Im having a difficult time finding Motorcraft main jets, in the "old days" we used to drill out jets. I have one spare pair of jets, they are #54s just like what was in this unit (in a 302 with a rebuilt , new to me, carb) I drilled the #54s out with #52 bit, it seems to be somewhat better. First of all, can anyone tell me what # jets should be in a 302, 2bbl, ???I was told has mild cam (not sure if its true).

Second, anyone have a conversion chart, or just a good handle on what drill size = what jet size? if a #54 jet is the same as a #54 bit, (and it is) then when I drilled it with a #52 drill bit which is bigger, did I make it a #52? or a #56? ....is a #52 jet smaller than a #54? I am thinking about drilling one more size to a #50 bit, is this crazy too big? or is it reasonable that it may need this much fuel, it still seems starved, float level is good, vacuum is good, and drilling to a #52 did help a but... HELP!!

 

The bigger the number on the jet the more fuel you get. As far as the drill bits iam not sure, lol stupid me. When does it seemed starved. All the time or during accellration or what? I would think that no bigger than a #60 would be pletty of fuel for a 302. Are you running headers and good mufflers to let the engine breath better then maybe you could stand a bit more fuel. Dont know probally just have to keep expermenting. I have bought jets for holly 600cfm carbs and put them in Ford 2-barrells before, so you might check the local parts store for them.

 

Every book I have seen on carbs, recommends NOT drilling jets because the jets are sized by FLOW not diameter of hole. The jet number is larger as the hole increases, but they are not directly correlated. I agree with LMM on buying some Holley jets, start with about 56 or so and experiment from there.

 

What is the difference between Holly and Motorcraft jet size/number?

I understand that they use different systems. Is there a conversion chart, or even a formula? Somewhere someone said that one was based on drill bit size (true?) and the other was based on flow/cross section.

Little cornfused...

Kevin

 

The jet sizes are based on flow. They can not be drilled out and flow correctly for a given "size". The tiny things like the profile of the edge of the hole on both entry and exit affects flow greatly. You can't control those things with a drill bit.

 

I ran a wide band F/A gauge ended up between two sizes of jets, one number too lean, other too rich what I used was small tapered clock bushing reamers. Ream, take notes and test drive.
Drilling out a jet can result in less flow as the length of the restriction is increased due to the taper at each end of the jet.
By shortening the restriction length alone flow increases. You can have the same restriction size for more than one jet number.
I recall on Holley jets the flow increase was 3% for every jet number increase.

 

Don't want to hijack this thread. Simple question: What is thestandard size jet in a holley 600 cfm 4150/4160?

I want to go a size or two larger.

 

Usually a 600 Holley will have about 66 jets in them.
The 4180's have 62's.

 

btw, these guys have motorcraft jets. i've ordered some from them in the past to play with various sizes...

http://www.carburetion.com/ford2v.htm

 

When you re-jet a holley, do you replace both the primary and secondary or just the primary. Do you need new gaskets for the metering plate and float bowl each time you go in or can the old gaskets be reused? My carb is a 1 yr old 4150.

 

not neccesarily need to rejet both it depends on where you need to increase or decrease the mixture. If your running fine at part throttle and rich at full throttle then you would only switch the secondary jets. and it goes from there. As to the gaskets if they have been on there a long time without being disturbed then yeah you probably need to get new gaskets if they are fairly fresh gaskets in there then most of the time you don't need to replace them, and most of the ones you buy now are a non stick type made just for the ability to survive several jet changes without having to be replaced.