First Gen battery question/carbs

[mark_gober]

Hey everyone,

I've recently rebuilt the carbs on a 1982 Magna that I'm trying to bring back to life.  After removing/reinstalling the carbs three times, I think that I've finally got everything correct.  (at least according to vacuum readings and a steady idle)  I've got a few questions that hopefully everyone can help me out with.

First is the battery.  On cars, you can disconnect the battery and the motor will continue to run (assuming you have a good alternator).  My Magna's battery was dead and so I was using jumper cables to start it.  Once I had the engine idling smooth, I figured I'd take it for a test drive around the block, but as soon as I disconnected the battery cables, the motorcycle died.  Is this normal?  Perhaps this is common knowledge in motorcycle circles, but the last motorcycle I rode was a 125cc dirt bike in 1988. 

My next question is regarding the carbs.  The engine does idle and appears to have exactly the same vacuum on all four carbs.  I did notice two interesting things though.  When I was installing the vacuum gauge (while the engine was running), on two of the cylinders, when I removed the screw to install the vacuum gauge, the engine speed increased.  On the other two, as soon as the screw was removed, the engine abruptly died.  Last night, when I had the engine idling, I took a can of B-12 with the straw and shot a tiny shot of B-12 down the carb throats.  On two of the carbs, the engine speed increased and on the other two, the engine hesitated and almost died.  Since there was about two weeks between my experiments, I'm not sure if the cylinders that increase speed are the same two that increase speed when the screw is removed, but I'd certainly suspect that they do.  Does anyone have any insight into what that might mean? 

Thanks for everyone's help.

Mark

[John Luttrell]

Hey everyone,

I've recently rebuilt the carbs on a 1982 Magna that I'm trying to bring back to life.  After removing/reinstalling the carbs three times, I think that I've finally got everything correct.  (at least according to vacuum readings and a steady idle)  I've got a few questions that hopefully everyone can help me out with.

First is the battery.  On cars, you can disconnect the battery and the motor will continue to run (assuming you have a good alternator).  My Magna's battery was dead and so I was using jumper cables to start it.  Once I had the engine idling smooth, I figured I'd take it for a test drive around the block, but as soon as I disconnected the battery cables, the motorcycle died.  Is this normal?  Perhaps this is common knowledge in motorcycle circles, but the last motorcycle I rode was a 125cc dirt bike in 1988.  

My next question is regarding the carbs.  The engine does idle and appears to have exactly the same vacuum on all four carbs.  I did notice two interesting things though.  When I was installing the vacuum gauge (while the engine was running), on two of the cylinders, when I removed the screw to install the vacuum gauge, the engine speed increased.  On the other two, as soon as the screw was removed, the engine abruptly died.  Last night, when I had the engine idling, I took a can of B-12 with the straw and shot a tiny shot of B-12 down the carb throats.  On two of the carbs, the engine speed increased and on the other two, the engine hesitated and almost died.  Since there was about two weeks between my experiments, I'm not sure if the cylinders that increase speed are the same two that increase speed when the screw is removed, but I'd certainly suspect that they do.  Does anyone have any insight into what that might mean?  

Thanks for everyone's help.

Mark

Mark, the bike should continue to run after disconnecting the jumper cables, I suspect that you have a bad generator or regulator.  As far as the carbs acting differently with the B-12 being sprayed and with the vacuum screws opened; the carbs that increase RPM with a shot of B-12 are probably set leaner than the ones that stumble with a shot of B-12.  You should make sure that the idle mixture screws are adjusted properly; you may even have an out of sync condition and will require resynched.

[mark_gober]

John,

Thanks for the info.  I'm going to go perform a pilot screw adjustment in a moment.  How would I isolate the problem to either the regulator or the alternator? 

Hopefully, it's an alternator.  I've got a spare motor i could pull one from.  If it's the regulator, I'll have to locate one and spend some bucks.

Mark

[dgc67]

If it's the regulator, I'll have to locate one and spend some bucks.

If it is the regulator let me know.  I think I have a spare you can try for the cost of shipping it to you.  I can't say whether or not it works but it is off an 82'.
With the bike running check the battery and see what the voltage is.  Without the jumpers on and the engine running it should be putting out about 14 volts.  The fun part is figuring out how to test it before it dies.  Might be best to start with a fully charged and known GOOD battery.

[Magnum Magna]

I know you have a 1 gen but on a 3 gen if you have a dead battery it will not run unless you are doing about 3500 RPM.  It will run with a very low batter but a dead battery it will not.

Like DG said I would put it on a low charger (2 amp or less) for 3 or 4 hours before doing anything.


Make sure the car is not running when jumping your bike it will mess up the Regelator or stator or both.

[John Luttrell]

I know you have a 1 gen but on a 3 gen if you have a dead battery it will not run unless you are doing about 3500 RPM.  It will run with a very low batter but a dead battery it will not.

Like DG said I would put it on a low charger (2 amp or less) for 3 or 4 hours before doing anything.


Make sure the car is not running when jumping your bike it will mess up the Regelator or stator or both.

Very good point, I forgot that the bike won't charge good until above 3k RPMs and below that the battery is carrying the load.