22nd Apr 2006, 09:30

79mph eh? What, did you manage to somehow fit a 250cc motor into the frame?

First off, the speedo only goes to 55mph on 80-81s and only 50mph on 82-83s. Second, a carburetor from a 125 is way too big for a 72cc motor. You might be able to start it, but tuning would prove to be quite a chore. Third, at 79mph, the rpms would probably cause the stock clutch to explode and the tires to shred.

I think you meant 79 kilometers per hour.

Never seen people blow so much smoke when it comes to these litle bikes.

Oh, for the record, I have a 110cc Honda Nice motor installed in my 82' Passport. It will bury the needle on my 50mph speedometer. On a good day (warm weather, flat road, tailwind) it will probably hit 65mph. That's with an open exhaust and a 22mm carburetor.

Now, that's not smoke.

21st Sep 2006, 08:23

Actually my Honda C-70 does not have a clutch. The 125 Carburettor bolted up good with a new throttle body assembly installed and spacers.

22nd Sep 2006, 15:09

The C70 does have a clutch. The clutch is designed so it works using centrifugal force. As the engine spins and reaches a certain RPM, the clutch will engage, thus driving the transmission. The design of the clutch removes any interaction between the rider and the system. The setup is similar to a conventional manual motorcycle clutch, but uses more parts and appears rather complex in design and in operation. I would have thought, if one of these clutches decided to explode as one of the comments correctly suggests, the amount of damage would be catastrophic. Be careful.

13th Dec 2006, 11:55

Yes, it is referred to as a semi-automatic, centrifugal clutch. It does require shifting, but no clutch lever action.

Honda did however make this same motor with a manual clutch. They could be found in the models CT70H, XL70, SL70, CL70, SS50, CD50 and a few others.

Now if you're really creative you CAN make your C70 a manual clutch by swapping the parts from one of the above mentioned bikes. You can keep it looking almost completely stock too. You just need to do a little cutting on the leg shield. Oh and you'll need to source a left handlebar switch/parking brake lever from a European C50LAC (which has a FULLY automatic motor)!

See here:


22nd Feb 2007, 16:26

My 1980 C70 is no longer a C70. I have dropped in a lump and gearbox from a 1989 C90. I then transferred the carburettor from a 1986 CB125, have fitted bigger sprocket/wide chain. I had to upgrade the front brake to solid disc set up for safety due to the slightly extra power. Coupled with a total cost of 600 pounds including buying the bike, it is a bargain. It still returns 80Mpg. I think the Cone Air Filter helps.

Right now I am having problems with an initial flat spot, and a missing idle when cold. I have had 92mph out of it on a long hill, not reccomended for more than 5 seconds because it wobbles a lot on the thin wheels at this speed. I am thinking of removing the rear shock and hard tailing it to remedy this. Anyone ever hardtailed one of these?

23rd Feb 2007, 13:56

Interesting comment, I own a 1988 C90, I have not Hard Tailed it, but I did inherit a KMX 125 that my brother had crashed. My father managed to weld on the muffler for me. It sounded very loud, but would stall unless throttle kept two thirds open, even when warm. It was a real babe magnet in my senior school year, by the way it sounded though, I told everyone I had dropped a 250cc motor in the frame.

26th Feb 2007, 21:23

A C90 Scooter with a KMX Kwaka Tailpipe, that must have sounded nuts! No wonder it bogged down so much, funny.

15th Mar 2007, 10:04

I am not sure with all the 70+ miles per hour speeds spoken so highly of on here. I think I would crap myself...

But I have got about to 55ish.

I paid two hundred for the bike with title, and

spent 119 for a new roller bearing cam and 88cc upgrade for the engine.

Put a new 15 tooth front sprocket on the bike.

And changed to a #90 main jet cause of the increase in engine size - it was running a little lean.

It's my around town cruiser, and I can keep up almost everywhere, including the 45mph zones. It works well.

18th Mar 2007, 21:21

Yes friend, going above 70 MPH on a C90 is very very scary, because of the thin wheels and wobbly suspension.

25th Mar 2007, 11:15

Hi there, just bought another 1992 Honda C90 semi auto, great bike and nippy too. I'm having problems with the gears though, when I'm near top end in 3rd gear, it seems to slip into 1st or N. Has anybody got any advice, and what oil are people putting in theres? 10w-40? Thanks.

30th Jun 2007, 15:30

I have a 1982 70 passport, and would like to find a owners manual for it.

14th Jul 2007, 11:48

You can find useful info here: http://autos.groups.yahoo.com/group/Honda-C70/files/ including the user manual and the shop manual.

15th Jul 2007, 08:29

Well where to start? I have an old 1975 C70, and its died soo many times. I am now getting in touch with a guy in the trade, and he has a nice little 125 tumpster engine to go in her (it's a honda based pit bike engine) with all the carb and the lot for the manual upgrades.

I was reading your threads, and it looks like I may need some new brakes. What is the best to use, and will I need to get a wider back tire, coz it looks like it could wobble a bit at say 100. I have a lot of mechanical knowledge, but coming to customizing I ain't got much of a chance!!

Any help well needed.

3rd Sep 2007, 14:53

There is a new 13.9 hp 140cc race tuned engine that just bolts onto the trail models for 425 bucks.

10th Sep 2007, 19:26

I don't see what's so great about going fast; it's dangerous first off. It's more fun to have a responsive smooth riding refined bike that can corner. Sure if I had good money I could throw on a twin turbocharged Hayabusa monster motor, but making it refined as a Hayabusa takes skill and work.

26th Dec 2007, 15:34

Can anyone help please! I need a new headlight for my 1981 C70 - and second, does anyone how to wire the headlight (maybe a resister) to prevent future burnouts?

9th Jan 2008, 08:04

Hi, this is going back to a much earlier comment about someone's C70 being capable of 92mph. That is extremely optimistic. I have an 80cc derbi engined road racing machine. This is tuned as much as possible at 26bhp. This gets it to a true 98mph. The Honda C70 is 10kg lighter, but poorer aerodynamics. I think you'd need about 18bhp to get a C70 to 92mph. That is about three times the power of the standard C70.

One of Honda's greatest 4 stroke 50cc race bikes, the RC116 was only capable of just over 100mph. I have a C70 and a C90 that I use for off roading. I've had about 45mph out of the C70 and 50mph out of the 90. There is no way you could approach 92mph, even on the 90, without masses more power and ridiculous sprockets.

The power would need to be achieved by: much higher compression, serious porting, bigger valves, better cam, oil cooler, bigger carb, programmable ignition and a supercharger. You would also need to run the engine on methanol or nitro fuel. As far as I can see that is really unlikely.

Sorry to moan, but comments like that benefit nobody.

For people who are interested, this chap has a very fast engine that is almost the same to a Honda C50/70. It is a beautiful bike and very interesting. Thanks.