im trying to tune my demon 650 d.p. and i was told that if i tap my secondary pump arm that the motor should pick up and if it doesnt, it is too rich and i should drop the jet size. i never heard of this before and was wondering if it was true.

 

Lunch meat.

It will pick up if it is lean and you tap the pump arm. If it's rich or just right, it will drop off.

However, when you're sitting in the driveway performing this little "test", the carb is operating off of the idle circuits. The jets operate in the main and secondary circuits, when the throttle is open enough to draw fuel through those paths.

Chalk this one up to McDonalds parking lot monkey spank (trademark pending).

 

i forgot to mention he said to do this with the throttle cracked

 

It's a silly way to attempt to tune a carb.

With the throttle cracked enough to get past the idle circuit, the engine would be reving pretty high. It still wouldn't give you meaningful information. If it is just right, extra fuel should slow the RPMs down. The only way it would raise RPMs is if you are lean, and grossly lean.

 

thanks, where would a good starting point be? the jets are 70/78 right now out of the box and the timing is locked at 36*

 

You can either get an air/fuel mixture meter, dyno tune, make runs at the track comparing MPH with different jets, or read the plugs.