Just wondering if you might have any ideas for my CG as it’s a bit funny… when starting with the electric start, it sounds funny, kind of like the sound you get if you disconnect the spark plug and try to start it… you can hear the starter motor going but the engine isn’t kicking into action. it sounds like a plunger going up and down or something - it’s hard to describe. It takes a few more goes to get it running (4-6?).
When running, it sounds a lot louder like a BAP BAP BAP sound rather than the normally timid and quiet engine that it is.
I’ve adjusted the valves just to rule that out, and tightened up the nuts where the exhaust goes into the cylinder. Neither have helped. The bit where the exhaust connects to the cylinder seems rather rusty but the rest of the pipe looks fine with only surface rust.
Could it be the exhaust pipe? Would a hole in that rusty bit be causing this? (Is this what they call “low compression”?)
I had an exhaust gasket go on a cg125 engine, sounded pretty similar to your description. It’s literally a piece of metal sandwiched between the exhaust manifold and the pipe to make a tight seal; I made a new out of the bottom of a drinks can and that lasted 9000 miles just fine.
I had an exhaust gasket go on a cg125 engine, sounded pretty similar to your description. It's literally a piece of metal sandwiched between the exhaust manifold and the pipe to make a tight seal; I made a new out of the bottom of a drinks can and that lasted 9000 miles just fine.
whereisgibson
I just googled the exhaust gasket, and yes I remember changing something similar on my previous CG about 5 years ago. I’m guessing if I take the exhaust I will need a new piece of metal (or gasket) to squash? Might be best to get hold of one! Part ordered - will arrive tomorrow!
Did the valves need adjusting? And does it spend longer turning over before starting now?
It sounds like the exhaust gasket’s gone, but you might have other issues, too; has anything happened to the bike recently?
Big Red S
The valves were adjusted 2,000 miles ago, but I did them again last week just to be on the safe side. They weren't in great need of adjustment when I opened it up last week.
It does indeed spend longer turning over. Nothing has happened to the bike recently. Definitely not engine wise. It’s due an oil change, but that’s about it.
A knackered exhaust gasket’s likely to make it noisier, but wouldn’t affect starting. Maladjusted valves would make it harder to start (if the valve’s been adjusted too tight and so you’ve no compression, or too loose and so you don’t pass the gases properly) but probably wouldn’t really affect the noise.
I’d re-check the valve spacings at least, and probably make sure they’re actually all operating properly.
Actually, a leak between the carb rubber and the head would do both at the same time. You’d get a poor mixture (because of the fresh air coming in) and more noise coming out. Not sure how noticeable the noise difference would be, though.
Place a rag over exhsust outlet (silencer) to try block the outlet with engine running … if note gets more prounounced then its leaking exhaust … if engine tries to stall you have a good seal on the system
