Fuel regulator question

wdonovan
Registered User
Joined: 20 Sep 2016, 15:01

27 Mar 2017, 19:11 #1

For you bike engined guys... When my car's previous owner had it converted to Hayabusa 1300, he installed a big Bosch pump and I believe a Holley fuel regulator. It is a bypass regulator like I have used on car engines in the past. It bleed of to a return line into the fuel cell. The regulator has a vaccuum port which is not connected to anything. Normally it gets connected to the intake manifold so at idle it pulls the pressure down to not have to shorten the injector pulse width beneath its capability. The car seems to idle fine with this port not connected but when I saw it, it seemed to me like a serious safety issue. It points roughly toward the headers. In the unlikely (but still possible) event of a ruptured diaphragm, this thing would try to empty the fuel cell onto hot headers. I either want to run a line into the manifold or put in place a puke tube to the rear of the car.

My questions are: 1) Is this vacuum signal needed or even used on a bike engine? What do you guys have regarding this arrangement?
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George Dean
Registered User
Joined: 01 Oct 2002, 09:45

27 Mar 2017, 23:08 #2

    The port on the side of your regulator should not be connected to anything.  It is there to increase the fuel pressure when the engine is under boost only,   You are correct if the diaphragm gives up fuel will come out,  I keep a spare in the shop now so my dyno is not down while waiting for a new one,
    George
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wdonovan
Registered User
Joined: 20 Sep 2016, 15:01

28 Mar 2017, 20:12 #3

Thanks much George. I thought it had use in an N/A motor as well. I remember from old hotrodding days, when you put big injectors in, you could not get the pulse width low enough at idle so they pulled down the fuel pressure some with vaccuum. I will install a puke tube this weekend that extends to the very back of the chassis. Glad I saw this.
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David Ferguson
Registered User
Joined: 20 Mar 2000, 16:17

30 Mar 2017, 16:04 #4

Engines can be mapped with our without it connected.    Since George uses mostly factory ECUs, they are tuned with it disconnected.  
I prefer to always reference the fuel pressure to the manifold pressure so the fuel pressure across the injector is close to constant, making it easy to do mathematical fueling corrections.
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wdonovan
Registered User
Joined: 20 Sep 2016, 15:01

01 Apr 2017, 13:20 #5

Now Im really confused. I know I should use the setup that the ecu is mapped for. This car has a stock ecu so I should mimic the stock regulator arrangement. But when I googled photos of a busa regulator, I get pic of a pump/reg piggyback thing that clearly shows a nipple on the spring side of the reg. Factory shop manual dies not clear this up.
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