Fuel Pressure


My understanding is the fuel pressure at idle should be 43 psi, but is that with or without the vacuum line connected to the regulator? If I adjust the fuel pressure to 42-43 psi without the vacuum line connected (and plugged), once I attach the vacuum line it drops to about 37-38 psi. Not sure which is correct. Thanks.


there should be a check valve inline so that the fmu doesnt see vac but does see boost

on a standard regulator it is different you let a standard 1:1 see vac


Okay, I have to admit I was trying to keep this easy, but you just had to go there didn't you Pinky. :laugh:

I have a BEGI 30 Series regulator (2035) which has an additional bottom chamber that is a 1:1 regulator. This model incorporates both a R/R regulator and a 1:1 regulator into a single unit. As a result, the hose from the throttle body goes to a Tee fitting, with one line going to the R/R chamber like all their models, and the other line going to the 1:1 chamber.

I know you and I discussed the check valve before but apparently installing the check valve inline before the R/R regulator is for users who what to use the BEGI 20 Series regulators (i.e. 2025) without a 1:1 regulator, and it does work so your advice is solid. But if someone adds a 1:1 regulator, or like my case, uses a BEGI 30 Series regulator, then the check valve has to be moved from it's inline location back to the R/R Needle Valve outlet or it defeates the purpose of having a 1:1 regulator.

When I purchased the 2035, I thought a 1:1 regulator was always required, but obviously that's not the case. At first I was slightly disappointed, but I've read where using a 1:1 regulator with the BEGI is supposed to steady the base fuel pressure and create a more accurate fuel curve during the transition from vacuum to boost. So, with that in mind, I feel better, but I also have to leave the check valve at the Needle Valve outlet.

After I posted this topic my brain's time delay finally kicked in and told me to check the Service Manual, duh... which I did and it says "the fuel pressure regulator... keeps the fuel pressure applied to the injector at... 43 psi higher than that in the throttle body at all times" Also in the part that explains how to check the pressure at the regulator says nothing about disconnecting the vacuum hose but still says it should be 43 psi.

So I guess I answered my own question and have to make an adjustment so it's 43 psi with vauum. But if you, or anyone else for that matter, have any other comments or opinions, please let me know because I'd be interested in hearing them. Thanks.


Interesting question because the 99-00 was vac referenced but the 01 + was intank and not referenced, so if your bike is 01+ you may still be better running a check valve or spend more time on the dyno doing part throttle stuff ????


I didn't realize there was a difference OZ so that's a good point. I do have a 99 with an external fuel pump and regulator that's vacuum referenced. I puchased the manual back then so it only addresses that year model and I've only recently been finding out about the differences with the 2001 and newer models. I'll readjust the fuel pressure tonight for 43psi with vacuum, then move on from there. Actually this is good because the new logs I make afterwards might come out a little better. Having this forum is a blessing. Thanks to you and Pinky, and everyone else, I'm feeling better about things as I go on. :cheerleader: Okay, maybe not that happy.
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