I have a model No. O-1850-x carb and the Holley carb list shows the primary and secondary jets as 122-66 and 134-9, respectively. What are the jet sizes? 66 and 9? Is that in 1000's of an inch, which makes no sense. 1000's and 100's? My 77 F-150 4x4, (400, headers, Edlebrock intake) runs way, way too rich at idle and speed. I've adjusted the air mix screws with little improvement (I know that only affects idle). And have set the float correctly. The plugs are black and sooty. Runs great at speed (or used to), just too rich. I'm thinking of changing the primary jet size down. Any suggestions? Thinking of going 1 or 2 sizes down. Which is the next size down? One other thing, now it started back firing. I think I've blown out the power valve by messing with it.

 

refers to a specific (predrilled) jet size but the number alone doesn't help. I have a book at home that will tell what jet size is equivalent to the 134-9 metering plate. I think it is around a 62 jet size. I had a 4160 carb and converted to a 4150 model by replacing the metering plate with a metering block (which allows jet size changes). Holley sells these kits.

Reagrding running rich, have you checked the choke setting? If it does not pull open corrctly and open fully at the right time your plugs will be sooty.

 

When you replace the PV, you can add "blow out protection". Holley sells a kit to prvent blowing the PV from a backfire. All the new carbs have this built in already.

 

It's a manual choke. Is there a way to set a manual choke? Have been thinking of converting to an electric. Got the parts and going to go get my hands dirty. Thanks.

 

I looked up the info in my Holley book - the 134-9 metering plate is equivalent to a 67 jet. By the way, the jet size is the drill size (i.e. 67 jet = .067 drill bit).
Mike

 

Just finished rebuilding the carb and dropped down 3 jet sizes to a 63. Also changed the secondary (kick-down?) spring to a weaker spring because couldn't ever feel the secondary kick in. It had a fairly heavy "plain" spring in it. The Holley spring kit (with several springs of different colors) listed the plain spring, which matched the one in my carb, as kicking in at ~1,800 RPM. I dropped it down one to ~1,600 RPM.