printjunky
09-02-2011, 10:43 AM
Check this out. Just got dome with a motor out (Cam/buncha other stuff) and back in. Down to the tuning stage. And I have come across quite a little mystery.
I have some kind of short that is energizing the block. A little. As far as I can tell, the block is getting between .14 and .3 volts (yes, less than a volt) at (if I'm reading the scale correctly) about an amp or a little less. I first got a hint that something was wrong when the little throttle turnbuckle between the carb and the throttle lever was a bit hotter than the ambient and engine temperature would indicate. Didn't think anything of it at the time, I was just getting it back running then. But then yesterday, during final tuning, it was doing the same thing. The throttle turnbuckle was getting hot. It does not get extremely hot. I doubt it would burn my hand (or burn much) but I can't hold onto it for very long. But it is obviously a point of just the right amount of resistance for it to heat up. And nothing around it has a similar resistance, apparently, so doesn't get hot. Even the stuff the turnbuckle's connected to. In fact the fact that it's totally isolated to the turnbuckle was the initial mystery - before I discovered the voltage everywhere. And before I discovered this: Slightly more alarmingly than a hot turnbuckle, while I was messing with the timing yesterday, and would overdo it one way or another, when the engine would "back down on itself" - like there's negative-resistance to turning over - as it released, I'd get a pretty good spark from somewhere down by the electric fuel pump (mounted underneath the seat box - I can see the spark because I have the center seat opening out).
So I strapped the meter to ground and tested around. Got the same little voltage just about anywhere on the block that I tested.
I'm not too worried about tracking it down. I'll find it eventually. Just start at one end and unhook until it goes away. But any other tips or tricks are welcome. The weird part is that the short is keyed. Remember I have reversibly grafted in a modern fuse box (see previous posts), so my system's a little different than yours. And I have almost everything on my rig set up as keyed. But I removed EVERY fuse, and still got the keyed voltage. I guess that might help me track it down. Eliminate what it's probably not.
Also, this problem is almost certainly much more recent than my wiring job. I suspect it is related to the recent motor in/out. There's no way, as much as I've tinkered with it, that I would have not noticed the hot turnbuckle. It's obvious as soon as you touch it that something's weird.
I have some kind of short that is energizing the block. A little. As far as I can tell, the block is getting between .14 and .3 volts (yes, less than a volt) at (if I'm reading the scale correctly) about an amp or a little less. I first got a hint that something was wrong when the little throttle turnbuckle between the carb and the throttle lever was a bit hotter than the ambient and engine temperature would indicate. Didn't think anything of it at the time, I was just getting it back running then. But then yesterday, during final tuning, it was doing the same thing. The throttle turnbuckle was getting hot. It does not get extremely hot. I doubt it would burn my hand (or burn much) but I can't hold onto it for very long. But it is obviously a point of just the right amount of resistance for it to heat up. And nothing around it has a similar resistance, apparently, so doesn't get hot. Even the stuff the turnbuckle's connected to. In fact the fact that it's totally isolated to the turnbuckle was the initial mystery - before I discovered the voltage everywhere. And before I discovered this: Slightly more alarmingly than a hot turnbuckle, while I was messing with the timing yesterday, and would overdo it one way or another, when the engine would "back down on itself" - like there's negative-resistance to turning over - as it released, I'd get a pretty good spark from somewhere down by the electric fuel pump (mounted underneath the seat box - I can see the spark because I have the center seat opening out).
So I strapped the meter to ground and tested around. Got the same little voltage just about anywhere on the block that I tested.
I'm not too worried about tracking it down. I'll find it eventually. Just start at one end and unhook until it goes away. But any other tips or tricks are welcome. The weird part is that the short is keyed. Remember I have reversibly grafted in a modern fuse box (see previous posts), so my system's a little different than yours. And I have almost everything on my rig set up as keyed. But I removed EVERY fuse, and still got the keyed voltage. I guess that might help me track it down. Eliminate what it's probably not.
Also, this problem is almost certainly much more recent than my wiring job. I suspect it is related to the recent motor in/out. There's no way, as much as I've tinkered with it, that I would have not noticed the hot turnbuckle. It's obvious as soon as you touch it that something's weird.