How do you measure a weber carb jet size?

[sfoster13]

Chasing a popping and spitting problem and want to measure the jets. How do I take the measurement? Is it the diameter of the cylinder before the tapered tip?

[GaryR]

Look here, but I would first be sure the timing is spot on and that there are no vacuum leaks from old bushings on the throttle shafts.. and clean all the jets (including idle) if you are removing them, an ultrasonic cleaner works best.

http://www.racetep.com/webjettune.html

[jkh2cpu]

The jet sizes are stamped on the jets. Popping and spitting may be jets, and I'd start with the idle jets. Pull one out, get a magnifying glass, and see what you have. I'd guess the jets are OK, but you have clogged passages.

These cars are highly tuned, and if something gets out of whack you may have to run down a number of things.

I see that you have a 1971T, which came with Zenith carbs. Better tell us how long you've had the car, did the car ever run right since you had it, engine mods and type of carb.

[sfoster13]

thanks, yes I'm going down the check list before attacking the carbs. I have several things to do first on ignition before I get to the carbs, just want to know how to check the jet sizes. Carbs are very recently rebuilt by someone else. I think I actually have a couple possible issues. I have backfiring in the exhaust and popping/spitting in the carbs. Replacing the distributor from Marelli to Bosch, will set the timing, check fuel pressure, look for exhaust leaks, etc. I suspect ignition.

[BoxsterGT]

The numbers correspond to metric drill sizes, so you can use the drills to measure the jet diameters.

Some jets get drilled out so their stamps are wrong.

Len