1.01 289 autolite VS 0.98: jetting/ttuning? (250)

So, as the title suggests, i have modded my 250 to take an autolite 2v carb. (milled log to fit, no restrictive adapter) I'm lucky, and have 2 to use, one is off a 67 289, the other is from a (fairlane?) 260 V8. Both have been rebuilt and ultrasonically cleaned correctly ( by me)

I initially ran the 1.01 carb, and while it ran great, it also ran rich. as hell. made lots of power when the throttle was opened but idles rich, and just seemed to be dumping fuel. the carb is in great condition, the emulsion tubes are not cracked, etc. but I could NOT get it to lean down any at idle. checked float level, etc.



the other carb i put on out of somewhat desperation, also in perfect shape, and decided to try it but the caveat was the interchangeability of the jets with Holley ones, which are on the shelf at the local speed shop.

for clarity: motor is a 76 250, bottom end dead stock, shaved head ).070 some porting, comp cams 260H grind cam installed straight up, HEI ignition and 6-1 header.

so, the 289 carb had 54 mains, and i am truly unfamiliar with the emulsion setup on these, so not sure whats in there, aside from its stock. The other (260) one had 46 mains, and the rest stock. I feel liek im leaving a bit of meat on the bone with the 0.98 carb, but i did have to jet it up to Holley 50 mains to get the lean detonation out of the motor. going to jet up to 52's and try to dial it in even more. Motors running nice and in range with these, temp wise as well, sitting around 190-195 (prior it would climb to 208-ish on the highway at 2800-3k rpm)

my concern is more with mid-range. I figure, on the emulsion/spray assembly in the carb, there are 2 drilled orifices on the top of it that allow air to emulsify into the assembly. I speculate i can drill and tap these holes and use air jets to control the richness of the cab in this circuit.

who is familiar with this modification on the autolites, and any advice would be great. I also speculate i can do the reverse for the 1.01 and maybe lean it out a a bit to make it work if i need to. The carbs are close in size so i'm not opposed to leaving the .098 on.

also, i know the spray assemblies can PHYSICALLY be swapped, but didnt know about the pitfalls of doing so.

I know thats a lot, but im def curious as to how these can be tuned. Thanks.

I can help you, but i need A/F ratios crusing, WOT, idle & A/F during the transaction range, which is just after idle, but not cruising. Like driving around the neighborhood.
An Innovate wideband tester or a O2 sensor installed in the headpipe. Bill

i plan on doing that when the final exhaust gets run, right nw its sort of a crappy system on there, didnt want to weld the 02 bung ona pipe thats going to be replaced.

I can tune with an , i just want to know IF modifying the spray nozzle has been done w airjets, or if anybody has run the 1.01 and what the rough setup was. Im def curious to hear what your thoughts are on this. Im MUCH more familiar with motorcycle carbs, especially on 2 strokes. (lectrons, mikunis, pwk kehins, etc) and FI tuning.

Howdy M in SC:

FYI- the .98 Autolites were designed for '62 & '63 221 V8s, the 1.01s were designed with the '63 & '64 260 V8s in mind. However, with FoMoCo nothing is ever always, so, your carbs may or may not have come originally from the vehicles from which you retrieved them. Take a looks on the mounting foot of the base of each carb, under the accelerator pump rod, for a code stamping. That will give you a more accurate idea of what vehicle/engine the carb was originally designed for. Also, 2100s prior to '64 will be using Holley jets. Thats a big plus because Holley jets are so much more available. The internal design of the K cluster was specific to vehicle use and included variable such as vehicle weight, transmission, gearing (and market). While K clusters are interchangeable, codes stamped on the mounting base and uses are a bit of a mystery. K cluster designs have been changed in a running model year so even with the code internals are not predictable. The K cluster effects transition, idle and acceleration circuits. It includes the squirters, air bleeds and the emulsion tubes. So, knowing what you are starting with is a good start, but not a guarantee.

By carefully measuring the size of the squirter hole you may be able to mix and match to zero in on acceleration and transition a bit. High and low speed transitions take place in the emulsion tubes and the air bleeds. Air bleed holes are accessible but the emulsion tubes are less so.

While much of the function of the 2100 is built in, a great deal of tune-ability is available with choke function, low speed air screws, accelerator pump arms, main jets and power valves. The distributor initial and internal advance curves are also very important to carb tuning.

Bill, aka wsa111, is the guy for fine tuning these issues in a Holley 2300 and may be for the Autolite 2100 also. He is also a great source for distributor recurving. I'm sure hoping you will find more about your 2100s and share your insights with this forum. Keep it coming.

FYI- Holley power valves can be used in 2100s. The Power Valve Channel Restriction (PVCR) in each carb is a given, but can be modified by drilling or restricting.

Hope that this is helpful to you.

Adios, David

Thanks David, yes the Holley carb has orifices which are easy to change if you know what you are doing.
The Autolite also has the diameter of the idle tube & the idle air bleed.
But i need to know what you have as far as A/F readings before i can correct your problem.
Just changing main jets is only controls WOT & cruising ratio. Yes it affects the PVRC, but thats a different mod all by its self. Bill

great info guys. the jet change was primarily due to WOT and steady engine speeds issues, i think i have that sussed. I do know that the 1.01 did infact come off of a 67 comet with a 289, the car belongs to a friend of mine and i got the carb when we swapped on an afb and intake, and i do know the full history of that one.

However,the .98 was pulled from a 260 car.. but doesnt mean it was NOT a 221 carb somebody stuck on 40 years ago, it did come out of a yard.

I will stick with the 098 and go up on the mains a hair more, but the emulsion tubes (k cluster, learned a new phrase) will definately be looked into.

The powervalve is an interesting point, it does seem to be a bit rich on transition, i may try to tune with that as well. great stuff guys.

i have an exhaust leak to attend to, then will ge the system set up to read afr, (which i do have the gauge from summit) which IS the best way, i agree. Im trying to get it close by feel then really dial it in.

so far so good.. up to 52 mians and seems to be holding OK. im going to try 54's and see if thats ok.

ona side note, i have soem jets from th elocal u-pull it for my 'large' jet 2100, so maybe i can bracked it down and experiemnt with that as well don the road.

for the meantime im fighting a pretty nasty valvecover leak thats giving me fits.

HOwdy:

Is the valve cover a stock, FoMoCo cover? What kind/material is the VC gasket?

adios, David

You guys will never learn that just changing main jets & power valve & accelerator pump discharge nozzle will fix your condition.
Without what i asked for you are just guessing.
One you get your A/F sensor installed i will be glad to help you or fix your problem.

its ok.. i'll figure it out, im pretty adept at tuning, but was trying to at least get a baseline on this as I am more familiar with what i stated above.

I have changed the PV to open later (more vacuum required) and the mains are larger. the accel pump stroke is on the lowest setting as anything above that and its def rich, really good now, can cook up a tire froma dead standstill zero hesitation. I did retard the timing a hair and am at 32 degrees total, seems to be happy there. the issue i really had was wot and building heat. the richer pmains took care of that, i'll stay out of the nozzles for now.

when i eventiually get the new exhaust run, i am going to have my wideband on there and data log via throttle position and ambiaent air temps, and will adjust accordingly then. if, in fact, it IS lean in the mids, (or fat), i will install air jets on the k cluster and tune from there.


yes, the valve vcoever is afactory one. i think the P/O overtightened the pass side bolt near the front and cracked the housing. time to take off and investigate. thsi weekends lookign promising.

I did have a rubber gasket, hated it, got a cork one,. still leaking but only there and not as bad.