I actually have that set, but they are very hard to use and impossible to tell what size they are unless you put a caliper on it. I think you basically have to use a hand drill chug system. A buddies race shot uses a set from Holley/NOS that have a hex bottom end marked for size, but I am having trouble finding them. I borrowed his #67 = .032.

One another note, I found some info on emulsion tubes explaining that the top port affect the low rpm range, the middle affects the middle range, and the bottom affects the high rpms range. Increasing the emulsion tube size leans out the fuel in the corresponding part of the fuel curve. I am not really seeing this as an rpm related issue as much as a throttle position issue but I guess you could make a loose comparison. I guess I will try it and see what happens.

 

FYI, here is the Holley/NOS set.

http://www.holley.com/15992NOS.asp

 

It's rpm related. The more rpm you turn, the more fuel the engine uses(drawing more air in) and the lower the fuel level in the main fuel well. At 2k rpm and WOT in something like a 3 circuit block, the only emulsion port being uses is the top. As rpm increases it draws the fuel level down and uncovers more emulsion. That's what the jet controls, how quickly fuel can fill the main fuel well back up. Proper jet sizing causes the fuel level in the main well to draw down at a controlled rate that works with well size/taper and emulsion to give the proper AFR. Position, size and number of emulsion holes determines how the HSAB affects the fuel ratio curve.

 

So, what if you are just running very light throttle...basically cruising at say 5k rpm? Are you using the top, middle, or lower emulsion port? I would think this is a function of rpm but also throttle position. With a high torque motor in a relatively light car, you do not need much throttle to cruise at high rpm. I would think with the throttle plates barely open, the carb the boosters are not sending much fuel so the lower emulsion ports are not in affect, regardless of the rpm. Am I thinking right?

This is an issue at slight throttle at most any rpm. I notice is a bunch at 3500 rpm because that is where I cruise on the Interstate at 70mph, but it does it really throughout the rpm band when I just have a slight throttle applied.

 

hmm if you have the slight bog at any rpm i wouldn't drill anywhere until this is fixed ..

idle mixture, accellerator pump?

 

That's just it, I cannot get it to lean out without leaning out the entire primary fuel curve.

 

Throttle position will matter as well. Really it's a matter of fuel demand for the engine, but at high rpm with minimal throttle it's using the top circuit, and maybe even the middle circuit at 5-6k. That's something that you'd probably have to test to find out, since it's specific to each engine.

And if your jetting has you correct at WOT but lean at part throttle cruise, then you may want to go UP on the primary jetting to get the cruise correct, and then DOWN on the power valve channel restrictor to get WOT AFR correct again.

That's where I'm probably gonna end up on my QFT....I have to shrink the emulsion a bunch and go to smaller jetting to get WOT AFR close to where it needs to be, but then it gets a really bad lean hesitation/surge at cruise and light throttle accel. So I'll probably have to go up on primary jetting, then down an equivalent amount on the PVCR.

 

Good point. I had not thought of that. My problem is partial throttle is pretty good and WOT is pretty good, but cruise is rich so if I did what you are doing, I worry that my partial throttle (basically running on the primaries) would be too lean. My goal is to get the tip-in or cruise throttle closer to partial throttle on the primaries. If I can get that, I think I can re-jet to get WOT a tad richer and be happy. Right now, If I jet down the primaries, cruise is good but partial throttle is too lean and stumble around pretty bad. I played with the Air Bleeds (both Idle and High speed) and affected things, but could not cure the issue. That is why I am looking at emulsion.

Patrick is pretty atimate about keeping an 8-10 jet spread on the jets, assume to compensate for when the PV kick in on the Primaries. I think I currently have .055 power valve feed ports. Does that sound right?

 

was my thought as well when i read this (worry about part throttle)

for the spread i'd say he wants it to match the PV restriction, so if you want to increase the spread, you'll have to compensate with opening the PVR and vice versa

 

That is correct. On my QFT the jet spread is 6 sizes, again the smaller primary jet compensates for the additional fuel from the PV. If you ran a PV plug then you'd need to have squared jetting. Playing with PVCR sizes and jetting is one way to balance the cruise/WOT AFR's.

The reason Pro Systems and QFT are adamant about maintaining the proper jet spread is so that it works with the PVCR to provide equal fuel delivery at all 4bbls and keeps the AFR balance even across all 8 cylinders. If you go way lean primary and way rich secondary, then at WOT the front cylinders run lean and the back cylinders run rich....an AFR gauge shows a mean so you might get 13:1 on a wideband on one bank, but the front cylinders could be at 14.5 and rear at 11.5.