Jet, Corrector, Holder drilling

[PaulProe]

A number of questions on the practice of drilling jets/holders/correctors

1. I have a number of jets I obtained from a friend who has, in the past, drilled jets till he found what he liked, then ordered a set of replacements at that size. The jets he lent me, I don't know if they've been drilled or not. Example is an idle jet market 55F10. But a .60 mm drill will go thru it with just a very slight drag. The drill shank actually measures .565mm. the $1000 question, is the jet actually a 55 or is it a 60?
2. Does anyone know the typical undersize amount a drill is from the hole it is supposed to drill. ie, if it is a .60mm drill, what should the bit shank actually measure? I know the drills will drill just slightly larger than the shank, but I don't know how much
3. Does everyone agree it is an acceptable practice to drill holders or correctors since they are passing air and not as flow critical as jets?
4. Is there a way to definitively tell if a jet has been drilled or not. Obviously, if it is marked 150 and it passes a 170 drill, but what about those that are just a few thousands oversize?

Thanks

Paul

[FWB]

Originally Posted by PaulProe

A number of questions on the practice of drilling jets/holders/correctors

1. I have a number of jets I obtained from a friend who has, in the past, drilled jets till he found what he liked, then ordered a set of replacements at that size. The jets he lent me, I don't know if they've been drilled or not. Example is an idle jet market 55F10. But a .60 mm drill will go thru it with just a very slight drag. The drill shank actually measures .565mm. the $1000 question, is the jet actually a 55 or is it a 60?
2. Does anyone know the typical undersize amount a drill is from the hole it is supposed to drill. ie, if it is a .60mm drill, what should the bit shank actually measure? I know the drills will drill just slightly larger than the shank, but I don't know how much
3. Does everyone agree it is an acceptable practice to drill holders or correctors since they are passing air and not as flow critical as jets?
4. Is there a way to definitively tell if a jet has been drilled or not. Obviously, if it is marked 150 and it passes a 170 drill, but what about those that are just a few thousands oversize?

Thanks

Paul

more to a jet than just its orifice size there are entry and exit differences.
personally any used jet that has been drilled, i would call trash

[FWB]

the ones i posted are holleys if you are referring to webers, that is above my pay grade.
still, i would call them trash if they were drilled out

[Rick Parker]

PaulProe:

The actual size listed on the various jets or air correctors is somewhat ambiguous. Unless a reamer is used to properly size them. The size may be slightly larger, however the recommendations, listings, and sizes are there for comparison and adjusting ratios between the air and fuel using charts that Weber published. You could totally eliminate the MM reference and go to a set of Numbered and Lettered drills and end up with a totally functioning carb. The amount that the drill would remove in excess is miniscual and you would be hard pressed to notice any difference with an OEM VS one carefully sized by hand with a pin vise and a set of drills.