Evin 25HP 73 are jets carb related or motor related ?

[G DANE]

Friend of mine has above motor. The carb is pretty worn. I have a carb lying from a 35 hp 1979 I parted out. I´ve been told this is a better carb, same bore. The 35HP carb has 49D main jet, the original 1973 carb has 72 main jet. Which jet should we use for the 1973, it has less displacement than the 1979 35 HP ? the 72 or the 49D ? Does anyone know ? Is the jet calculated from the motors displacement or the venturi in carb ?

 

[Dhadley]

Re: Evin 25HP 73 are jets carb related or motor related ?

Each carb is calibrated for the air it flows. Jetting is a small part of the total calibration that allows us to "fine tune" the motor. You may have "tweak" the carb jetting for things like altitude, modified porting / compression or grade of fuel but generally speaking if the carb will bolt on and the linkages line up it will work.<br /><br />Good luck!

 

[G DANE]

Re: Evin 25HP 73 are jets carb related or motor related ?

thanks for your reply, Dhadley.<br /><br />We tried to swap the jets and put the 72 in the 35HP carb, but strange enough it loads up badly, only iddle is fine ?? Will try to swap to the 49D and try. Interesting if it will run better i was told by an ole dealer that the carbs later than 78 should be much better - theese are the types with the little brass tube feeding the iddle and intermediate orifices.

 

[Dhadley]

Re: Evin 25HP 73 are jets carb related or motor related ?

Put the jets in the carb that were in there from the factory. Start from there.<br /><br />Carbs are designed, built and calibrated for the fuel available at that time. So - the later the carb the closer it may be to todays fuel plus advances in engineering / design etc. Todays fuel burns leaner than fuel of yesteryear. Thats why its not unusual to have to rejet some older motors, especially on the idle circuit.<br /><br />Good luck!