XJ600 Seca II Fuel Pumpery

There has been a lot of talk about the Seca II's fuel pump lately and whether to know how effectively it is functioning. So I got to thinking -- is it really necessary? Since the carbs are turned up into the tank, I suppose it's needed to get the gas uphill. Okay...

It has a secondary vacuum line (vacuum line from petcoque to #1 intake being primary) hooked to the #2 intake for more pumping power. It's not electrical or anything, just added gas suckatory. However, is the vacuum from the petcoque line not strong enough to get the gas uphill to the carbs? What if I ripped out the fuel pump and put a fuel line from the petcock into the carb, and all the vacuum was coming from the petcoque...would the gas make it up the 7-inch climb?

Every time I look at the fuel pump, I ponder it's existence. You can almost disregard the picture, it's just what I skribbld down when I started thinking about this earlier today (while I was supposed to be working).

 

Aren't the Divi's carbs downdrafts? The layout looks very similar to my FZ750's, which is similar on the FZ(R)400/600/750/1000 of the era... I can't imagine Yamaha putting more engineering into the fueling system for the Divi.
The vacuum SHOULD only be used to open the petcock, not to 'pull' any extra. It shouldn't be a high-pressure pump, as it's the floats controlling the amount of fuel into the bowls, not the pump. Pump should increase with revs.
This is based off my knowledge of the FZ's however. My XJ600 is from '85. ^^

 

Yeah, I was going to say you missed the whole point of the "vacuum operated" part.

Sorry to say, the vacuum is nothing more than a "signal" to turn the fuel flow on/off. No "suckatory activity" being engaged in.

Rethink. Yes, you need the pump. Do you really think Yamaha would go to all the time, trouble and expense to engineer it into the system if it were completely unnecessary?

 

Yea that makes sense, thanks for the clarification. I guess I just needed to learn a little more about the system!

 

Hey, Andrew - I like your "French" pronunciation of the name for the fuel tap. An excellent way to get around that silly censorship!

 

Heh... didn't notice that! lol

 

Haha thanks, I've got a bad habit of spelling spelling things that way and I have no idea where it came from.

 

"Suckatory activity"........someone buy that man a cigar!