Good advice all.
Pretty much everyone here's got you in ball park, so well done.
westu37, What state are ya in?
if you are in one of the 33 I/M Inspection/Maintenance emission States, you can do a one point check at load on the test machine, and they'll give ya info so you'll
know.
Yeah, I'm with all that conservative change stuff, but past precedence, and a LOT of it says Go Ritchie Ritch. You can dial it back with a 65F later
if you have to.
Lean pinking is not aways noticable, and the Clay Smith cam is a faIrly intense cam for just a 1-BBL. Later on, you can dial it in closer.
Evidence...
http://www.econoline.org/carburetor.php?s=replaced_by
50 is the 1963 hi altitude Econoline Falcon 144 jet, before they started stamping them with F's and I think they had already changed from the Holley thread. Not a 170 jet, but a too lean 144 jet. Wouldn't use it even to redrill.
Point 1 is that a 50 is a wrong jet, its an above sea level 144 jet, bad option for what you are planning on doing with your 200. I think we agree if we look at the site above.
http://www.ford-trucks.com/forums/90881 ... stion.html
67F was Ak Millers jet size for the 1.290 C7 AZ 9510-AA manual Autolie 1101. Factory selection for that carb was 69F/67F/65F steps at altitudes. In his two Hot Rod articles, he never changed it from the size he whent to in his 1.10. That size ended up fueling 76 to 100 rear wheel hp, which ended up being 11 to 35 hp increase with other periferals (later on, headers, cam, valve spring work).
So right away, a 67F in a 1.100
without a cam gave 11 more rear wheel hp more.
Ak drilled the 62F jet to get a 67 thou jet size, and a drilled to 67 thou jet won't flow as well as a factory 67F jet, as they have a chamfer, surface prep, and controll flow rate testing. Ak knew that, so suggested a 65F.
So
Point 2, I'm with David
CZLN6. That sounds prudent.
Back ground to jets from that article. A thermactor sometimes requires about 8% more jet flow, 3 sizes up in some cases, but not all, because air is being added. Ak said nominal Jet sizes are usually .003 richer on such units, thats means an 0.067 "67F" should become an 0.070 "70F" jet size. So you can see how the fiddling can go. The Econoline site doesn't corroborate that, jets sizes go up one call number with 240 and 200's with thermactor.
What I'm saying, is it aint 1967....
Thing is, modern unleaded Oxygenated fuels (with added Benzene, Tolulene, both thinners and light aromatic hydrocarbons) lean the engine off, so richening it is even more of a positive idea. Stoichometeric ratio swings from 14.7 to 15.1 with new gasoline blends, so you'd be advised to get jets that flow 3% more fuel to aid richness, a jet size just for a start. 66F. Ak's car eventully went to Hi Test gas.
Point 3, In 1967, emissions, fuel type was a beneficial small change, but performance jetting changes due to cams are often HUGE if the engine is larley stock.
So flip forward to a cammed up, modern fueled but fairly stock 200 I6
A cam like that means you need more jet.
JackFish runs, IIRC, a 65H in his 78 Fairmont Wagon, a 1.30" Holley 1946 with that cam up from 61H stock, up 3 jet sizes.
An Ford xxF jet is always 4 call size steps below an Holley xxH jet in the Holley jet sizes from 40 to 71. Above that, the Ford xxF jets are way smaller in number, and very different.
Point 4. Based on all this, at the very least, you wanna step it up to a larger than 65F for safety a
heck of a lot more than just what Ak suggested for what was a non cammed up 200 in the first stages.
I ran a 71H jet in my initally stock cammed 1981 3.3 with 1.30" 1946c Holley on High aromatics gasoline., a 67F on a 1.10 isn't too much.
Q. How much horsepower do two 50F jets make on a 1966 C code 289 Mustang 2-BBL 1.14 carb?
A 130 rwhp.
Divide it in half, you get just 65 rwhp, which is way below the required results of a cam upgraded I6. 289/2= 144 1-bbl jetting.
It'll lean out like this graph
Each 2 decrease in jet size, i.e. from 51 to 49, will raise your cruise AFR by a full 1.0. Main jets have no effect at idle and not much in the transition to cruise. For our {289 C code 66 Mustang} coupe with a 2.80 rear, it takes 50 MPH to reach 'cruise' where the AFR becomes nearly constant with speed.
What you have to move to is like THINKING you have a 2-bbl 400 Ford V8...
divided in half...a 1-bbl 200!.
So before I recomended 67F, I asked myself,
Q. "When does one add two 67F jets to an normal 56F jetted 1.21 351W, 351C, 351M, or 400 Ford?"
A. "When
just upgrading the camshaft to a 265 at lash/ 215 at 50 thou and getting a better timing chain gear set".......stock cams on those, like our 200's, were just were 256 degrees with about 190 at 50 thou with more on the exhaust on some versions; like the I6, they have a really poor gear set which retards and scatters the timing with age.
but when cammed up with something like your specs, they
really need much more jetting, and 67F's on that engine aren't too much even with stock intake, carb, and exhaust manifolds.
Same with yours. Anyway, your car, your cam, youre on the right track. 72F is too big, 65F too small, 67F, ball park.
Best advice?
Wide band O2 sensors which give you air fuel ratios are just fine if you have the time and money, but auto engineers went to C02 readings many years ago to simplify it, and the black CO to AIR fuel ratio in terchange is the easiest system to tune a jet to if the cars under load.
These are the is the graphs...
Toyotas later graph
Black line for CO on the right axis
Crytons graph is the blue line for CO
At 15.1 to 13:1, CO % via the sniffer test is VERY accurate as it drops like a fly in the frost....
Soooo
You could just drill the jet like Ak did, check your fuel air under 25 mph load at an I/M test station, and stop drilling when you get to a %co under load of about 2%, which is a about 13.8 parts or air to one of fuel. 14.7 or 15.1 (..75 to 0.60% CO) is too lean under load for our cars. 4.5 to 5% CO is ideal wide open throttle 12.5:1 one.
This is how we tuned our old propane vehciles for safety, although that was done by allen key and screw, not jet change
and its how Ak Miller suggested it be done in the Impco propane Tech Service Bulletins from the late 70's to early 80's.
Modern ways aren't always the easiest. Every garage has access to tuning gear, rather than pay for individual equipment, you use the I/.M stuff
