The pumper carb works really well in my opinion as it allows you to set up as an optimal slightly lean but squirts a little bit of fuel when the throttle is twisted in anger for good pick-up. I have just read a write up of the new XR125 and stone me (Jehovah! - Life of Brian!) the engine looked like an electric start CG engine!! My brother fitted a CG engine into an XL and the CG engine was really good off road and also seemed to respond quite well to the small diameter XL125 exhaust pipe with only a 22ish mm I/D. I think the XL/CB's lack of squish has a lot to do with this as it appears to be designed as neither a 125 or 200, the 200 or 185 has an offset squish (opposite the spark plug) but the squish is flat.Ĭylinder head work boosts performance all-round! My friend old modified CG used to go up an hill in 5th gear but the clutch had problems coping with the extra power and slipped a lot!Ī WORD OF WARNING CG125 valves being very small tend to get very hot under hard use, the valve seats also pit easily because of this not allowing the valve to seal well which means that the valves get hotter due to blow-by and not so good heat dissapation hence many CGs drop their exhaust valves so stainless exhaust valves are highly recommended! On the cylinder head I am working on that is why I have opened up the exhaust port a lot to help the gasses expand quicker thereby holding less heat. The CG125 engine is as good as in a lot of ways to an XL/CB engine, giving far more torque and fuel economy but only lacking in top-end. The CG125 head has a nice squish area compared to the XL/CB125, this is due to the CG having a very small exhaust valve ( not good!) which means that both the valves are moved closer to the centre of the cylinder head.
I've modified the valves slightly as on the back of the valve close to where it contacts with the valve seat there is a ridge which I ground smooth and also where the valve stem meets the head there is a pronounced step which I smoothed off. I've also raised the top of the port slightly around where the valve guide enters. I've opened up where the exhaust port exits as it goes from a small and quite choked up port into quite large exhaust.
I've also ground the end of the valve guide smooth, re-angled the inlet port by raising the roof and the floor (with epoxy) a little to give it a larger radius where it curves down into the engine.
Basically the valve seats/throats are mismatched where they meet the ports. I will try and post some pics when I borrow a camera from work.ĬG heads tend to respond massively from porting work. I am soon to be finishing a porting job on a CG125 head.
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