IDF’s/ Jet size

[MIGHTY 8]

Hello all,
Ordered some Main Jets. Using a German made jet gauge tool, I measured and can see some jet’s stamped number matches the gauge, while others don’t match.
Common problem?

Trust the gauge and use different stamped jets but all matched to the tool?

Thank you!

[18Fiatsandcounting]

How big is the difference? If the jet is stamped as 142 and you measure 140, that's probably just acceptable variations.

Personally, I would trust the gauge. I have drilled out some jets to get the jet size I needed, using a machine shop with precision metric bits. So I'm guessing others have done this as well. If you are buying the jets new from a supplier and the sizes don't match the stamping, I would call the vendor. It's possible they got the jets mixed up.

I also recall reading something about "effective" jet size, where the hole was drilled to provide flow characteristics corresponding to what was stamped on the jet, but not necessarily the actual static hole size. I don't know if this in BS or a real factor.

-Bryan

[MIGHTY 8]

How big is the difference? If the jet is stamped as 142 and you measure 140, that's probably just acceptable variations.

Personally, I would trust the gauge. I have drilled out some jets to get the jet size I needed, using a machine shop with precision metric bits. So I'm guessing others have done this as well. If you are buying the jets new from a supplier and the sizes don't match the stamping, I would call the vendor. It's possible they got the jets mixed up.

I also recall reading something about "effective" jet size, where the hole was drilled to provide flow characteristics corresponding to what was stamped on the jet, but not necessarily the actual static hole size. I don't know if this in BS or a real factor.

-Bryan

Thank you for the response.
I did reach out to the vendor. Basically told they sell "thousands of these jets, and no one else has made claims to their sizing."
In my case it was one size off (I.e, a stamped 140 gauged out to 130, while some stamped 130’s gauged out to 120.)
For what it’s worth, I gauged my air corrector jets, and they all gauged to be accurate to their stamped size.
Spoke with some folks, and it doesn’t appear that a lot of people measure/ gauge these things anyway…

Oh well. Just learning as I go along here

[18Fiatsandcounting]

If your air corrector jets are correct using your gauge, then my guess is that your gauge is accurate. I don't really have a feel for how accurate the hole diameters are in the main jets, but it wouldn't surprise me to hear that some are not very accurate as you have discovered.

I have a number of jets, and I visually inspect the hole of a new (potentially wrong) jet against the known ones. As examples, differences of 1.40 to 1.50 are easy to see visually, although distinguishing 1.40 from 1.45 can be challenging. Holding them up against a bright sky as a backlight helps.

-Bryan