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Discussion Starter #1
Hi folks,

Over the last 3-4 months I've developed a passion for vintage bikes. Just completed the restoration of a 1974 CT 70 and picked up a 1972 CB 175 today!
This actually started out as my son's hobby and I've gotten involved because its a great way to stay connected with my 14 y.o son.

We broke into the '72 tonight. Previous owner said it would idle and rev but bog out at higher speeds. My son is an excellent mechanic for his age and got the
bike running and idling and reving well with no bog. The test drive wasn't impressive thought. With a rider the bike had no power and would only do about 30.
The left side plug was so tight that we could hardly break it lose. Once we got it out we determined there is no spark. There was an intermittent spark with the cap removed from the ignition wire.

Tomorrow's another day. We realize it's going to take time and money but we'll get it figured out.

Looking forward to getting involved and learning on these forums.
 

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1971 SL350 K1
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173 Posts
Old points gave me trouble. It's been a long time since I've used them. When things weren't quite right I left the plug boots loose when I warmed up the motor. Probably retarded the timing a little bit and made it run better. I was learning about points back then. With new good quality points and condensers, properly gapped and timed with good plugs if compression is also good they are a very dependable setup. I've had them last for several years with only minor maintenance on occasion. Check everything and be sure it's up to spec and make sure you have good fuel delivery. If it isn't getting fuel it can't make
power. They are a good thing for a young mechanic to learn about. He will learn something not many younger people know about. Also he will need to do some thinking. The computer diagnostics won't analyze these old systems.
 

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Sensei
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27,163 Posts
BOTH plug wires must connect to a common (usually ground) in order for EITHER or BOTH plugs to spark.....
IF one plug is sparking the other plug wire IS achieving the common ground connection .......
This fault may be occurring anywhere between the coil and the spark gap, including an internally cracked sparkplug.....
Check the "dead" side for insulation cracks, loose connections, bad plug cap and/or bad sparkplug......
You may phone to discuss......
 

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Discussion Starter #7
As an update, the coil on the bike was shot. Installed new one and both cylinders are sparking. Still haven't figured out the fuel issues that are making the bike gutless and only able to achieve about 25-30 mph. Been trying different throttle needle heights.
 

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As an update, the coil on the bike was shot. Installed new one and both cylinders are sparking. Still haven't figured out the fuel issues that are making the bike gutless and only able to achieve about 25-30 mph. Been trying different throttle needle heights.
Is the spark advancer working correctly? Not sure but heard that can affect things
 
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