QuestionBill,
I have a 1972 CL175 K6 with only 2000 original miles on it. It was my first restoration project. It had been sitting in the basement of Cincinnati’s Union Terminal for several years. Over the span of 3.5 months I got it looking near mint, then I took it into the local cycle shop Autobahn Craftwerks to have the engine tuned up; it had not run in a long time. When I picked it up from service, everyone in the shop kept bragging how awesome the bike was; it ran really strong when I first got it back. At times when I laid into the throttle, I thought it was going to take off and leave me in midair. I rode it around within the city limits very limitedly for a couple weeks never really going much faster than 45mph. I even took my sister for a few short rides and it effortlessly pulled our combined weight of 350lbs. up the steepest hills. Finally one day, I took it out of the city and got to open the throttle up. After riding the bike for a good half hour, it began to intermittently bog down for spans of 30seconds to a minute+ and then it would go back to running well/ normal again for 5mins or so. When it would repeat this acting up, sometimes it would lunge and other times the engine sounded like it was dragging down and the bike would only go slow even when you were holding the throttle wide open. Letting up on the throttle or pulling over for a few seemed to help the bike get through it’s acting up cycle but that would only last for a few seconds. I tried loosening the gas cap and operating the choke when these symptoms began and it seemed to have little to no effect. I’ve blown through the gas cap, the carbs were rebuilt by Autobahn, all new fuel lines and filters were installed. Petcock has been cleaned out. I was told the petcock stem had a hairline crack but should not be a problem but that I should eventually replace it. I had mostly a full tank of gas when the symptoms occurred.
I called the shop again and they took another look at it for me. They had the bike for a few days and they tell me they can’t find anything wrong… I knew this was going to happen. Sure enough, I pick it up and take it for a long high speed ride and the problem still exists. It does not show these symptoms at slow speeds. But as soon as it gets its first gulp of high speeds, wide open throttle, it intermittently boggs down.
Last time I took it out, after riding a few circles around the driveway to warm it up, I was on the bike less than 2minutes before it acted up. I jumped directly onto a 55mph road and openend the throttle up. It bogged down after about 300 yards and I had to pull over. I pushed it back to the house and tried to ride it through the grass, up a small hill. The bike wanted nothing to do with the little hill. I had to turn it off and push it. I thought the bike smelt a bit hot so I opened the dipstick. When I removed the dipstick, I saw steam coming from the oil reservoir. Is this normal? After letting the bike cool, I checked the oil level and it seemed fine.
The bike starts fine and will idle Ok after riding a few circles around the driveway. I feel this bike is so close to being awesome, just can’t seem to figure out this one discouraging issue. Any ideas on where I should start? I keep thinking possibly the exhaust needs cleaned which I’m unsure the best way to go about ? or faulty Spark advancer. Maybe it’s the carbs (high speed main jet) but find it a little hard to believe it’s the carbs since the cycle shop went over them twice. They did say the carbs were shot and took a lot of work. Perhaps a faulty return spring in the carbs is sticking ? Weak ignition coil? I’m just making guesses. Help me sort through this please…
Also, on one of my in the city slow speed cruises. both the tach and speedo quit working when I was climbing a hill and winding the engine out. I thought the bike was going to die for a second, I pulled in the clutch and had to keep it reving, at the same time both the tach and speedo quit working. Any thoughts on this ? Could this be related to my other problem at all?
p.s. (I also have a 1972 CB175 K5 that I could temporarily swap parts off of to test remedy theories. )
AnswerJames... start at the beginning.....
Check compression... should be about 175psi. If you see aluminum deposits on the ends of the spark plugs, then the pistons have been seizing.
Check valve adjustment.. .002" cold intake/exhaust
Check spark advancer function.. advance/retard smoothly.
Verify ignition timing at the F mark with .014" maximum point gap.
Verify that the carburetor slides are not in backwards.. Cutaway goes towards air filters. If you put them in backwards, the plugs will foul and it won't idle properly after it warms up.
If bike has stock air filters and exhaust system, then stock carb jetting settings should be fine.
There are six carburetor calibration settings.. carb bodies are stamped with a code...
CBD, CLC, 306A, 644A, 653A and 306B are the options. Main jet sizes range from 90 to 98. Idle jets could be either #35 or #38. Needle clip positions can either be middle or 4th from the top. Float levels are 21mm for all models, however.
Battery must be fully charged and the charging system maintaining that level of charge at all times, with or without lights on. Check spark plug caps for 5k ohm resistance values, when you unscrew them from the ends of the plug wires. NGK D8HA spark plugs are the standard heat range.
Make sure that the brake light isn't staying ON, as it will run down the battery during lengthy drives. Check all the electrical connections for clean and tight contacts.
Bikes "bog down" due to either running out of fuel, fouling spark plugs, running spark plugs in the wrong heat ranges, fuel flow issues, carburetion calibration problems, incorrect spark timing/advance and piston seizures, due to overheating from any of the above causes. If you put KEYSTER carb kits in the carbs, the calibration may be off.
Bikes that sit for years often have piston seizure issues from moisture condensing inside the cylinders, forming rust and corroding the piston rings into the ring lands of the pistons. When the rings cannot move and expand/contract their ability to maintain compression is compromised. If you are getting a lot of smoke out of the exhaust pipes or the breather tube, then you may be having compression issues.
The tach and speedometer internally greased bushings are all dried out now and the units will often either go wild with big needle swings or stop altogether. Make sure your cables haven't snapped off inside, before testing the meters. The meter issues are not related to engine running problems, as they are mechanically driven, not electrically powered.
Hope this helpful for you.
Bill Silver
