urban_cowboy

Yeh...given that it did react how you would think it would, I am going to increase the top port size and decrease the bottom port sizes in a attempt to meet closer in the middle AFR wise. I may blank off the bottom two ports to see what it does next...It is definitely leaner with more throttle open. I know people say that emulsion ports are dependent on rpm and thus air flow velocity, but it seems like on my engine is it more a matter of throttle position...

Thanks for listening and for all the help. I feel like when I am done, I will be able to tune ProStock cars .

67mustang302

Throttle position will matter as well. Really the emulsion level is a matter of engine fuel demand, which is based on rpm vs load.

valley firearms

Good news for me. I finally got rid of my lean spot at cruise. I increased my primary jet to 84 and she was way too rich. This told me I was heading in the right direction. I dropped it down to 79 and dropped the IAB to .079 as well. Now she cruises at 13.5-14. All other circuits are good as well. I got to changing things so much I was chasing my tail. Patrick made the primary jet number and the IAB number the same when he built the carb. I knew I needed to be a little richer so I matched them up as well with the 79 jet and the .079 IAB and it's just right.

urban_cowboy

We have been suffering from Tropical Storms this week, so I have not gotten the pony out of the garage in a while. On my last trip, I changed the top emulsion port to a .035 and left the others .028, .028. blank, and .030. I saw a little increase in the cruise AFR up to 13.0-13.3 but I saw a tremendous change in fuel economy. I am not sure whey I did not see any more of a change in the AFR but my ecomomy went from 11mpg originally to 13.5 with the current setup...wow. I am afraid to go much bigger, but I may try a .038 to see what it does. I did one or two WOT pulls and saw the AFR stay in the mid 12. It moves around a bunch, but not terrible. I still see a leaning out when I accelerate just with the primaries. If I give it enough throttle to get into the PVCRs, it drops back down into the 13s, but it raises up to 15 if not. I am thinking I may try smaller emulsion ports in the second and third port down to see what happens.

All in all it seams to be getting better. I was surprised I needed to make as many changes to the emulsion package on this Pro Systems carb as I have. I attribute that to it being a 950 with a light trigger on the boosters, so if flows fuel easily and quickly. A friend told me that tuning the emulsion ports ports is a good way to ruin a good carb. That continues to bother me, but I am only really messing with the primary side...the secondary side when I get into them, seem to behave correctly.

urban_cowboy

The fuel economy thing was a fluke. I drove the car last weekend and was back to 10mpg, but I did discover my issue with cruise AFR. Through a strange series of events, I ran tested the affects of various sizes of ports on the top emulsion and IFR. Here is what I found. During cruise, both my main circuit and transfer slot circuits were flowing fuel. As I open the throttle blades some more the transfer slot would cut out and I would start running basically only on the primary booster circuit. So, I was getting a good 13.5:1 AFR on the transfer, it would go rich during cruise at 13:1, then go more lean as I opened the throttle more and started running just on the primary (vacuum is too high for PV to kick in during these tests). I ran the IFR up to a .038 from a .036 and cruise went way rich...if I dropped the main jet...the cruise AFR would come down...bingo. So I really could not increase the top emulsion enough to affect the primary booster circuit enough to help the cruise AFR. It would help a little but not enough and the rest of the fuel curve on the primaries was too lean. I then lowered the IFR down to a .034 and kept the main jet up a notch from where it was 72 to a 73 and the car ran so much better. I dropped the top emulsion port down to a .031 and the third port down to .025. Stock on that billet block was a .028 on the top three ports but cruise is still too rich for that and main primary leans out too much. Now cruise is mid 13s with the AFR during the primary circuit going from mid 13s to 15, which it still leans out but not terribly. The only hiccup is the transfer slot circuit is now kinda lean. You do not notice it until you put around town in traffic. Always a compromise right? I will swap a stumble in traffic for more efficient and more power going down the highway. That is really how I discovered this. I was trying to richen up the transfer slot circuit and found that it was staying engaged during at cruise which was causing my problems. Basically if the transfer slot AFR is good and the primary circuit AFR is good, then during cruise when they are both on, the AFR is down in the 12s.

kalli

sounds you are having a lot of fun with this now. I am happy with the ever so slightest hesitation off idle. I will try with a tiny bit more idle mixture (going rich). If that doiesn't cure it I'll go back to where I am now. I'm happy with it at any other situation.
what mpgs would you get if you are easy on the thottle (if that ever happens). 10mpg is quite heavy

urban_cowboy

The latest thing I have done is swap out the 1 3/4" throttle blades with holes in them for ones that are solid (holes in the blades are sometime drilled when too much transfer slot is exposed during idle...my ProSystems carb came with these but I have never needed it before). This has allowed me to open the throttles up a little more at idle but still have my idle screws respond (now out 7/8 of a turn instead of 1.75 turns because fuel is flowing some out of the transfer slot at idle). I am now running more on the transfer slot at idle instead of just on the idle port which for me helps. This also has the added affect of allowing me to open the throttles more during cruise, so I get more off of the transfer slot and more on the primary booster circuit at cruise. This has allowed me to have a leaner and more flat curve from cruise up to WOT. For some reason with the holes in the throttle blades, the transfer slot and booster circuit were both flowing fuel at cruise conditions which made for a rich condition where as idle and booster circuits were the correct AFR. I could never really fix this, so by installing solid throttle blades, I pushed the issue more towards idle where I could control the AFR by further leaning out the idle circuit.

Now I have mid 13s at cruise, with mid 13s at idle, 14s on the primary only, high 13s on the primaries with PV, and mid 12s at WOT. It is pretty decent. My fuel economy is around 13mpg at cruise if I can stand not rolling into the secondaries on a give tank of gas. The car has plenty of pickup for normal driving without hitting the back barrels, but it is hard for an acceleration junky to stay off the right pedal for 160 miles or so .

kalli

cool :-) delighted it's good for you now. any chance of further closing the 4 mixture screws ... like another 1/8 turn each. might be in the mid 14s for cruise then (huuuuge difference in mpg at least it was for me). especially on motorways at 60-70 mph cruise

urban_cowboy

Possibly, but cannot change it much more. My motor really surges around when my LM2 reads upper 14s. I know economy tunes run into the 15s, but man this 383 really hates it. You really notice the surging at cruise but for some reason when accelerating you only notice slightly less pin back in the seat feeling. At any rate, that is why I shoot for mid to high 13s with this motor. I am already better fuel economy than I was with my out of the box 750HP and I now have a bigger carb.