How to tell if the second barrel in the carburetor is opening

[justaguywitha720]

I was driving and I feel like I can get more power out of my 720. One of my friends said that my second barrel in the carb might not be opening. How can I tell if it opens

[datzenmike]

It's hard to simulate a load when sitting still and just revving it. By the time there is a chance that the secondary is or will open the engine is revved out of sight.

 

 

See the cone shape with the round cover on top and the rod sticking out of the bottom? That's the vacuum diaphragm and it pulls upward opening the secondary with a vacuum signal from the primary and secondary side but only under heave throttle and when revved up and needed. If you watch it and repeatedly blip the throttle revving the engine higher and higher then floor it you might see it move.

 

I would just make sure it free to open. Engine off, hold the throttle at least 60% open to release the interlock on the secondary. Push upwards on the rod and it should move. It's very stiff. If you can't get it to move perhaps the throttle plate is jammed. Use a searchlight and look down the secondary for an obstruction.

[Stinky]

Easy, when the 2bbl kicks in, you will get get a pronounced push, back in to the seat.  And, your tires will chirp.

 

Seriously now, you will get about 75% of your power from just the 1st bbl.  Get it up to at least 3,000 rpm, put your foot on the accelerator, up to the point where you feel the peddle get stiffer.   You can feel for it w/o the motor running.  That is the point where you are starting to push on the secondary's spring.  Then floor it, does it run a lot stronger?  Or is it just a little stronger.  I will run a little stronger on 1 bbl and a lot stronger if the secondary kicks in.

 

It will have to be rapped up, rpm wise, for you to tell.