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1986 VN750
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163 Posts
Discussion Starter #1
Ok I've been having problems with my VN750 for 2 years and am hell bent to get it working correctly.

I have a newer battery all charged up, ready to fire it up for the first time in the nice weather and it cranked about 15 times and the battery died. Needless to say Im annoyed w the battery back on the charger.

1- should the battery be dying so damn fast when it's cranking?
2- Would a bad parasitic drain make this happen as soon as I turn the key and suck juice from the starting amperage?
3- How do I properly test for a parasitic drain? I hooked my meter up in series on the negative terminal set to 10 amps and it started smoking pretty much right away. Now im no fool when it comes to multimeters but obviously something isnt right.

The original issue is that the bike would usually start fine and ride where I want to go but once i get there and try to start it again, the battery would be dead. This is intermittent of course. The low beam usually goes on and off at will also. I'm at such a loss as to whereto start.
 

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1986 VN750
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163 Posts
Discussion Starter #2
test results

So I charged up the battery and tested the amperage with the bike off, key out. I got about 107 mili amps. When I pull the main fuse, the amperage drops to about 45 mili amps. I pulled the headlight and tail fuses out as well just to make sure theres no change and the isn't. Only the main fuse changes the amp draw. Should there be any draw at all with the bike off, key out? It's a 1986 VN750 with absolutely NOTHING extra hooked up to it
 

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Super Moderator
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11,958 Posts
Sounds like a bad battery. Is it a wet cell or an AGM battery?

AGM batteries are highly reccomended here...

15 times trying to start the bike sounds like a lot. You might also want to check the charging system.

Go over your ground connections and terminal connections. Then your wires under the seat and the headlight bucket. Look for worn insulation on the wire harness coming out from the front of the tank.
 

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1986 VN750
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163 Posts
Discussion Starter #4
The battery is ok. Had it load tested and was inside charged all winter. Ive gone over all the connections and grounds etc. I think it just cranked that many times because it was sitting all winter. I put the battery back in after charging and it literally fired up on the first crank. My issue here now is, why is the low beam off (comes on occassionally) and why is the battery dead after riding and parked for a few hours.
 

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Super Moderator
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11,958 Posts
Again, check your charging system. Start the bike and measure the voltage at the battery. You should be seeing 12.8 volts or so with the bike off and 13.4 and above with the motor running.
Intermittent headlight can be a sign of a bad stator.

The only way I know to check for a parasitic drain it to disconnect the battery and test for resistance on the two battery leads. You should get no reading from 1 to infinity....
 

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FREEBIRDS MC CENTRAL NY
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16,222 Posts
Yup Yup.check r&r and stator
 

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1986 VN750
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163 Posts
Discussion Starter #7
The stator seems fine. Charges at about 13.8 and higher when at higher RPM's also no ground or shorts between the 3 leads. Still haven't found a good way to test the rectifier yet. Any advice for that?
 

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FREEBIRDS MC CENTRAL NY
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16,222 Posts

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FREEBIRDS MC CENTRAL NY
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16,222 Posts

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1986 VN750
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163 Posts
Discussion Starter #10
I did the blue wire mod and the headlight still does not work. Im thinking maybe theres an issue with the headlight switch or the bulb. Also I found yesterday that I get 140 miliamps at the battery with the bike off and key out. When I pull the main fuse, the draw drops to 45 miliamps. This amperage stays even w all fuses out. Should there be this much draw with the bike off etc? Can someone suggest what/ If any amperage should be present with the bike off, key out?
 

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1986 VN750
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163 Posts
Discussion Starter #11
Also is there any way to get at the ignition without removing the forks?
 

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Super Moderator
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2,570 Posts
yea, you can remove it by turning to the left.. up underneath is a couple screws or bolts.. remove them, and it will drop right out. the key may need to be in a certain position, but not sure of that (I dont remember when I pulled mine if I had to move key or not)
 

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Can someone suggest what/ If any amperage should be present with the bike off, key out?

The fan relay is the only thing supposed to be hooked up outside of the control of the ignition switch. The fan relay primary is connected from B+ to the fan-switch which interrupts the circuit to ground unless sufficient temperature closes it.

During ambient temperatures, though, no current should be present with the bike off, key out.

Is there any corrosion in the junction box area? among the plugs/connectors? any foreign material found its way into the R/R connector? Notice any chafing of the frame paint from the seat through the harness?

Cutting the debugging in half: with all of the fuses back in their places, disconnect the speedometer, tach, dash lamps, etc. basically everything from the neck up from the harness ( all the connectors behind the head-lamp ). What is your drain then?
 

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Still haven't found a good way to test the rectifier yet. Any advice for that?
The test used to be posted here, but it's also in the repair manual, link for download is here too.

Can also try unplugging the r/r and watch the current draw.

A bad r/r can draw current.
 

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FREEBIRDS MC CENTRAL NY
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FREEBIRDS MC CENTRAL NY
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He did the rectifier later
 

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1986 VN750
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163 Posts
Discussion Starter #18
Awesome responses! My post kinda went here and there so sorry about that. Ive done all the charging system troubleshooting previously and found no real issues w the stator. I'm thinking the issue is soley based on the parasitic draw and/or bad R/R. The above comments will be super helpful with finding that draw. I didnt realize a bad R/R would cause the draw. I'll dig into the harness this weekend and report back. Again, thanks for all the great tips. This bike would not have made it this far without this site..
 

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FREEBIRDS MC CENTRAL NY
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16,222 Posts
R&r can do it.mine likes to eat them
 

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1986 VN750
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163 Posts
Discussion Starter #20
Looks like a bad r/r to me!!

So I got her charged up and did some testing. I definitely get an increase in voltage with higher RPM but it only gets to about 13.85 V max. Idling at about 12V.

I'm getting a draw with the bike off and key out of about 80-100 miliamps. Unplugged the r/r and guess what?! the draw is almost gone. I did the testing outlined in the Kaw manual, testing each terminal on the r/r for resistance against the others and every combination failed according to what the book said. Also, looking at the r/r after cleaning the bike thoroughly, it looks like the stock 1986 r/r.. Wow.. So... I know there's a lot on here about Mosfets etc, but what is currently the best place to get a kit? I intend to relocate it under the side fender and bypass the harness.
 
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