NX250 jetting and coolant temperature

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scrambler
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NX250 jetting and coolant temperature

Beitrag von scrambler » Mo Feb 23, 2015 8:42 am

The carbs of all NX250 versions (even the 29 HP AX-1) are identical, except for the jets. The 1988 (249cc) version got 138/38 main/slow jets (12,5KW: 145/38), the 1989-1990 142/38. The 239cc from 1991 onward 140/35 (12,5KW 145/35).
The cooling system of the Nixe is well dimensioned and very dependable, overheating and other problems are rare. With my 249cc version and the stock 142 mainjet I have never seen the temperature warning light in 15 years (ok once, when I was curious whether it works at all and tested it by heating the thermo unit with a blowtorch) and the fan is running very rarely (only when going at very low speed for some time).
So usually a cooling temperature gauge is just a gadget, if everything is stock. But if the airbox or muffler is modified the jetting might need to be adjusted. In this case one can utilize that the coolant temperature is sensitive to the main jet. I tried a 138 main jet once and the coolant got really too hot at full speed. After switching back to a 142 main jet I got 10-15 degree less. I measured it with a trailtech Vapor (it shows the max temp and max speed during that trip).

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Or you could get yourself a thermo radiator cap http://www.ebay.de/itm/D1-SPEC-RACING-R ... 2ed982a213. Radiator caps of car and motorcycle are pretty much standardized - as far as I know there are only two types, „big“ and „small“ head – and the NX radiator needs a big head cap. The only other difference is the max pressure before the internal valve of the cap will open – it’s written on the cap: 0.9, 1.1, 1.3 or 1.8 kg/cm2 - the NX cap is labeled 1.1

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