carb tuners, step in ......

[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...