Another angle on the hot start issue?
Hey everyone- fyi I'm on an '04 VN750 with 42,000 miles. Last year when I bought it I was having the same hot start issue everyone on here complains about. A set of NGK iridium plugs and a MF battery later and presto chango, hot start problem is gone. A year goes by, and suddenly this summer the issue has come back. I pulled the spark plugs and cleaned them up, they seem just fine. I have also done a partial pickup coil mod (when I gapped them to .020 as recommended I got a nasty squealing sound coming from them when I fired up the engine, so I backed it off to about .025, I may revisit the mod later). The pickup coil mod seems to have helped a bit, but hasn't gotten rid of it.
When I was testing out the pickup coil mod, I came across an interesting finding. The bike had zero problems restarting until the PRECISE MOMENT the radiator fan kicked on. Once that happened I had to let the bike sit 15-20 minutes before it would fire up again. So, here's my theory and what I've done about it so far:
I think that the battery is being barely undercharged, and when the radiator kicks on that puts a load demand on the battery that's just slightly higher than the charge rate. This would be a cumulative effect, slowly draining the power every time the radiator came on over the past year, until a couple of weeks ago that it became drained just enough for it to begin affecting restarting again. Alternatively, the charging system is fine but for some reason the radiator is drawing more current than it should be. To test this, I picked up a battery tender and plugged it into the bike today. As soon as I plugged it in I got a red light on the tender unit, indicating the battery was less than 80% charged. 20 minutes later its a blinking green, and an hour after that solid green, indicating full charge.
I then fired up the bike and let it sit until the engine warmed to the point of triggering the radiator fan. Unfortunately recharging the battery wasn't quite enough to eliminate the problem completely (however, it wasn't as bad as before, it hesitated to start but didn't need to sit as long). I pulled the key out of the ignition and plugged the battery tender back in and, lo and behold, the red light is on again. Somehow this battery is getting drained and quickly, and I believe the radiator fan is the culprit. Or maybe I'm talking out my a**
Thoughts, suggestions on where to go from here? To my knowledge there have been no other mods to the stator or regulator/rectifier, but I can't be certain as I am not the original owner. I also have only limited tools and mechanical experience, so I'm hesitant to get too crazy with mods here.
Last edited by bluguitar89; 09-10-2014 at 11:25 PM.