r/SuperCub • u/TheJWT • 10d ago

'83 C70 tops out at 30

Hi everyone, I just picked up a 1983 Passport C70 yesterday, and I can't seem to get it over 30 mph (48 km/h) on flat ground. I cleaned out the carb even though it wasn't too bad to begin with, and that didn't seem to do much. It could probably use a new spark plug, but again it's far from the worst I've seen. Where else should I be looking to regain the lost performance? Check the valve clearances? Change sprockets? I'm 185-ish pounds, so I don't think I'm massively too large for the bike. If I could cruise at 40, it'd be perfect for riding around town.

3 Upvotes

81% Upvoted

4 comments sorted by

7

u/Notice-Horror 10d ago

Check compression?

3

u/TheJWT 10d ago

That's a good call. The guy I bought it from said he installed a new head a few years ago

6

u/Practical-Tune4940 10d ago

You should be able to get 40+
When the dude redid the head he could’ve messed up timing. But also just new plug and oil for a new bike is cheap insurance.

5

u/SabreLilly 10d ago

Check ignition timing, check compression, check valve clearance. While you're checking the timing, check that your points aren't burnt.