Fuel Pressure vs A/F Ratio

[65Cobra]

Owning a '99 Busa makes you realize there are a lot of differences compared to other years. I have the original 1999 Service Manual and Supplements for 2000, 2001 and 2002, and the procedure for checking fuel pressure is the same... 43psi with the ignition key ON... not with the bike running... so once I start my bike, vacuum brings the pressure down to 36psi which should be correct.

At one point I set mine to 43psi with the bike running, because I was told to do that more than once... but it didn't go well... the bike ran horrible... so I'm back to what the manual says.

Right now, during normal idle (and 36psi fuel pressure) my A/F is 12.7 which is too rich. In case the fuel pressure gauge that came with the BEGI isn't accurate, I have another one coming.

In the meantime, I know there were some significant changes in the 2003 model but I'm not sure about any in this area since I don't have a 2003 Supplement... hint, hint lease: but if anyone has any info or thoughts about this I'd be interested in hearing them. Thanks

Cobra

 

[OZBooster]

12.7 isn't too bad,
if you have tightened up the plug gap like you should have for the turbo , you will find a better idle at mid 12s than mid 13s,

your already doing it to some degree...fine tune it to what it likes, don't get too hung up over numbers on the pre boost stuff

 

[DCar]

doesnt matter if you have two identical bikes with the same mods and turbo kits. one bike may want more fuel then the other. each bike is like a women. there are no two alike no matter how much they may look it.

 

[65Cobra]

Just my thoughts but... I'm thinking most modified motors tuned on a dyno can easily go there, but didn't think mine would. No internal mods, stock fuel rail and injectors, stock fuel pressure and vacuum at idle, and zeros in that area of the PC3 map. I'd think my AFR at idle would be closer to stock... unfortunately I don't really know what that would be.

There are other reasons I think my bike is richer than it should be at idle, but prefer not going there. So, if the new fuel pressure gauge verifies my fuel pressure setting is correct, not sure what I can do, unless someone has any suggestions.

 

[POWERHOUSE]

Just my thoughts but... I'm thinking most modified motors tuned on a dyno can easily go there, but didn't think mine would. No internal mods, stock fuel rail and injectors, stock fuel pressure and vacuum at idle, and zeros in that area of the PC3 map. I'd think my AFR at idle would be closer to stock... unfortunately I don't really know what that would be.

There are other reasons I think my bike is richer than it should be at idle, but prefer not going there. So, if the new fuel pressure gauge verifies my fuel pressure setting is correct, not sure what I can do, unless someone has any suggestions.

One of the reasons your bike is richer at idle is because it is now breathing through one 2" up pipe, not two big ram air ducts and a large airbox. Different animals! It is very common to have negative numbers in the powercommander in the 0% column, up to about 1500 rpm. They usually end up being between -5 and -8 . . . give it a try.

 

[george b]

when i had my bike dyno'd, my new a/f gauge showed .8 richer than what the tuner's instrument showed. ( tuner shows 13.0 a/f, my gauge would show 12.2 ). pretty shi**y huh? would be real easy to mess things up going by it.

 

[65Cobra]

One of the reasons your bike is richer at idle is because it is now breathing through one 2" up pipe, not two big ram air ducts and a large airbox. Different animals! It is very common to have negative numbers in the powercommander in the 0% column, up to about 1500 rpm. They usually end up being between -5 and -8 . . . give it a try.

Excellent point... didn't think about the air intake Once I finish updating my lines and double check the pressure with another gauge, if I'm still at 12.7, I'll try a few negative numbers in the map... don't worry, I won't overdo it. Thanks for the help.