Captain Dave
CB750 Member
Hi all I am a new member and this is my first post. I purchased a non-running 1980 CB750C. Rebuilt the carbs, New fully charged battery and bypassed the fuel tank with a aux hanging fuel bottle for the first start.
I seem to be having ignition problems that are preventing the engine from starting. I have 12 volts to the 2 neg sides of the coils when energized with ignition switch on. I tried to check the static timing.
I disconnected the yellow positive side of one of the coils, hoked up a test light with a 3 way pigtail to that coil connector, reconnected the yellow lead to the pigtail, the 3rd line to my test light and grounded the test light. When I rotate the crankshaft the test light remains on through 360 degrees. Same thing with the blue side of the other coil.
I did a visual inspection of the coils and one of the coils has 2 large cracks. I removed the coils and tested them. They both have a resistance of 480. Manual states 530 +-50 so that seems to be at the limit but passed. I have ordered 2 new coils due to the cracks.
I then removed each ignition wire and checked the resistance through them. #1 5.06, #2 5.43, #3 zero and #4 5.14 all on 200K scale. Obviously # 3 is shot for some reason. I dissembled the plug caps from the wires. The # 1 & 4 have resistors in their perspective caps. The # 2 & 3 do not appear to have resistors? This seems odd but they look original. 2 & 3 are Nichiwa SDO5F 1 & 4 are Nichiwi XDO5F.
I say the # 2 & 3 caps don't have resistors because there isn't a slot for a straight blade screw driver to remove the resistors like there is on the # 1 & 4. This is puzzling any help is much appreciated.
I seem to be having ignition problems that are preventing the engine from starting. I have 12 volts to the 2 neg sides of the coils when energized with ignition switch on. I tried to check the static timing.
I disconnected the yellow positive side of one of the coils, hoked up a test light with a 3 way pigtail to that coil connector, reconnected the yellow lead to the pigtail, the 3rd line to my test light and grounded the test light. When I rotate the crankshaft the test light remains on through 360 degrees. Same thing with the blue side of the other coil.
I did a visual inspection of the coils and one of the coils has 2 large cracks. I removed the coils and tested them. They both have a resistance of 480. Manual states 530 +-50 so that seems to be at the limit but passed. I have ordered 2 new coils due to the cracks.
I then removed each ignition wire and checked the resistance through them. #1 5.06, #2 5.43, #3 zero and #4 5.14 all on 200K scale. Obviously # 3 is shot for some reason. I dissembled the plug caps from the wires. The # 1 & 4 have resistors in their perspective caps. The # 2 & 3 do not appear to have resistors? This seems odd but they look original. 2 & 3 are Nichiwa SDO5F 1 & 4 are Nichiwi XDO5F.
I say the # 2 & 3 caps don't have resistors because there isn't a slot for a straight blade screw driver to remove the resistors like there is on the # 1 & 4. This is puzzling any help is much appreciated.