I am running a 14" dia, 3" tall K&N with a drop base, IIRC. That gives me about 1" above the choke tower. If I ran an HP with no choke, I could probably get by with a 2" tall cleaner with a drop base. With my current setup, I have about 1/4" between the cleaner lid and the scoop bolts, again IIRC. I may can get a very short phenolic spacer in there, but I will probably need a shorter intake to do much.

 

well since you'd be better off with adjustable air bleeds anyways, i'd say you should grab the HP / Proform main body, a 2" - 2 1/2" filter, and a 1/2" - 1" spacer.

 

That's good. The load eases up and the car should lean out when the cars mph catches up to the engine rpm.

If you can't get a spacer, they make thick gaskets for that same thing. Not quite as good, but better than nothing.

The proform main bodies work. They just need too much work. The holes in the main body are usually off and need to be fixed to get the main body and throttle shaft to line up. We just took a HP main off because we wanted the air bleeds to adjust the fuel curve with boost. But the engine was so small and boost was only 6 psi, it didn't have any signal. Ended up putting on the 650 main body with straight legs back on after drilling and tapping them. But this app is plenty big for it.

 

Dustin, tell me more of this thick phenolic carb gasket you speak of (I have a 4150 square bore). I know it may not be ask good as a spacer, but since this is what I have for right now...

 

On a two circuit carb like the 4150 with no air bleeds, how do you adjust the mixture under very very light cruise? Does the idle mixture screw affect the transfer slot at all? I don't think the main circuit jet affects the transfer slot at all, does it? Theoretically, should the idle AFR and transfer slot AFR (for lack of another description) be the same?

In a two circuit carb with air bleeds, what air bleeds affect what circuit?

Sorry for the slow learning curve.

 

All holleys have air bleeds, just not all are adjustable. Your carb has them, but they are just very tiny press in style.
If you are rich at cruise and good at idle you can drill out the low speed air bleeds. there are 8 in total, 4 for the high side and 4 for the low side. Low is when the air flow it low, like light cruising. The high sides controls the higher velocity. They all control the curve of the flow of gas, and emulsion.
Pic of what your should look like.

http://www.mustangandfords.com/techa.../photo_25.html

I'll go home today, and find you a book I bought when I first got into it. It'll give you a good idea of how a carb works. You have a decent idea now, but still flying a little blind. The book will help put it all together. I certainly no expert, but I know enough to get myself into trouble. Then you will really get a kick out of the forums when people give out tech advice on carbs.

The idle mixtures screws let more fuel pass at the same vac level. As the velocity speeds up, more is pulled out. If it isn't enough, that's when bleeds and IFR comes into the picture.

 

Sorry it took so long. I did ya pretty good though.
http://www.amazon.com/Holley-Carbure.../dp/1884089283
Breaks it down "Barney style"

 

Excellent. Thank you.

I did a jet and power valve switchover Sunday, but it has been drizzling every since, which would give me poor AFR readings anyway. I hope to get her out on Friday for a 100 mile drive. I had 69 jets in the primary and 67 jets in the secondary. I changed them out for 66 jets in the primary and 68 jets in the secondary. I also took out the 2.5pv and put in a 7.5pv. When I fired her back up to check for leaks and set the idle, my vacuum was down and AFR was up at idle. I reset the idle for around 13.5 @ 850. The throttle response was good off idle, which is one of my preliminary tests. Sustained open throttle at 3500 yielded a mid 13.5 or so AFR. I will report again on Friday after a drive.

I am looking into a K&N stub stack to see if it has any affect on air flow, AFR, and AFR/vacuum stability.

 

You gotta keep that carb fueling square. Depending on the PVCR's (little tiny holes behind the PV), your PV is good for 6-10 jets. So right now your jetting is really more like 76 front- 68 rear. What you do to the front, you do to the rear.Just food for thought.

 

Ok, here is my carb tuning blog for the day. It was cooler this morning 45* with 40% humidity. The car is definitely more lean. Idling and very very light cruise is set about right (13-13.5). At cruise running on the primaries only, I am running 15.5-16 AFR and the car is lean stumbling. Under full throttle, it is a little more lean than before (12.5-13), so I think the primary and secondary combo is about right, but the primaries are now too lean.

From what I have read, one jet size should not make that much difference in the AFR, but on the primary side, one jet is equal to about 1:1AFR difference on my motor. I went from 69 to 66 on the front and it changed the cruise AFR about 3:1 AFR 12ish to 15ish. At least the motor is cleaning itself out some at those levels.

I never saw the power valve affect the AFR during cruise this morning. I pulled the vacuum gauge out, so I am not sure what the cruise vacuum was it obviously was not getting low enough for the PV to help out. From what I have read, the double pumper 750s have pretty small PVCRs compared to out carbs because they are not intended for street cars. Maybe that explains the lack of difference from the PV, but I think it was just not opening. At any rate, I did not see anywhere close to 6-10 jet size difference in the AFR at any time. The engine really never loads up, so I never see a drop in vacuum unless I hit the throttle...PV may not help me much.

I will see what the car does this afternoon when it is warmer (70s). If the AFR is still in the 15s, I will jet up one size on the primary and see where I am tomorrow. What I have learned this motor hates AFR in the 15s (stumbles around like a drunk guy). It also cannot handle AFRs in the 10s (belly is too full and tries to go to sleep). Maybe my AFR meter is a little out of calibration, but I am scared to recalibrate until I get this all lined out. It is all relative anyways at the point.

I know as a rule of thumb, the front primaries should be leaner jetted than the secondaries. If I installed a 6 jet difference, it would be way lean under cruise and way rich under WOT. Think this motor is going to want to be more square given that lack of affect the PV has.