I like the VN750, I really do. That is the reason I'm so eager to solve this problem instead of throwing back the bike to the dealer without blinking.

I bought a 92' VN750 last november and I was happy about it for a week...when it refused to start. I've called the dealer, they came and picked up the bike and "worked" on it for 4 weeks and I got it back with the comment "the start engine been replaced". Fine. It was fine for 20 mins cause when I had a short stop at a friend and tried to start again nothing happened. Another call, another pick up and another 4 weeks later they gave back the bike with the comment "we changed the regulator". Fine!
Well....the bike was sleeping in my garage for 4 weeks when I tried to start it refused as before. At that point I got fed up with the dealer so I decided that I have to find what can be the problem.
First guess ofc the battery, I've got a battery charger and after 13 hours the bike was spinning like it was supposed to be. Btw when I bought the bike they said that the battery was "replaced" by a new one which was big time bs.
So I started the bike 2 times in a 2 weeks period and it ended up dead.
I bought a volt meter that I mounted on the bike and it showed only 1 green dot when I was riding the bike which supposed to be not so good. Battery died once again. I bought a new battery yesterday and a multimeter. I decided to go to the deep of the problem. Battery charged, bike started perfectly, idle voltage readings on the battery were 14-14.4V but when I checked between the headlight + and the battery - it was reading 13.5V.
The tricky part comes now....when I spin up the rpm the voltage drops.
It was a bit hard to do it alone to keep the 2 pins of the multimeter at place and fix higher rpm but my guess was that around 4000rpm I had 12.5V. I'm not an uber mechanic but so much I know that this is not good.

Anyone got a wild guess what could that be? Since I didnt have a big enough screwdrived to take off the left hand cover to check a 6 pin connector as the service manual says I have to postprone this action for tomorrow but meanwhile I would like to hear any advice or comment on this, please.

Worse case scenario gonna be a bike through the dealership's window but I try to avoid it cause the bike is quite heavy. :D

hummm.... sounds like the stator maybe? how many miles on the bike? its unusual that the volts drop like that as speed increases....where did u have ur volt meter plugged in at?

26920 miles on the bike but it wasnt used in the last 2 years at all. Volt meter is connected to the headlight's ground wire and red/yellow (if I remember the colour correct) wire.
And there it shows 1 green dot most of the time. Some times 2nd green dot blinking up for a sec when it's on idle and some times even the 1 green dot fades out when increasing the rpm.

If the bike sat for that long, you might want to do like a lot of us have had to do. Disconnect, clean, and reconect every connector on the bike. Some times gremlins are hard to catch.

try cleaning the ground near the battery box, clean all connectors and use dielectric grease on them

good luck, Stan

I did a new test today. The results has been different (dunno why) however the interesting part: less charging with hihgher rpm still stands.
I've got idle 14-14.3V and 5000rpm 13.9V. I was checking the before and after V of the battery and it was actually more V in it than before started so it must have charged it at least.
I've sent an email to the dealer what they think about the higher rpm less charge.
Checking the connections could be a good idea...I'll try to do it this weekend. Even if it not helps cant hurt. :)

... Since I didnt have a big enough screwdrived to take off the left hand cover to check a 6 pin connector as the service manual says I have to postprone this action for tomorrow but meanwhile I would like to hear any advice or comment on this, please...

You may not need a big screwdriver. Use your ignition key to loosen the screws in the side covers. That's why the screw slots are as large as they are, to accept the side or the end of the key as a screwdriver. You may need to use some other tool to help turn the key. I use a small cresent to help turn the key on the "sticky" ones.

CD in Frederick, OK

Well I did the ride to the work on my bike yesterday, totally 40 miles riding. I've checked how many volts in the battery before and after 12.8V/13.0V so looks like after all the charging is ok. My wild guess after what Stan said the contacts that can be behind the first not so good results cause since I removed the 6 pin connector to check the resitant and re-connected it the charging gained that lvl there it supposed to be.
I think I've found out why I get only 1 green dot on the volt meter, too so that should be solved this weekend when I'll relocate the wire of the meter.
However the interesting question remains: How can I have higher charge at idle than at high rpm. Actually I get results at high rpm that supposed to be at idle while the one I get at idle supposed to be at high rpm.
Dealer didnt reply my email yet so I might pay a visit to them after all with this question.
Thanks for the advice and help, I've got lots of ideas from here!

Update: I've moved the volt meter's red wire from the headlight to the brown wire as I saw in a post on this forum before. Looks like it works perfect now. 2 green dots in idle. I've still not got any answer from the dealer about the idle > high rpm charge so this question is still open. Wouldnt be surprised on an answer like "But it at least charge after all isnt it?".

Did you ever get an answer as to why the volts drop as the RPMs increase?

I'm considering buying a 1992 VN750 from a friend. He suspected an electrical problem, so I did some testing.

Starting the bike (cold), I read 14.63 volts at 1500 RPM at the battery terminals. Increasing the engine to 4000 RPM gives me a reading of 14.18 volts. Everything I've read indicates the volts are supposed to go up (but not over 14.8 volts). After riding the bike for a half-hour, I get a reading of 12.42 volts at idle. Increasing the warm engine to 4000 RPM drops the volts a little to 12.39. What gives?

The stator or regulator isn't working on your friends bike :(

See https://www.electrosport.com/Images/fault_finding.pdf

Did you ever get an answer as to why the volts drop as the RPMs increase?

I'm considering buying a 1992 VN750 from a friend. He suspected an electrical problem, so I did some testing.

Starting the bike (cold), I read 14.63 volts at 1500 RPM at the battery terminals. Increasing the engine to 4000 RPM gives me a reading of 14.18 volts. Everything I've read indicates the volts are supposed to go up (but not over 14.8 volts). After riding the bike for a half-hour, I get a reading of 12.42 volts at idle. Increasing the warm engine to 4000 RPM drops the volts a little to 12.39. What gives?