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 Post subject: To much fuel pressure
 Post Posted: Sun Jan 20, 2013 1:52 pm 
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I recently put a belt driven pump on my car and the pulleys I had, it was turning the pump too fast. To the point that I could totally back out the screw on the regulator and still have over 8 psi at wot. So this cause some issues with unstable fuel pressure and such.

So I installed a new pulley in there and now the regulator will control the fuel pressure at WOT. I got it back down to around 6 psi. I haven't run the car will the new pulley yet. What effects to the AFRs, will the excessive fuel pressure have? Could it cause a leaning of the fuel pressure because its aireating the fuel? How much have people seen it change? In the good air, car seems to be running a bit off and o2 shows it a tad lean(13.2-13.4). I jetted it up but didn't get a chance to run it. But now i got the fuel pressure under control.

Thanks all!

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 Post Posted: Fri Jan 25, 2013 5:52 pm 
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So am I just asking a bad question or does nobody have any experiances with fuel pressures effect of fuel mixture?

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 Post Posted: Fri Jan 25, 2013 8:16 pm 
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I thought I had posted something on this?? Obviously not.

Fuel pressure will have an effect on float level if it's set at one pressure (low) and then run at a higher PSIG down track. Higher pressure will make the float level higher which "should" make it richer also, or, if the pressure is high enough it could blow the needles off the seats too and that would make the fuel level REALLY high.

It's been stated here many times that fuel pressure needs to be set at what it will be down track and this is especially true with a belt drive as it's pressure varies with engine RPM. If you got 8 something down track, then that is what the floats need to be set with. If it's 6, then same thing applies.

You stated it showed lean AFRs?? If there was a miss down track from too much fuel, ie, flooding, won't that show up as lean also? After all, an O2 sensor measures oxygen not fuel. :-k


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 Post Posted: Fri Jan 25, 2013 9:04 pm 
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It shows a couple tenths lean compared to its best pass ever. However the other thing is I am running vp113 which is an oxygenated fuel vs 110 no oxygenated. So I am still playing with it to see what the engine wants.

As far as the missing, I don't feel anything, it feels like it pulls strong. Also egts show higher than they were before too. I plan on putting a fresh set of plugs in next outing so I can get some plug readins.

Last time I increased the jet size, it picked up.

I haven't messed with jetting too much because I have been struggling trying to get a handle on this mechanical pump after trying many things, I finally decreased the pulley ratio and it seems to be under control now. Before hitting the converter, I would see 8-9 psi with the regulator adjuster backed all the way out. Now I am showing 6.5 with the regulator allowing me to adjust the pressure. So I am hoping my fuel pressure will be consistent now.

Just trying to get some perspective on this as to why it is showing lean.

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 Post Posted: Fri Jan 25, 2013 9:32 pm 
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I'm sure you already know this, but oxygenated fuel requires more of it so you're probably going to have to go up 2 or 3 numbers on the jets to get best MPH.

Scott Smith runs Q16 I believe. Maybe if he reads this he can give you some info on how much more jet you will need.

On another note, belt drives with a bypass regulator is something I've never fooled with. My belt drive pump with a built in bypass is just as happy with gas as it is with methanol. I don't run but 6.5psig or so down track with either since I use PCI fuel bowls on my methanol carburetors. That thing idles @ around 2.5psig, the bypass is set to 10psig and the regulators I run are set at 6.5psig.


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 Post Posted: Sat Jan 26, 2013 1:01 pm 
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I jetted up 3 sizes right when I switched to the 113 and gone up 2 more since then. I just think this pulley ratio was causing me some grief. I will be running it next weekend, hopefully I will be able to do some tuning now that I think I got my fuel pressure under control.

I have a built in regulator in my pump, but I use the bypass. Since my fuel tank is in the rear, my theory is its better to keep the fuel moving.

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 Post Posted: Sat Jan 26, 2013 6:13 pm 
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The BLP belt drive I use has a 2 to 1 ratio on the drive, ie, 8k RPM at the crank and the pump is turning 4k RPM, etc.

I've had that thing forever (since 1998 if I remember correctly) and it just keeps on working and working and working!!! Damn shame I can't buy tires that will last that long, hey!! ;-) Before that I went through 3 Aero electric pumps in 13 months and the last one was after the 1 year warranty ran out. $300 worth of junk in the round file. ](*,)


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 Post Posted: Sat Jan 26, 2013 6:47 pm 
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I have a 2-1 ratio now, before I had a 1.75-1 ratio. So I knocked off 500 rpms at peak rpm.

I have an apd pump, best I can tell, they use the same gear sets as blp, just a different housing. Really not much to wear out as long at you don't run it dry.

So how do you set your float levels with that pump?

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 Post Posted: Sat Jan 26, 2013 7:03 pm 
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Run the pump with a 3/8 electric drill. Close the chuck then use the outside of that to drive the pump. And you don't even have to start the engine. If I need to lower the level I just loosen a lower bowl screw and drain it down a bit.

Of course, once I establish where they need to be, then what I do is use a drill shank of the appropriate size to gauge the float them then check them after they're installed.


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 Post Posted: Sat Jan 26, 2013 10:00 pm 
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On a 1050 with no skirts I used a .128 jet on last years Carb Shootout Dominator. This year the change to a smaller cam still netted within 6 HP of last year, the new QFX body 1050 ended up at .116 and may have made more if I had been able to pull more fuel out. Both on VP 113, so the jetting is really dependent on the engine combination and maybe a little different due to the difference in the old style Holley and the QFX body.


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