CB550 Help


Been Around the Block
Have a 75 cb550 that wont start, put multimeter across ignition coils and one of them was reading 1 ohm... So I bought a new one, when it came in I made sure to check it before installation. It read 3.6 Ohms prior to installation. Put it in, bike still would not start so I checked them again and the coil I replaced is now reading back at 1 ohm.

Here is the problems known and how I have addressed them thus far:

Previous owner removed stock ignition coil bracket and put in and replaced it with accel super coils under the seat. One was reading 1 ohm so I bought a new super coil kit in hopes it would alleviate the issue of why the bike wouldnt start. New spark plugs, new wires, and new coils. Still no start. Going to make sure timing is set correctly next

Question: On this cb550, where do the ignition coils get power from? as the p.o. ran his own wires. Found them routed to the points. where else?

Another issue is the carbs will have a steady stream of gas out of the drain tubes when the petcock is on. I replaced the floats and needles and seats and adjusted floats to the correct height yet they still will pour gas out.
the original coils are wired as follows:

Both coils are bolted to a pair of aluminum mounts, which they are mounted to the frame under the tank with a ground wire eyelet. This is how the coils get ground. There will be a black wire with white tracer that provides switched 12v to the pair of coils. There will be a yellow wire to connect to one coil, and blue to the other....these route back to the points as the wires that "excite" the coils.

it sounds to me like there is a short in the PO's "custom" coil/wiring botch job and I would look through that to see what's what. you may have burned up the old coil due to this short, then immediately burned up the new one because the issue may never have been the coil itself. I'd remove the new one and test both that and the old coil on the bench and see if either reads closer to the 3ohm mark again. if not they're now both trash.

regarding your leaky carbs.....inspect the brass overflow tubes that are in the bowls.....look for cracks in them as this can happen and give false overflowing even when float height is correct (21mm). Another issue I've found is a lot of aftermarket float needle seats have an inferior o-ring on them....they are too fat to begin with and difficult to get in without the carb body actually cutting the o-ring causing fuel to leak from behind the seat even when the needle valve is closed. Both of these issues can make a man crazy as you try everything under the sun to stop the overflow with zero impact on the leak/result. These are the only two things that would cause overflow unless the float height is incorrect or magically all 4 new float valves and floats are no good or all 4 magically have a spec of dirt in the seats at the same time.
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