Did the search and went thru 17 pages to no availe. Ford F.E.-390 -600 Holley Question is I am now close to being correct 6 sizes larger than stock on primarys. Its been suggested to me that going more than 5 steps means using a different carb due to the metering circuit wont handle any jets that are greater than the 5 steps above stock. Any truth to this line of thinking. As I said-I am close but would like to go another 2 steps and see what happens on plug color. What say ye !!! Oldmics
Today's gas does "Color UP" the same as old gas and can be very misleading to use that method for jetting. Much better way would be to buy an inexpensive A/F meter and get a real time reading
The two previous posters are both correct! But depending on the tune of your 390, I would suggest you might be able to use a bit more carburetor. I have TWO 625's on my 390 on the street, and it is not too much. Jon.
I just use the hand choke slightly, to see if it adds or loses power at low to midrange rpm with a moderate load. It's good enough for most oldies I worked on.
I"m attempting to correct hiway speed surging and get a correct color on my plugs. I"m just curious to know if there is any truth to going greater than 5 jet sizes upwards is too much for the original metering circuit to handle? Thanks for all the answers. Oldmics
You have gone up 6 sizes on the mains and you have a part-throttle lean surge at highway speeds?? Something (other than main jets) aint right...
I had the same problem with a 80457 ! Part throttle lean is never going to get fixed with jets.... I had to drill the idle circuit restriction in the metering block. mine was approx .022 thou. drilled it out to .028>> surge gone ! Dave
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