach wiring. Notice too, there are two wires here that are "BK" but they are NOT the same. There are only so many colors, so they reused some.
 

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Discussion Starter · #18 ·
tested the pick up coils today 475ohms each. tested at the point of connection on IC Box. How do I test the IC Box to see if it is working properly? And what would be your next suggestion on what to test?
 

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You can probably also check the ohms of the pickup coil itself (unplug it from the igniter first to get an accurate reading). Also check for a short between the wires and the frame. Sometimes the pickup wires get pinched.
Unplug everything from the igniter box and check again for continuity. There should be continuity from the black wire on the coil to the black wire on the igniter, and there should NOT be continuity from the coil to the black wire on the junction box (which is the starter relay input from the start button).
 

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Discussion Starter · #20 ·
Update

So far I have tested the
-front coil by hooking it up to the back coil spot
-have tested the wires at the coil and came to 11.6 volts. This is a brand new battery
-Tested the black Tach wire at all Connections
-Tested pick up coils at all connections these came to 475 Ohms
-Tested IC Box it comes to 421 Ohms
 
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