speedingmotor...
Two Stroke Sniffer
Joined: 24 Jun 2014
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 Posted: 15:51 - 24 Jun 2014  Post subject: cg125 k1 1979 - aircone/carb questions |
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hello
first post here, but definitely have been trolling here a while since i got my bike ( a year ago)
a month or two ago i took off the airbox and put on a cone air filter, rejetted the main jet from 100 to 110 and dropped the needle a notch to get more fuel. i wasnt able to change the pilot jet because the piece i ordered wasnt the right type of jet, but i will change it soon.
a few weeks ago, on a hot day, and a long trip the bike overheated, which i assume was partly due to carb adjustments, partly due to weather and partly due to how i was riding (pretty high revs)
i would like to take long trips on the bike, but now am a bit hesitant.
so my question: in general what other adjustments should i make to the carb (should i go up another main jet to 120? should i not have dropped the needle? etc) and what precautions should i take to keep the bike from overheating...
i changed the plug and will ride a bit, check the color and see about rich/lean
thanks
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P.
Red Rocket
Joined: 14 Feb 2008
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speedingmotor...
Two Stroke Sniffer
Joined: 24 Jun 2014
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| Posted: 16:55 - 24 Jun 2014 Post subject: |
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hey paddy
thanks for your response
there is really no gain in acceleration or power with more air and fuel? is the motor too small?
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Teflon-Mike
tl;dr
Joined: 01 Jun 2010
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Posted: 18:59 - 24 Jun 2014  Post subject: |
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| speedingmotorcycle wrote: | there is really no gain in acceleration or power with more air and fuel? is the motor too small? |
Power = Cylinder Displacement x Cyclinder Pressure x Engine Revs.
All the carburettor does is mix fuel and air in the right ratio to make it go bang. There is NO 'magic' carb or carb set-up that can find you a huge power gain; its just NOT in what the carb does to do it.
What limits power is how much 'charge' you can get into the engine; carb will be able to flow far more charge than the engine can so its not the weak link; The PD26 carb used on the CG which makes about 10bhp is used on bikes making over 20, so there is no 'restriction' in it.
What limits the power a CG125 might make is that it is a little engine, with little valves, so it can only suck 125cc of charge per cyclye at best, and the valves aren't very big, so you wont even get that; then those little valves aren't opened very far or for very long, due to the cam-profile; so even less charge might be sucked into the motor.
CG has a simple 'shared cam-lobe' push-rod engine; the push-rods lmake the valve train heavy, which limits the amount of acceleration they can put on the valves, as well as the engine revs the engine can turn; the shared cam-lobe then also compromises the valve timing, which has to be a compromise between the duration best for the inlet and the duration best for the exhaust, as the single lobe opens both valves.
Even if you got seriouse with a CG engine, trying to tune one, these compromises would limit how 'wild' you could go with cam timing to be able to find more power; and with such small valves and such heavy valve train, would ultimately be rather pointless.
Its the Irishman asked for directions joke; "Now den, I wudden be wantin to start from here, now!"
Because the CG push-rod engine was actually DESIGNED as a low cost, low maintenence, low power engine; when engines with far more performance potential were comonly available, with duel-lube over-head cams that had the scope for much more optimal valve timing, on each valve, lower valve train weight, so they could more easily and safely rev to find power, and often had bigger, valves.
You would get more power from simply swapping the engine to an XL125 engine, far more easily and far more cheaply, than almost anything you could do to a push-rod CG engine.
So, yeah, as Paddy says, stick it back to stock.
Its not that the engine's too little; its just NOT designed to have more power than it does, and has no scope to make more than it does; and if you want more than it delivers, easier to get a bike that HAS more power as stock than bug about with what you got.
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My Webby'Tef's-tQ, loads of stuff about my bikes, my Land-Rovers, and the stuff I do with them!
Current Bikes:'Honda VF1000F' ;'CB750F2N' ;'CB125TD ( 6 3 of em!)'; 'Montesa Cota 248'. Learner FAQ's:= 'U want to Ride a Motorbike! Where Do U start?' |
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