Oh, I was wrong, there are those 26 Mikes Carbs Main Metering Jet sizes, plus others. The metering rods won't work with every one, but most 75 series rods will. There are some exceptions.
The best universal main jet kit reference is the 600 series Edelbrock 4-bbl main jets. They are marked with a three-digit part number that indicates the diameter of the metering orifice. Jet sizes starting with a 3 are smaller than 0.100 inch; jets beginning with a 4 are larger than 0.100 inch, so this 389 jet has an 0.089-inch orifice.:-
Main jets:
Size: Carter: Edelbrock:
.083 120-383 1422
.086 120-386 1423
.089 120-389 1424
.092 120-392 1425
.098 120-398 1427
.101 120-401 1429
.104 120-404 1430
.107 120-407 1431
.110 120-410 1432
.113 120-413 1433
.116 120-416 1434
I've underlines the 98 to 110 thou main jets, as one of these will likely be what you have now.
Mikes Carbs uses the common earlier Older Carter reference of
120-160 = .091",
120-166 = .0935",
120-155 = .096",
120-170 =.102,
120-161 =.104 etc
Reducing the annular radius exposed at a given vaccum point makes the carb leaner, so you will most likely be best measuring what you have, and then finding a valid other needle that is known to be leaner. Its easier to start lean, and then have it mechined back via a needle file if you can't get the right metering rod.
If that's not an option for you, then you will need to find the replacement Ford small six metering rod and main jet. Or just a metering rod at the very least. One company,
Black Hawk Engineering , does YH Turbo F85 JetFire and Corvair Monza YH reprofiles, the web info they have will help you arrive at the right air fuel ratio for the price of baselined air fuel ratio measurement. with you current set up.
I'm picking that you'll be able to find any Carter YFA metering rod to suit, and you'll then be able to use there annualr area charts to adjust the air fuel ratio.
Black Hawk Engineering do a reprofilr service for sub 94 thou jets
"Choose dimensions for a new rod
If you have measured air/fuel ratio numbers for cruise and power, you can adjust the flow areas proportionately. For example, if you have a power A/F ratio of 11 to 1 and you would like to have a ratio of 12 to 1, the ratio is 11 divided by 12 or .92. If your current power flow area is 300, multiply .92 times 300 equals 276. Look in the General tables for the jet size you are using and find the flow area closest to 276. Then read the corresponding metering rod diameter. Do the same type of calculations for the cruise step.
Our current manufacturing process is limited to diameters of .054 to .094".
If the metering rod you want falls outside of this range, you will have to choose another jet size to find a combination that works. The available jet sizes are .077, .080, .083, .086, .089, .092, .095, .098, .101, .104, .107, .110, .113, .116 and .119"
That then means tracking down a common junked Jeep 258, 2.5 liter I4, Ford 0HC 2.3, 170/200/250/240/300 jet. You'll get lucky enough form this...I'll help out, its just math. You'll just have to warm up your car up for 10 minutes, and get C02 readings or air fuel readings from a test station at Cruise and Power; as well, an IM test at load would be a good first start.
Then its just find and measure a jet that will lean the mixture off enough, and recheck it.
http://www.blackhawkengr.com/
http://www.blackhawkengr.com/Black%20Ha ... ustom.html
The way to work out the difference is from a known base on one of these charts with the same main metering jet.
http://www.blackhawkengr.com/General%20 ... Tables.pdf
You wont need the first 17 main jet sizes from Mikes Carbs, they are just 54 to 96 thou. Somewhere between 98 to 120 will be the possible, with 98 to 110 being the best options I'd say. One of which you may have right now.
Carter YF carbs begin to appear in 1967 on California emissions equipped engines.
By 1970 it was standard on 170's and 200's. They were rated at 150 CFM on 170 c.i. engines and 187 CFM on 200's. The YF carb was also used on the 250 engine from 1975 -79. The 250 version of the YF was rated at 195 CFM. It remained the "small six" carb until 1977 on the 200 and 1980 on the 250, and the permanant 240/300 carb from 1969 till the death of the 1-bbl F150 in 1987.
Some ballpark details from Big Sixes.
1979 Manual F150 Replacement from Ford for that year was nothing for Ford Dealer Main jet (no size diameter given) but it was part C8AZ-9533-A, and that pegs it as a C8 jet of 104 to 110, with 106 most likely.
Idle adjusting needle (assumed to be metering rod) D7PZ-9541-A (no sizes given)
For one 1979 Manual F150 4.9 Bix Six:-
Main jet is 0.1056 inches;
numbers on top face of brass main jet appear to be 120-410;
Brass metering rod number is numbered #75-2346 (which I can't find on the list)
Diameter of metering rod is 0.040 inches at tip going into main jet;
0.054 inches at second taper on metering rod,
0.815 inches on main shaft near top of rod (all measurements with digital caliper)
Other 1979 YFA carbs have been
Main Jet 0.107dia inside
numbers on top face of brass main jet appear to be 120-407;
Brass metering rod number is numbered #75-217
sic (which could only be a #75-2175 or 75-2176)
No accurate dimensions exist for a so called 217
The 75-2189 was a valid metering rod on that table well.
On a Jeep, a 120-166 main jet @ .0935" would use a 75-1570 metering rod for 65 net flywheel hp.
Form LZJW 98 to 110 are valid main jet sizes.
D2 prefix are all for 1972 engines;
the only D2 carb showing for a 72 300 has a main jet of .110",
all the rest (four) are for 240's,
three of which call for a .104" jet
and the fourth one is .101".
Stock, the C8 prefix show a main jet of .104".(69 240 [.104"] with a carb tag # C8UF-M)
Smallest Big Six YFA jet listed is .098" (one model only) and the biggest is .110
Try sourcing a replacement metering rod and 98 main jet from Mikes Carbs for carb tag 1969 240 F100 carb tag # C8UF-M:-
The common ones for a way too small 134 cubic inch I4 65 hp net Jeep are:-
Carter Main Jets
Main Metering Jet
120-155 = .096"
120-160 = .091"
120-166 = .0935"
But I'm pretty sure you won't need to change what is there at all...
These two posts help best.
motzingg":1z9he1oi said:
yep, its pretty simple. they are basic little carbs.
navigate to the link if the image doesn't display correctly:
http://oldcarmanualproject.com/manuals/ ... 19_jpg.jpg
i'm pretty sure its just a 'low speed jet' and a 'metering rod jet' but the 'metering rod' is also a tuning component, you might have a mis-matched metering rod (us motorcycle guys call them a 'needle') and jet.
here is the metering rod assembly.
If you buy a rebuild kit, they usually have that pic i attached printed out for you on a big sheet of paper, still might want to take photos of the stages of carb disassembly while you are doing it, however. Here is a picture i took from when i did mine.
THE FRENCHTOWN FLYER":1z9he1oi said:
Before changing jets I would try the metering rod adjustment. It has always fixed any YF mixture issues I've seen. The screw in the background raises and lowers the tapered rod in the jet. Raising it will fatten up the part throttle mixture without fattening up the WOT mixture, which I suspect is not too lean anyway. Plug readings at WOT mnust be taken after running the engine at WOT and not letting it come back down to idle while running or the WOT reading will be affected.
Modern plugs will tolerate a leaner mixture and may look white, even though the mixture is correct. This is especially noticeable on fuel injected engines.
My buddy John would always send his driver (aka his wife) down the track with a ratchet plug wrench and a spare plug. She would kill the engine at WOT, coast to a stop, change the plug in question, and bring the unsullied plug back to the pits for inspection. He was an absolute wizard at tuning Weber IR systems.
