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Problems with Weber jets

1072 Views 3 Replies 2 Participants Last post by  Gordon Raymond
One of the advantages of using Webers is that everything is built to a tight tolerance and you don't have to worry about new parts being correct - at least that used to be the case.

I wasted 2 hours this morning due to lousy aftermarket jets. I do timed WOT runs in the tuning of my motor - there are details in my "79 Spider on the dyno" thread. Yesterday I did a series of runs with different main jets. It was clear that 150 worked best and that run was with 170 AC's and the AFR was a bit too low. So today I ran with 150 mains and 180 and 200 AC's (I don't have a set of 190's). The afr was richer with the 180's today than it was with the 170's yesterday - Whiskey Tango Foxtrot? For some reason I have 8 150 MJ's and they are all in the same container. The AFR curves looked like the main jets were different so I measured them all. four were 1.5mm as they should be and four were about 1.43, in other words they are smaller than my 145's. Who knows what combination I have had in my Webers when I have been doing this testing. I talked to Richard Jemison and he has run into the same problem. He has a set of precision, miniature drill bits and he measures every jet before he uses it. It is a pity that some folks selling "weber" jets are pushing junk.
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With my own Weber restorations, I use a set of Weber plug gauges to check ALL jets. Often jets have been drilled, or soldered up and drilled over the years, and are NOT what they are marked. Reworked jets are tossed to avoid sometimes serious issues, or problems like yours. I also check all my new jets before installation. I too have found some new jets that measure other than as marked.
I didn't know about the jet gauges. Just bought a set on ebay.
They can be any brand. Check cheaper ones with a good michrometer, high $, no worry.
Check all your jets as you pick them up. Set aside small ones. Those can be re-drilled with tiny carbide jet drills and a pin hand vice. Any torque will break those carbide drills for smaller jets like the #35 pump jets.
They must be as marked or they are recycleable brass.
From my experience.
( At the track, I did solder and re-drill. I don't do this anymore after I burned a hole through a piston many years ago using a mis-marked jet.)
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