Tuning a Honda Cub 90

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Tuning a Honda Cub 90

...and now for something completely different

It looks like a group of us are going to be doing a charity ride from John O'Groats to Land's End on Honda C90s at the end of August.

Obviously silly thoughts are coming into my head now about tuning a C90 but without spending too much money.

There are 110cc big bore kits but they're over £100 and require the crank case to be machined.

Replacing the exhaust is a possible but it'd be nice if it looked original. Maybe just hack some of the baffles out of a normal one?

I'm guessing that the obvious tweak would be to replace the carb or needle and fit a K&N style filter.

Just sounding this out in case anyone's got any other suggestions (Nitrous isn't an option ).

Looks like there's some suitable tuning parts at Monkey-Bike Direct.

LMAO it does need to be reliable I'm just shaving 2" off the leg shields for a bit more top end

Couch Commando wrote

LMAO it does need to be reliable I'm just shaving 2" off the leg shields for a bit more top end

My mate took the screen off the front of his and was pretty sure that he was getting somewhere near 5mph better top-end out of it.....it was probably just the increased wind noise making him think that he was going faster


Get some nitrous...it'll go loads faster once, for a couple of seconds

modify the air box and jet accordingly... would look amusing on the dyno though!on my first bike, a c50, there was a weird thing going on with the carb/choke... it would top out at indicated 35mph, then if i pulled and pushed the choke knob a few times, it'd accelerate (yes, pull rather than slowly gain...) to 48mph! was funny cos all the kids from 'better off' families had the trendy bikes - rd/dt/ar 50's and i'd whup them on this shitty old c50!how about running it with just one piston ring instead of 2 (not sure which one you'd run with), i've heard it's a mod some people use in racing (though not c90's...)ooop north, where it's said to be grim, i know there are some c90 endurance races organised... might be worth contacting those for some helpful info??? as they do endurance, they have to remain pretty reliable...gotta be some easy zorst mods i'd imagine...

you could modify some hoover tubing and create some form of ram air??

Brilliant - a tuned C90! Please, whatever you do, post all the details of your hot tuning vamps/dyno reports etc.I had one years ago. No, it was not glam but it was fanatastic for the 5am trip to the station in all weathers. I probably filled the tank three times a year - it would run off the steam from my piss.

hang on a minute.....wasnt pegeot or someone producing a blown scooter? Think it was a super rather than turbo-charger. Perhaps you could adapt one of these units onto a c90! gotta be worth a go

I tuned my old C70 by cutting the strange bulbous airbox in half and turning the bit that was still on the carb, the other way round to generate a ram air effect. To compensate for the lack of filter I used an old pair or tights and some tape over the opening.I remember getting an indicated 73mph out of it down Noak Hill Road before valve bounce set in. We used to skim the heads with wet & dry glued to a bit of glass. The ports are quite tiny so maybe a few hours with a Dremel would reap some rewards.

well i dunno if its a good idea but a friend of mine used to run the "house" c90 (pizza boy) on nothing but pro boost ... spost to be a cup full of this stuff to a tak of petrol ... we just used to fill the tank up and splash a bit of petrol in it ...on a long enough road could get an indicated 78mph ... used to spit flames outa the zaust on the over-runit only lasred 1100 miles before it totally melted down and we threw it in the river ...still there we think!oh and we removed all the plastic , all of it , not a bit left yet ...

I did a of C90 stuff a long time ago.I think a CD175 piston was the one to use for an oversize, has the same pin diameter.....but is bigger dia than max oversize.Home made large bore inlet tract from car exhaust...its got to have the correct curve to it to keep the carb level.May have to change to a conventional twistgrip to get enough cable movement if you go for a big carb. Then you have to sort out the handlebar diameter cos the standard C90 is thinner than normal bars.Weight (and drag) can be lost by ditching plastics and trimming down rear mudguard. The complete front end can be swapped for conventional front end off a small moped. This gives better brake, conventional forks, handlebars etc. You could even have a tacho then...one that works off the LT side of the coil. Late 80s KTM 50 was a good one to use cos they had mag wheels as well. Rear wheel fitted easily too But I guess they have all gone now.Cant run them without a battery (strange but C50 & C70 will run OK without)Good luck........maybe modern oil will allow a good bit of tuning without killing the engine..........not sure about the clutch, though

Thanks for the info and support guys.....I'll keep you posted on any progress

Sounds Good, Have a look at the Honda ATC110 and ATC90 tuning parts on the net, you can get big cams, megaphone exhaust, big Mikuni Carb, and Superchargers are also available for these,Supercharger; the linkhttp://www.powerbikeusa.com/powerbike/z50_parts_page.htm Have Fun!Nat

the ign timing is retarded on the C90 to allow the use of cheap Indian fuel. Advancing it by 3 degrees makes a huge difference. This is done by welding an extra blob on the flywheel in addition to the existing blob and dressing it. Luckily 1 degree = 1mm on this one so is easy to do. Also, a race ign CDI is around £20 and removes the limiter as well as altering the ign map.

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