dellman83Z

iTrader: (9)

I got a 383 with a 4150hp mech sec carb. I needed to lean it out after my tranny change because it was now at like 12.8 afr cruising down the freeway. Current jetting is 73/82. With that change, its at 13.7. The problem I now have is that as I slowly increase the rpm, the leaner it gets, like up to 15-16 afr before the secondaries kick in. When they start to work, the afr drops to 13 and it did not do that before. I am wondering before I do this, but would it work if I jetted the primaries back up to 76 and drilled 3/16 holes in the plates.

pancherj

Is there a power valve on the secondary side? If there is a power valve on the secondaries, your jet spread is pretty wide.

Regardless, O2 sensors can be fun, but they can also provide too much information. Give the car what it wants. Under certain circumstances, a real lean AFR is fine. How does the car act as it leans out? Why did the change in transmissions affect the AFR?

I wouldn't go drilling holes in the throttle blades to try to lean out the engine at cruise (if you go to bigger jets). The first think I would do is hook a vacuum gage to the carb that you can read from inside the car. Now, drive around and take note of vacuum reading, AFR and RPM's. Log some of this data and get back to us.

dellman83Z

iTrader: (9)

There's no PV on the sec side. As far as why the afr changed, I believe its because of the 1000 rpm change by going back to an OD trans. Tomorrow, I think I will have time to log some data and report back.

865sp

whats your vacuum reading , you power valve in the front my be to small and not opening when it needs to? , and what is the size , 750 ,800 you may have lean out the front too much.

dellman83Z

iTrader: (9)

I figured out my lean issue for the most part, I changed from a pink cam to a orange cam and made sure the arms were adjusted right. It still has somewhat of a spike, but nearly as bad as it was. The other issue I have now is this. I have the idle transition slots on the primary side open to .025 and the sec side are closed to get it to idle nice. When I try to get the best vacuum with the idle screws, I can get up to 9 inches at 1100, but in gear, about 3 or less and wants to die because its leaned out too far. However, part throttle cruising afr is around 13.5 average. If I richen the idle screws by a quarter turn or so, it will idle much better in gear with 4-5 vacuum, but part throttle afr is real rich at 12-12.5 average. My pv is a 2.5 now. If I were to up my to a 4 or a 5, would that allow for maybe some fuel to come through and richen it at idle so I can back lean back out the idle screws to correct my part throtlle afr and also help my wot lean condition? The other idea is to close the secondaries a little more and open the primaries an equal amount to expose more of the transition slot letting more fuel in at idle, but would that be enough?

pancherj

The cams and pumps are just to cover the "hole" in the fuel curve when you open the throttle aggressively. The pump shot is quick and over fast. It has no impact on cruising AFR at all. To set the idle, I like to remove the carb and set the primaries so that the transition slot is roughly shaped like a square. Then, I take the secondary screw and flip it over so you can adjust with the carb on the car. Then, I see how many turns it takes for the seondary screw to make the transition slot a tiny square (Identical to the primary). Keep that number in mind and then set the secondary back to zero and bolt the carb on. Use the SECONDARY screw to adjust the idle speed and use a vacuum gage to set the idle mixture screws. You will need to go back and forth until it is as good as it will get. Make sure you don't open the secondary more the the number of turns it took to make the transition slot look "square". After it is all said and done, you can try to even the primary and secondary openings.

Need to know more about your combo...cylinder heads, camshaft, intake, timing curve, exhaust. Maybe someone will have a similar combo and can give you better direction. If you have a pretty big cam with lots of overlap, I would totally ignore anything your O2 sensor is saying at idle.

865sp

what is your timing at , and what type of cam are you running, if you open up the transition slot too much it will pull gas ,and make the air fuel screws useless

dellman83Z

iTrader: (9)

I feel like a fool for not thinking about just flipping over that screw, I have had the carb a bunch of times playing with it and never thought of it. what I have are dart pro1 200cc heads, air gap intake, 10.7/1 compression, comp roller cam 242/248 .54/.56 110 lsa. Timing is at 17 initial, 36 with mechanical all in at 2800 and 46 total with vacuum advance. I dont look at afr at idle because I know its not right because of the cam. I will try zeroing out the secondary and increasing it to get the idle correct. As far as the pv, should I go higher or leave it alone for now? Thanks for the help, much appreciated.

865sp

redo the dis curve so you can set the initial timing around 20-24 degrees or until it hard to start then go back , 36 at 3000 total and crank down the vacuum can or leave it unhook, this will idle the car up some so you can adjust it more with the air fuel mix screws and use you secondary screw to adjust some also, quick fuel make a nice flip over kit if you need it,if this doesn't work you need to drill some holes in the plates , and you might try a 1.5 the lightest pv

pancherj

I agree with upping the initial to 20 or so and limiting the total so it is around 36. However, I would say you need MORE vacuum advance. My setup is very similar to yours. My car likes 52* at idle/light cruise with the vacuum can hooked up (even with 48*, there is a noticeable difference in how my car idles and behaves at a light cruise).

After this, you may need to look at restricting your IAB's to allow less fuel into the idle circuit. You can test this by using a small piece of wire to restrict the passage (you need to take the metering block off). If the test moves you in the right direction, you will need to make the change permanent.

dellman83Z

iTrader: (9)

Sorry its been a while, been too busy lately to mess around with it. The best I could do for timing recurve was 19 initial and 36 total with this pro billet dizzy. Found out that my other dizzy had way too much end play and was messing with the timing and got the pro billet. Now cruising, the afr is around 14, which is fine, but now the lean surge is back with a vengeance. If I ease into the throttle slowly til the secondaries open, its fine, but if i mash it, it leans out bad, almost dies, then catches up. I would guess maybe play with the acceleator pump, going to a blue or green or a bigger squirter, say a 33 or 35 from the 31

pancherj

Certainly sounds like an accelerator pump issue. First, make sure that there is no play in the arm (car off). With the slightest movement of the throttle, you should get a squirt out of the pump circuit. If that is okay, then step up to 35 squirters and the blue pump cams (start in the #1 hole...if that doesn't work, then move it to the #2 hole).