1972 Honda CL70

Hello, new to the forums. This is a 3 down 1972 CL70 that starts right up w 1 or 2 kicks. The guy I bought it from has it hooked up so there is no key, just kick over and runs, shut off w a kill switch he hooked up . Idles great but when going starts to bog down. It ran great for years but when I was going to sell it I showed the potential buyer how to kick down 3 times to change gears etc without using a clutch . He rode it at high rpms for a mile in 1st gear and when he got back I yelled at him wtf dude. Said it was hard to kick down so he didn’t. Omg I was not happy. So that’s when the bogging started. It’s crazy that it still starts so easy. Any ideas as to what happened. I am not experienced w motors. So thank you for listening.

First things I'd check: compression, via the kickstarter (rotate it by hand); point gap; air filter assembly (for any restrictions, including aged foam)carburetor...specifically the emulsion tube wall orifices & fuel height inside the bowl. These are all fairly easy and don't cost anything to inspect...the most logical starting points, too.

I'd suggest also validating your valve/tappet clearances. Over revving a bike usually has pretty abrupt consequences, but this sounds more like something rattled loose or sucked in a little dirt.

BTW, there is no reason to ever, ever, shift one of these without the clutch. It's absolutely murder on the gears and shift dogs.

Unless your CL70's engine or transmission has been changed, your motor should be a 4speed. Either 1down 3up. Or, 4down shift pattern. With a manual clutch.

Do you have a 3speed?? Semi-automatic??

Stock tranny is 4 down

Thank you for all of your responses. The compression is 50 psi. I have read on this forum that it should be above 150psi. Crazy it starts and idles fine. The bike was sold to me w no clutch. Just kick down. I have not ridden it for about a year to see how many gears but I guess it’s 4 down. I started it the other day at my cabin and rode around the yard slowly in 1st gear and shifted to 2nd and it bogged down. I bought it to drive around an Island I live on during the summer. The speed limit is 25mph all over the island so it did fine for 3 years til this knuckleball took it for a ride.

Compression gauge error is distressingly common with small displacement engines. If 50psi as accurate, the engine would be unlikely to so much as issue a random "pop", let alone fire & run. They get weak around 130psi and stop firing around 90.

Do yourself a favor and retest using the "shadetree mechanic's compression tester". Rotate the kickstart lever by hand. If it stops moving when you've reached the compression stroke, the engine is reasonably healthy...at least. At the other extreme, if you have a tough time figuring when the compression stroke has been reached...ruh-roh; time to look inside the intake port, for discoloration. Since you've not said anything about oil smoke in the exhaust, I am assuming that the rings & cylinder walls are okay.

If bike sat for a year how old is the fuel and how did you store the bike? Bogging off idle id be looking into the crab main jet.

My 50 was at 90 pounds- the only way I could start it when cold was to push it. So like racer x says ......

Thank you everyone. Smoke is nonexistent. I will recheck the compression. Gas was filled and a bunch of startron was put in before inside storage. I will also take apart the carb and clean. I do know how to do that.

Also did some research and found out the motor is a 50 cc Honda motor put on the CL70 frame from 1972. The motor is stamped z50 AE. Maybe the guy who sold it to me did tell me he switched it and I forgot. Hence maybe the 3 down shift? I had bought a pristine 1972 CL70 along with it and he gave the “Frankenstein “bike to me for $350 so at the time it was for the island I worked on and did the job I needed it for. I knew the forks were not the originals and the fuel tank leaked a little. I know most people would have been pissed off but it did the job for me and I enjoyed it for 3 years. So no problem w doing a little work on it now. I’m sorry for misposting about the bike.

Also according to the engine number it is a 50cc motor from 69-70 K1. At least I know what I have now. The internet is amazing.

The Z50 and CT70 have virtually the same lower end. There may be some minor differences but, the only ones that matter...functionally...involve the top end. Swap-in a 72cc cylinder/piston, head and carb and you'd have a CT70 3-speed semi auto, with a Z50 serial number. There's a lot of parts interchangeability with all of the 49cc-based motors, including the C90 which was not marketed in the North America. It can get a bit confusing, for this thread. So, I'll conclude the parts interchange sermon with this...the tranny and clutch assemblies can be swapped between any 49cc-based motor. It is possible to build a 3-speed manual or a 4-speed semi auto. The only way to know what your engine consists of is by doing a teardown; it doesn't have to be a complete teardown, BTW.

For now, the biggest question is 49cc or 72cc actual displacement? Using the factory specs, 8.8:1 nominal compression ratio (and that's for the 72cc motors) a Z50 engine should have ~5.5cc combustion chamber volume, with the piston at TDC. Any compression tester fitted with a hose is likely to have more volume than that inside the gauge + hose assembly...and that leads to inaccurate readings. With my gauge setup, a freshly-rebuilt Z50 will top-out around 130-135psig, cranked by hand. Frankly, I don't use a gauge very often. If there's a valve or ring sealing problem, it's obvious to me. Full compression...for practical usage...can be checked well enough by hand-cranking the engine over. 72cc will deliver a sharp spike of resistance; 49cc still fight back just not as hard.

Leaky rings will manifest as oil smoke or/and an oiled spark plug. A leaking intake valve (and it's usually the intake valve that wears out) will manifest as a blackened intake port. Weak compression feel paired with either (or both) of those conditions will quickly tell you where the problem & solution will be found.

Take a close look at the cylinder jug. Displacement markings were part of the original casting detail...LH side, last fin. Pull the intake manifold; 72cc heads, of this era, have a ~22mm port ID. Z50 intake ports are tiny, by comparison.

Thank you racerx! I will forward this to my friend who is helping me.