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 LARGE Main Air Bleeds 
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Joined: Tue Aug 23, 2016 10:38 am
Posts: 84
So I picked up 2 carbs from my buddies on friday. One is a number 17057204 the second is a 17058222. I tore them both apart today and measured them. I will post all the measurements later but the biggest thing I noticed is the main air bleed size.

The both of these carbs had main air bleeds in both the lid and in the bore. Both of them measured approx .120 for both the lid and the bore main air bleed. The jetting for both is 77 with a 52 rod. In both cases the rods were the .026 tip diam rods instead of the .036 tips others have.

If you are following at home. He who shall not be named mentions them right in the middle of the "stage xyz" section of his book on 112 and roe mentions them as well.

So being far from an expert, what should I do? I assume the large air bleeds delay the main circuit operation so it come in later. Of course it will be leaner but isn't that why it has a large jet? Will this allow it to be leaner at cruise and richer under power?

Can I achieve the results I desire with out starting over by drilling and tapping the holes and installing screws with the smaller orifices?

Sun Sep 11, 2016 9:47 pm

Joined: Tue May 06, 2014 5:34 pm
Posts: 45
Those are very good carbs in my opinion. I've set up quite a few of those. Reducing the diameter of those large bleeds from .120 to between .046-.070. I reduce the size using old down channel restriction "cups", removing them using .110" drill bits.

Once you have those main air bleeds reduced, a good starting point is a 72 jet with a .043-.044 metering rod. The .026 metering rod tip IS the most popular. The .036 is for single main air bleed carbs ONLY.

Also don't forget to set-up the idle system using Tuner's tips. I've used his recipes many times to date and always get awesome results.

hope this helps.

Mon Sep 12, 2016 6:39 am

Joined: Fri Oct 23, 2015 8:43 am
Posts: 33
Those large air bleeds are common in late-70s Chevy carbs. Actually, I think they started in 1970, as I had a 7029202 with small bleeds, and a 7040202 with large bleeds - same application, one year apart. Not sure why they went to the large air bleed with a large main jet in the 1970s, as many BOP applications seemed to keep the smaller bleeds.

Mon Sep 12, 2016 8:42 am
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Joined: Fri Feb 08, 2013 2:37 pm
Posts: 1744
frank350 has the plan. 8)

Mon Sep 12, 2016 1:23 pm

Joined: Tue Aug 23, 2016 10:38 am
Posts: 84
That is the plan, I posted all the specs in a new thread.

Mon Sep 12, 2016 1:25 pm
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