Blow-through Carb vs. Regulator issues..

[Y-TRY]

I Ninja'd another thread with this issue but decided to move it here for some help.....

....CarbShop Blow-Through carb
Aeromotive boost-referenced fuel pressure regulator....

I'm having a problem with my regulator adding pressure when there is no boost. Under normal loads the pressure will increase along with rpm and start to really flood the engine by about 10psi. It does not appear to be an issue with the gauge.

The problem stops if I disconnect the boost reference line. If I bypass the boost reference the system works fine, I just can't go into boost in this situation for fear of starving and leaning out. The regulator is there to offset the pressure in the bowls when boost is present.

It's like the regulator is sensing boost and adding pressure according to plan. However, there is no boost. It happens during normal driving (not WOT) So, instead of compensating, it's flooding the engine. With no boost-pressure in the bowls it's simply flooding them over and pouring raw fuel out the vents. The regulator is sensing that there is 3psi in the hat, for whatever reason, and forcing 10psi into the bowls (7psi base setting)

The main indicator for this is the fact that there is no problem with the boost reference disconnected. Pressure stays rock-steady. Fuel pump speed and voltage is steady also. This also eliminates the return line as being a restriction.

One possible issue: The boost reference line is connected at a "T" off the hat. The other side of the "T" goes to a line connected to the baseplate, per CarbShop. Because they are tee'd, it is possible that the signals to the regulator are being affected by pressure to/from this line. But that is my current diagnosis.

Can you guys help? What should I do?

[camcojb]

Get rid of the tee. The regulator needs a single line from the hat to the regulator, not anywhere else. The fuel pressure needs to react to the hat pressure which covers the bowls, nothing else.

Are you running a bypass valve?

Jody

[Y-TRY]

Thanks, Jody. I have emails in to Aeromotive and CarbShop, also. Mainly, I want to know if the line from the baseplate is necessary at all. I know CutlassKid is running his without this provision hooked up with no problem. I think I remember it being a way to pressurize the throttle shafts under boost to keep them from leaking (?). But it just seems like it's sending the same signals from the manifold to the boost reference line. If this theory is correct, then the regulator is more-or-less referenced to the manifold right now instead of the hat, ya follow?

I'll be back home, where the car is, over the holiday and play with it some. I'll also bring it back up here where I'm working so I can mess with it more than a couple hours a month.

As for bypass- I think you are speaking of boost bypass? I'm running a blow-off valve, but not bypass (I think you are referring to the centrifugal supercharger style bypass valve, right?). If so, no. Just the BOV.

The boost gauge, turbos, wastegates, BOV and BTM are all running from actual manifold pressure while the regulator and said baseplate line are sourced from the hat pressure. As a matter of fact, I originally had the regulator referenced to the manifold and it was doing the EXACT same thing. A call to Aeromotive corrected that, but the problem persists. I think we're on to something. Dang, if the car weren't 200 miles away right now.....

[camcojb]

I was thinking centrifugal for some reason. Another question; is this a bypass-style regulator or is it dead-headed?

Jody

[Y-TRY]

I was thinking centrifugal for some reason. Another question; is this a bypass-style regulator or is it dead-headed?

Jody

It's a bypass. It's located in the return line (after the carb, back of the "log", not between the bowls).

[Y-TRY]

Okay, word back from Bob Vbranic is that the line from the baseplate uses pressure from the hat to seal the throttle shafts, but it is NOT open to the manifold and NOT a vacuum source. FYI.

[Y-TRY]

Minor update: Long-story-short, I'm an idiot. There ya go.

I originally had my regulator referenced to the manifold pressure. It was really flooding the engine over. So, to try and stifle it some, I lowered the float levels.

I corrected the regulator reference to the hat, but never reset the float levels. So the regulator was finally working properly, and what was showing up as flooding before was now actually leaning out. The symptoms felt the same, so I assumed it was the same problem.

The tech at Aeromotive asked me one simple thing: "How do you know it's flooding and not leaning out?" That set me back for a second and I was like, "gee you're right".

So I adjusted the floats back up the the appropriate level and the stuttering is fixed.

On another note, just out of curiosity, I performed the following test: I took a spare boost gauge and hooked it to the hat. Then I routed the line up the cowl and taped the gauge to the windshield (redneck HUD). I can now tell you with quite certainty that there is quite a pressure difference above and below the throttle blades. At moderate load, 2000rpm I showed nearly 20hg vac. in the manifold, while the hat was actually seeing about 2psi boost. This correlated perfectly with the increasing fuel pressure.

Even at idle, I see about 17hg vac. as the hat is definately pressurized. As a matter of fact, the pressure would blow fuel out of the sight plugs when trying to adjust the level with the hat on. This gives it the false impression that the bowls were too high.

Anyway, all of this is just FYI. Hopefully this info will help someone else along the learning curve.