620dark
You can always get it running with time or money.
Hi folks,
As I mentioned in my introduction, I obtained a 1979 Honda cb650 with 8,1xx miles on the clock. It was a little rough as a result of sitting, and there were some electrical gremlins.
I started by rebuilding the carbs - I used the rebuild kits from a '78 cb750, which fit except for the top cover gasket, which I was able to reuse. I also replaced the accelerator pump and bench synced the carbs. I used a mixture of hot water and pine sol to clean the carb bodies with, and that, combined with some thin copper wire strands, cleaned everything up pretty well. Nothing like the color of clean raw aluminum!
I had discovered that the spark units had melted themselves, and both coil packs were cracked. I was getting a spark, but it was a pretty pathetic one. So, upgrade time!
I used this schematic and some GM HEI parts to upgrade:
http://home.comcast.net/~loudgpz/GPZweb/Ignition/CBheiModCavCoil.html
I ended up using coil packs off a mid 90's Saturn, and made custom wires using non-resistor wire, the stock Honda spark plug ends/boots, and the stock Saturn coil pack ends and boots. I cut the plugs off the melted spark units, and wired in the GM HEI ignition modules, heat sinking them and mounting them to some 1/8" aluminum flat stock. Using the stock plugs made it "plug and play." I mounted the Saturn coil packs in roughly the same place as the stock coils, and the tank covers them up just fine. I can fire a spark about 1/2" now, and in a pinch, use the coils as spot welders! ;D
I also had to re-wind the charging system rotor with fresh magnet wire - the resistance of it was less than 2 ohms, and since Voltage = Current x Resistance, at 12.5 volts, the rotor was using more than 6 amps! Sadly, this high current draw fried the regulator/rectifier, but I was able to use one out of an '83 Nighthawk 650sc.
I used the instructions below as a rough guide for rewinding the rotor, but I used Kapton tape instead of epoxy to secure the windings together. Epoxy was making the wire "donut" too big.
http://deuceswild.yuku.com/topic/1603#.T4D67u03dh9
Anyway, I have 12.5 volts at 1500 rpm, and it just goes up when I rev it, so I'm happy for now.
I had all kinds of problems keeping this thing running, but that ended up being due to there being no air filter or air filter cover on the bike. I found a NOS air filter on fleabay, along with some plastic side covers, but I had to make an improvised air filter cover out of cardboard until I can get one ordered. After all that drama, it starts right up and idles happily.
I also shimmed the carb needles ~1mm with some small washers, as this thing was running kind of lean.
That leads into my current problem - the thing won't rev over ~5,000 rpms. She starts popping and spitting and bogging no matter how much throttle I give. She runs great up to 5,000, but then just falls on her face. Any thoughts as to what I should check? I am going to pull the exhaust pipes off and run it open to make sure there's no obstructions in them, but I'm thinking that's kind of a long shot. Suggestions are appreciated!
As I mentioned in my introduction, I obtained a 1979 Honda cb650 with 8,1xx miles on the clock. It was a little rough as a result of sitting, and there were some electrical gremlins.
I started by rebuilding the carbs - I used the rebuild kits from a '78 cb750, which fit except for the top cover gasket, which I was able to reuse. I also replaced the accelerator pump and bench synced the carbs. I used a mixture of hot water and pine sol to clean the carb bodies with, and that, combined with some thin copper wire strands, cleaned everything up pretty well. Nothing like the color of clean raw aluminum!
I had discovered that the spark units had melted themselves, and both coil packs were cracked. I was getting a spark, but it was a pretty pathetic one. So, upgrade time!
I used this schematic and some GM HEI parts to upgrade:
http://home.comcast.net/~loudgpz/GPZweb/Ignition/CBheiModCavCoil.html
I ended up using coil packs off a mid 90's Saturn, and made custom wires using non-resistor wire, the stock Honda spark plug ends/boots, and the stock Saturn coil pack ends and boots. I cut the plugs off the melted spark units, and wired in the GM HEI ignition modules, heat sinking them and mounting them to some 1/8" aluminum flat stock. Using the stock plugs made it "plug and play." I mounted the Saturn coil packs in roughly the same place as the stock coils, and the tank covers them up just fine. I can fire a spark about 1/2" now, and in a pinch, use the coils as spot welders! ;D
I also had to re-wind the charging system rotor with fresh magnet wire - the resistance of it was less than 2 ohms, and since Voltage = Current x Resistance, at 12.5 volts, the rotor was using more than 6 amps! Sadly, this high current draw fried the regulator/rectifier, but I was able to use one out of an '83 Nighthawk 650sc.
I used the instructions below as a rough guide for rewinding the rotor, but I used Kapton tape instead of epoxy to secure the windings together. Epoxy was making the wire "donut" too big.
http://deuceswild.yuku.com/topic/1603#.T4D67u03dh9
Anyway, I have 12.5 volts at 1500 rpm, and it just goes up when I rev it, so I'm happy for now.
I had all kinds of problems keeping this thing running, but that ended up being due to there being no air filter or air filter cover on the bike. I found a NOS air filter on fleabay, along with some plastic side covers, but I had to make an improvised air filter cover out of cardboard until I can get one ordered. After all that drama, it starts right up and idles happily.
I also shimmed the carb needles ~1mm with some small washers, as this thing was running kind of lean.
That leads into my current problem - the thing won't rev over ~5,000 rpms. She starts popping and spitting and bogging no matter how much throttle I give. She runs great up to 5,000, but then just falls on her face. Any thoughts as to what I should check? I am going to pull the exhaust pipes off and run it open to make sure there's no obstructions in them, but I'm thinking that's kind of a long shot. Suggestions are appreciated!