carb tuners, step in ......

[LX2NV]

ok fellas i'll give a quick rundown.... i know there's some helpful guys on here with similar setup's, i'm pulling my hair ! .......

359 windsor, 11.1 compression
lightly ported canfield 195's
C.I. cam, .600/.592, 232/245, on a 113.5
victor jr. intake, proform race 750
bbk lt's, 2.5 h, with dumps
4.10, with a tko


i'm using a innovate lm1 wideband, i can maintain about 13.2-13.9 idle (950 rpm's) and cruise, about 12.2-12.4 wot, still fat but runs out great. when i get to the track i'll do some more tuning on the secondary side of things. there's one spot just above idle on cruise that will lean spike 14.9-15.5 occasionally, probablly like 2-5% throttle. i have been fighting this spot forever. it doesn't do it all the time and it's not bad when it does it, easily overcome by adding a "hair" of throttle. i'm running 16 degrees of initial timing with 30 total, all in by 2400 and starts advancing down low around 1000 (just above idle). any more timing it pings, any quicker advance, it pings. 11"-12" vac. at idle.


current carb specs...

primary jetting 72
secondary jetting 81 (jet extensions)
IR .033" all 4
IAB 73 all 4
MAB 26 all 4
idle mix screws all about 3/4 from seated
6.5 power valve, rear blocked
transition slots F .030"-.035", R .020"-.025"
i drilled 2 3/32" (.093) holes in front blades to get the T slot smaller
boosters comming in about 2050.
fuel level in bowls *just* trickles out

it's just that occasional lean pocket just when i move the butterflys from fully closed at a low rpm cruise under 2000 rpm's. typically right after i get on it. anything above 2100-2200 it goes away. this is the only issue keeping my car from feeling like efi. anyone have any suggestions or critique my setup ?

[Rodeheaver's]

i bet that a larger squirter will fix it..

[torqueboxer]

what acc pump cams/ position are you running?

[LX2NV]

i was waiting for both of you two specifically to step in.... dave too (thebreeze72).

squirters...

F pink cam 1st setting 35 nozzle
R pink cam 1st setting 37 nozzle

tip in seems to be good everywhere...? it's more of a issue of holding the pedal steady... very lightly is when it will do it.

[LX2NV]

what acc pump cams/ position are you running?

me and you got close combos. close cars too...


here's what we're working on......

[Rodeheaver's]

edit...maybe try a 5.5 power valve..

[torqueboxer]

our cars seem to be the same color too!! and the same wheels, and the same hood, deep jewel emerald green? i have an old school holley "pre 1975" and mine will do the same thing just on tip in throttle, just on the transition circuit before it gets to the jets, you might have luck with moving the acc pump cam to #2 position(make sure to loosen the spring/bolt assembly so that there is no slack in the acc pump arm. the acc pump is the main thing in a carb that will "pad" the change from one metering circuit to the next while the throttle is moving through its arc.

have someone look at the carb while you press the throttle down "engine off" and ask him to look at the shooters. it should be making a STRONG stream of fuel at that throttle position play the pump cams/positions till its squirting heaviest at that position. a small increase of the idle mixture screws will also help to get rid of a lean off idle situation

[yeahloh95]

off topic just alittle but i'm glad you guys are here i'm building a similar combo for my coupe

[LX2NV]

thanks for the input guys. keep it comming ! yes, the car is deep jeweled green, street lethal just painted the hood for me (excellent work ). i don't believe the problem to be a squirter, cam issue... but it could be ? it seems i could make the car do it for as long as i'd like. the conditions have to be just right for the problem to surface. i will continue making fine adjustments to the t-slot and air screws and float levels, fuel press. also. the sizing of the air bleeds intrests me as well. i kinda modeled it after a 70's d.p. this is a minor issue that i would love to clean up just because i personally know so many carb haters. i would call the area in need the upper end of the idle/transition circuit. if i richen up my idle mix screws my a/f starts falling in the mid 12's at idle, that's fat and teary...

