Interesting comments, I agree on the whole that 90+ mph is a bit optimistic! I have a 1970 Honda C90 and my old engine is getting a little weak, having done over 18000 miles. I have however found a place called ooracing that specialises in pit bike engines (i.e c90 copies). They produce a lump called the 160 charger that produces 18bhp on the dyno, it revs to 14000 rpm, has a balanced crank, gas flowed head, big valves, race cam, strengthened valve springs, alloy oil spinner and an oil cooler! I reckon this would propel the old beast to somewhere near the 80-90mph mark. Not sure what to do about the bouncy old suspension though, any ideas anyone?
I think if anybody touched anywhere near 70 mph on a c90, they would have a 90 per cent of losing control, and the front brake on a c90 is reputably atrocious (bad).
These comments about 92 mph speeds are such utter BS that they are detracting from the value of the site here. It was mentioned that a larger sprocket was put on the rear to attain higher speeds... Except when climbing hills that tax your engine's horsepower to the limit, a larger sprocket on the back will result in LOWER speeds. Then again, a much smaller sprocket on the back would probably result in lower speeds with a 70cc or 90cc engine too, because there is no torque to back up such a gear ratio.
I think the only way one of these engines is going to hit 92 mph with any gearing is if the driver was laying prone inside a streamlined torpedo-shaped shell and had miles of run to get up to speed. These type bikes are at their best at 35 to 45 mph. Even 60 mph, while it might be attained down a steep hill, would be hard on the engine and stupid dangerous for the driver.
As for how to prevent headlamp burnouts, I had this problem at the beginning and fixed it by installing a full-wave rectifier between the alternator and the headlamp. This is a simple circuit to build that is just 4 diodes and a capacitor.
The reason the headlights burn out on these bikes is that they are driven straight off the magneto, which is an extremely choppy AC current. Installing a full-wave rectifier smooths out the voltage spikes and provides the headlamp with DC instead of AC current. You will have to separate the headlamp ground from bike ground if you do this because the rectifier output is not ground-relative to the bike. It is not a terribly difficult mod and I have never had the headlight burn out again.
I have a C70 1981, and it does about 47mph in perfect tune when it's possible. I really love all the exaggerations some of the comments record.
A friend of mine had two 1982 C70 Passport motorcycles behind his garage that had been there for 15 years. They were abandoned and left to rust in the endless Seattle rain.
Due to lack of time to restore, he gave them to me. He said he had purchased them with the idea to get them running. There were just enough parts between two of them to get one running bike out of both. One of the bikes had been in wreck and the front forks were bent. It took me eight months of picking away at those endless little restore jobs.
I have been riding the bike several hundred miles now, and the impression so far has been really good. I like running it around 30 MPH where it seems to be most happy. After new tires and fixing a shifting problem due to loose screws, I have lots of hopes to commuting to work on it.
I have restored four motorcycles, and what is it about spiders and filling a bike with their nest? The design of the C70 bike did well to keep the rain out of the electrical components while sitting, not spider proof.
When I got into the wiring, it was clean even after sitting outside in the rain. The seat pan protected the electrical components under the gas tank.
The C70 is an amazing feat of good design, and whoever the designers were, they get a bow from me. The only thing I need to finish the job is the rebound stoppers that go in the front forks.
How do I convert my 1981 Honda C70 6 volt, to 12 volt like the 83 model. Please help me with this, I'm tired of blowing my lamps. Thank you.
I have a 1983 C70 Passport. Right now, with the old, worn out engine (and me weighing 195 with my gear on) I can attain a top speed of just over 55mph. And that is with stock gearing. If a person was inclined too (and crazy enough) you could easily get one to 90+ mph. It is possible for under $600.00, but to do so would render the bike useless around town and for any stop and go environment.
Anyways, I love this bike, I got mine for free out of a friends back yard where it had been sitting for the last 7 years rusting away in South East Alaska. Wonderful bike. Would love another and encourage everyone to ride more!
I bought a 1983 C70 in 1987 for $450.00, rode it for 7 years (until I wiped out in the rain), then sold it for $300.00. I LOVED it! Awesome bike. Did my own maintenance. The only thing I had to replace often was the exhaust pipe because it kept rusting at the joint. It's been 15 years and I still miss it! Now I see one on kijiji for $1000.00!!
I recently purchased a 1981 Honda Passport & am looking to replace its extremely worn out seat. Any leads as to where I can purchase new seat.
You people that claim to get a higher top speed from swapping in a bigger rear sprocket are wrong. You put a bigger front sprocket or smaller rear sprocket for a higher top speed. (although doing so will cut out your starting power) If you ran a 17 tooth front sprocket (instead of the stock 14? tooth) and a 28 tooth rear sprocket (instead of the stock 35 tooth) you could, once you got the bike moving, get up to about 70ish on a flat with no headwind. But the moment you came across any resistance (i.e. headwind, hill) your speed would drop dramatically.
HI! I LOVE THIS CRUISER BIKE. It is the BADDEST and RADDIST around town!!! I was humbly fortunate to stumble across it down south in the RED NECK RIVIERA :)
The electric start is not working and the lights have "issues", guess that a common deal with these things?! I believe it to be an easy fix. However, it kicks over first start and purrs like a kitten. The shifting was a bit tricky at first, so I do not suggest learning to ride on US1!!! Now I have things under control and it's a fun beach ride.
Anyone out there have a reliable hatchback or station wagon or VW bus for equal trade??? Will put pics when I figure out how!