Jetting a q-850-AN

[XH29N0G]

I decided to try an annular booster QF Q-850.  It has relatively small venturis 1.39 and a 1 3/4 throttle plate.  I have been using an A/F gauge to bring it into range and have some questions.  

Out of the box, the it had 4.5 pv, 76 primary, 84 secondary, 33 mab, and 73 iab.

I have found that I can get a decent cruise (A/F = 15) with 79 iab.  I have the idle screws out 1 turn and is 9 inches of vacuum at 900 rpm which is about right and a/f of 13.3.  

I also found that I can get a flat curve at A/F 13.4 on full throttle acceleration with mab of 36 and 68/76 (I think I should be a little higher on jets to drop the A/F a few points, but this is pretty close.  The issue that I want to ask about is that the jets are way different than the out of the box jetting.  

I am running it on a ~450 c.i. stroked 383 with performer RPM intake and heads, a 1/2 inch phenolic 4 hole spacer and a .510/.517 cam.  

It runs well, and is more crisp than with the larger venture carb I had on there before.  I have only checked the vacuum briefly on the full throttle runs, but what I saw did not look starved for air (it looked like it was at 1 psi or so).
 

What I have read is the oob should be rich, but close.  I am surprised at how small the jets are that it seems to need.  It was just so rich A/F of 10 or less oob.  My guess is that the annular boosters and small venturi just need less jet to get the gas to the engine, but I would like to hear any information from others.  (I am attaching a 3rd gear pull (starting at about 2200 RPM and going to about 5000-5500 RPM).  I swapped the shooters to 035 and put a brown cam an 50 cc pumpshot in the secondaries to cover the lean spot.

I also recalibrated the A/F gauge to make sure I was not miscalibrated.  

I have not put it on a dyno so I doubt it is optimized.  

What I would like to hear is whether what I have done makes sense, or whether I should do something else, etc....The one thing I have not done is asked quick fuel about it and I assume that should be done.

[68charger440]

I just put a proform 850 dp on my 500" stroker and the Proform oob jetting was 78 and 86.  My a/f is between 9.5 and 10.8 so I am thinking of trying 72 and 80 to get mine to come in line.  I dont know how to calculate how much to jet it down so that is just a guess on my part.  So...  I guess there is a wide range of what what is needed depending on each combo, but you are not alone in having to jet it down quite a bit.

[justcruisin]

I have messed with a few quick fuel carbs (but never an AN) and I have found them all to be rich at idle and part throttle cruise out of the box. Most changes have been with primary mains, IFR's and sizing power valves and pump shot. I have found the installed AB's seem to be good. Your curve seems good but a little too lean for my liking, if you have a good part throttle cruise A/F I would up the secondary main jets a couple of numbers.

[BSB67]

Curious.  Why do you think those are good A/F numbers?

I think the cruise and WOT are too leans as well.

The cruise can be richened up with either the idle circuit, or the main.  Hard to tell the better approach based on you info.

[XH29N0G]

Curious.  Why do you think those are good A/F numbers?

I think the cruise and WOT are too leans as well.

The cruise can be richened up with either the idle circuit, or the main.  Hard to tell the better approach based on you info.

I am open to suggestions. 

My thinking was that cruise was near 14.7 and the car does not buck so it was OK to be at 15.  I agree that the WOT is a little lean.  I was thinking something in the 12.8-13.2 range would be better.  In the end though, my guess is that the best way is to see what works best at the track (which I have not done) or on a dyno (also not done).   

[justcruisin]

What one engine will tolerate another wont, I have tried mine at over 15:1 briefly as an experiment with no "driveability" issues. I prefer to run a cruise of 14-14.5:1, I have no issues with detonation, both audible and from plug inspections. A wide band is pretty good but keep an eye on the plugs, they will tell you what is going on.

[68charger440]

At what point does it become dangerous to the motor even if you can't hear pinging?  15.0 16.0?