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Tuning my honda c70

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Pussy Magnet
Scooby Slapper



Joined: 20 Oct 2009
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PostPosted: 16:45 - 20 Oct 2009    Post subject: Tuning my honda c70 Reply with quote

hi , just to add im only 15 , last week i picked up a old honda c70 just for a feild bike its got a new carb and k&n airfilter so far ive been told that a honda c90 cylinder head will go on a honda c70 engine is this true or if it is how much extra power would their be ?

also to add i know the original honda c70 exhuast is restricted so is their any way i could derestrict the exhauast or is their any way i could custom make one to make it better peformance wise .....

i have had a range of feild bikes and that

ktm 250
yamaha dt125
ke100
gp100
mx50 so im not just your average teen lol

cheers peeps
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garth
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Joined: 15 Dec 2004
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PostPosted: 18:57 - 20 Oct 2009    Post subject: Reply with quote

Hi

Mis informed about the cylinder head. The C70 head goes on some of the 90s to boost the compression ratio, not vice versa.

You could try a different cam. Check out all the tuning stuff for monkeybikes.

Or do what I did and put a 110 pit bike engine in it, good for an indicated 55 on the flat. Thumbs Up
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stinkwheel
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PostPosted: 19:02 - 20 Oct 2009    Post subject: Reply with quote

The C70 cylinder head has bigger valves and a hotter cam than the C90 one. You are in posession of the "Holy grail" of Honda Cub cylinder heads. If one were to want to "tune" a C90, fitting a C70 head would be a good first step.

As I recall, a C90 barrel and piston ought to fit.

Oddly, the sky's the limit with tuning that particular engine. Depends how much work you want to put in and how much money you have. The basic engine is the same as they use in (proper) monkey bikes so there is a large aftermarket spares/accessories availability.

The 110cc conversion is popular (you need to TOTALLY strip the engine so the crankcases can be machined out bigger to take the larger barrel). You can have race cranks, hotter cams, nitrous kits, DOHC cylinder heads. You name it, it's out there. They can be made to do in excess of 100mph if you have the funds and expertise.

My two suggestions are not to do with tuning though. If it's for a field bike, look into fitting an MTX125 front end and check the frame has been welded up where it joins the rear mudguard (under the back edge of the seat, look up under the mudguard with a torch). May already have been done, but they can break in half otherwise when abused (it's just pressed together as standard).
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Pussy Magnet
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PostPosted: 07:31 - 21 Oct 2009    Post subject: Reply with quote

Thanks for all your help people Very Happy

but has anyone got any other cheapish ideas i could do to make the bike a bit faster on accleration ?
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Cigaro
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PostPosted: 07:49 - 21 Oct 2009    Post subject: Reply with quote

I would start with a less restrictive air filter and exhaust and tweak the mixture a bit.

C70 is a fun bike - have you thought about road-registering it?
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Pussy Magnet
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Joined: 20 Oct 2009
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PostPosted: 08:18 - 21 Oct 2009    Post subject: Reply with quote

Nah sadly i think its past its time on the road .
what would i need to make it road legel ?
becuase im not to sure about that , someone told me i need to have the leg guards and everything is this true ?

cheers
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Cigaro
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Joined: 28 Mar 2007
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PostPosted: 08:24 - 21 Oct 2009    Post subject: Reply with quote

Nah, you don't need the leg guards.

Really all you need is lights, indicators, and working brakes.

You might also need a mudguard and a chain guard but I'm not 100% on that.

Has it got a number plate and a logbook? If so just get it MOT'd and insured (obviously you'll need to wait till you're 17 because it's a 70).

have fun.

Noticed you said you already had a K&N on it, I'd take the can off and make some form of straightpipe for it, and then as I said tune the carb a bit.
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Pussy Magnet
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Joined: 20 Oct 2009
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PostPosted: 08:31 - 21 Oct 2009    Post subject: Reply with quote

Cheers for that mate Smile will do that get some better tyres aswell .
owww and aswell ive got a bit of plumbing pipe on it now about 15cm long just coming straight off the carb and down il see if that makes a difference in power.
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Cigaro
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PostPosted: 10:13 - 21 Oct 2009    Post subject: Reply with quote

bikerdudematt wrote:
owww and aswell ive got a bit of plumbing pipe on it now about 15cm long just coming straight off the carb and down il see if that makes a difference in power.


Nah, when I said straightpipe I actually meant on the exhaust.

You do really need some kind of filter on the air intake, the K&N one is fine as it's designed to be a performance filter.

Once you have a less restrictive exhaust on it you should be able to burn more fuel at once by upping the mixture, hence more power. Plus it will sound meaner.

As Stinkwheel said though, if you want serious power you need to start looking at cams and the like.
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