[LX2NV]

well, i played with the balance of the T slot secondary and primary and got the car driving flawlessly. now, i have a fat cruise (12.2-12.6) and a fat idle (12.7-13.1). i'm afraid to screw with it , but the low rpm cruise/transition is excellent now.


i dropped the secondarys down to 80's. a/f is nice and steady 12.7-12.9 under WOT, a little cleaner than before, i can really feel it.

the pump cams do need some tuning. i will have to buy the cam kit and do some playing around.... nothing i can feel, but see on the wideband. overall it just took some very minor adjustments to the t slots and float levels. i guess this motor is just more touchy than others i have played with, it's very sensitive. i don't know weather or not to try and thin out the cruise now ? the transition is so good, but on the other hand i'm in the territory of wasting fuel.......

[LX2NV]

can i have more details on your a/f ratio ? also some more details on ignition timing (base+adv.+total) ? where were all of your peak numbers achieved ? i think my car should be putting down numbers close to what yours does, but i know it's not.....

[Rodeheaver's]

what size is the carb? it almost sounds like a low fuel signal issue.. what are you doing to the transision slots as far as modifying?

[LX2NV]

what size is the carb? it almost sounds like a low fuel signal issue.. what are you doing to the transision slots as far as modifying?

it's a proform race 750 AKA a quickuel Q series. mechanical secondaries. yes, i guess it would be a low signal with my cam and the big open plenmum intake, not to mention my modest timing... this is what i'm trying to overcome.

i'm not really "modifying" my T slots, just trying to find the right balance of F to R.... you know what i mean, once you get close a little change can have a big effect. my stumble is gone, but i'm left on the fat side of things now in my idle/transition circuit. i know if i lean my air screws at all the stumble will return. if i make my IFR any smaller, the stumble will return. if i go any higher IAB, the stumble returns. i'm considering filling in some of the t slot with epoxy, this thing has huge (long) slots. too long really, on the primary with the set screw backed all the way off the primary is about .018-.020... that's not right.


let me just say that this thing currently has efi manners, it's just the wideband is telling me it's fat, too fat down there. i was told that anything richer than 12.2 and you're wasting fuel. that's why i'm concerned with my cruise around that number ? i'm just not sure on how to go about correcting it without the lean spot comming back...?

[torqueboxer]

I keep my idle speed at 1000rpm hot and engine temp about 160-170d at full temp.
Im at about 13.7-13.4 idle

cruise is right about 12.5 to 12.7 cruise on a warm day. when it gets cold out below 50d with my settings its go way lean in the 15's and start to miss and buck under low throttle position when cruising, pretty much what you are talking about. a 1/8th turn out of the idle screws will take care of it all the way down to the teens and twentys outside air( yes i will cruise my car on bright days in the middle of winter) at which point i will jet up two sizes on the primarys. My car never even gets into the fuel enrichment curcuit while just driving around(jets dont come on until 3500 steady cruise high vaccume). Dont be so hung up on the actual a/f numbers...they are just a rule of thumb

As for the timing im running the blue spacer, second from smallest, the small silver springs 18base and 36-38 total. all in by 2800. no detonation ever. one thing i did pay attention to was the quench when i put my mmotor together it has .036 which really helps with our poop 91 octane we get and my 11-1 compression. 250 deg@.050 duration helps too!!

last night we went to dyno aubele's road race car and we only had to jet one size up from my initial guess of 68/76 on his car it put down 345@6500 and 300ft lbs at 5300 that was on a stock short block, tfs heads, n-91 cam, vic jr intake, and a leftover 750 i had laying around at WOT his peak power came in at a 12.7-12.9 afr with a 13.9 idle AFR.

By the way my car usually gets about 16mpg on the trips to zeli, ebensburg, and keystone...as long as i keep below 2600rpm, after that and it starts to tickle the boosters and it goes to about 10 or less. Ive had the same plugs in my car for 2 years now still look like new

[LX2NV]

very helpful, thanks for taking the time to respond. my testing was done earlier in the week in the hot humid(80+deg)air, so i'm sure this is playing a role in my 12.2-12.6 cruise. i have a good cooling system, it never gets over 175. any more than 32 total and it will detonate. my quench is around .045", i should have made it tighter. im running the blue springs. the a/f is staying steady 12.4 (wot)-13.7 through the entire powerband. it runs good, no hesitation anywhere, i guess i should leave well enough alone and wait for some cooler dryer air and see what happens. and like you said don't be so hung up on the numbers. different engines like different things i guess...