I've rad a lot about the inadequate electrical on the old twins. @40 years old things have no doubt gotten worse over time. The bike runs but i wanted to go through the system and verify proper operation of the components. (Alternator, regulator, etc... ) I have a multimeter and have been trying to read up on proper testing procedures, although most of what i have found relates to modern car electrical systems but i figure most of it translates over.
If there are any special techniques or tips you guys have please let me know.
I also do not know what the factory correct specs for these components are. I will be able to get numbers but I don't know if they really translate into a properly working component or one that is out of spec. If anyone has these specs please post them up. I imagine the GT/S/SS from 74 all have the same components but if I'm incorrect, and model matters this is for a Sport.
Thanks
Dan
'74 Twin electrical testing
Re: '74 Twin electrical testing
Hi Dan,
I just replaced the rotor and the regulator rectifier on my 74 GT750. The performance in terms of charging and reliability is off the charts better than the stock alternator.
I ordered the alternator rotor from these guys
http://www.carmo.nl
An electrex RO93 for about $200 delivered to my door. Simply swap out the old rotor. The magnets on the ro93 are much stronger so they will induce a higher voltage even if you left your stator and regulator rectifier as is.
I also picked up an ADC6000 rectifier/regulator on ebay for $80. I believe Steve on this site has some regulators that will work as well. I was able to source it from Canada so logistically and customs wise it was easier for me to buy it here in Canada
I then modified the alternator stator so that the two coils were in parallel and removed the center tap wire. There is a post on here that details what I did to modify the stator.
If you plan on riding your bike regularly I would recommend the mod, I'm quite pleased with the results.
If you want to measure how well the current system is running you can get a low Ohm (<.1 ) but high wattage resistor and put it in between the positive terminal of the battery and the terminal leads. When the voltage drop over the resistor is 0 then your charging system is meeting the draw the bike is putting on charging system and the entire system is in equilibrium. When the positive lead from your multimeter is on the positive battery terminal and the black(common) is on the other side of the resistor, if the voltage drop over the resistor is negative then the system is charging the battery(the voltage from the regulator less the draw for the bike electrics exceeds the battery voltage). If the voltage drop is positive you have a draw on the battery.
Good luck,
Bernie
I just replaced the rotor and the regulator rectifier on my 74 GT750. The performance in terms of charging and reliability is off the charts better than the stock alternator.
I ordered the alternator rotor from these guys
http://www.carmo.nl
An electrex RO93 for about $200 delivered to my door. Simply swap out the old rotor. The magnets on the ro93 are much stronger so they will induce a higher voltage even if you left your stator and regulator rectifier as is.
I also picked up an ADC6000 rectifier/regulator on ebay for $80. I believe Steve on this site has some regulators that will work as well. I was able to source it from Canada so logistically and customs wise it was easier for me to buy it here in Canada
I then modified the alternator stator so that the two coils were in parallel and removed the center tap wire. There is a post on here that details what I did to modify the stator.
If you plan on riding your bike regularly I would recommend the mod, I'm quite pleased with the results.
If you want to measure how well the current system is running you can get a low Ohm (<.1 ) but high wattage resistor and put it in between the positive terminal of the battery and the terminal leads. When the voltage drop over the resistor is 0 then your charging system is meeting the draw the bike is putting on charging system and the entire system is in equilibrium. When the positive lead from your multimeter is on the positive battery terminal and the black(common) is on the other side of the resistor, if the voltage drop over the resistor is negative then the system is charging the battery(the voltage from the regulator less the draw for the bike electrics exceeds the battery voltage). If the voltage drop is positive you have a draw on the battery.
Good luck,
Bernie
Re: '74 Twin electrical testing
FYI The manufacturer for the regulator is Arrowhead Electrical.