Idles extremely rough without choke

['66U14]

Hey y'all,

Just put a rebuilt Holley 1946 carburetor on my '66 (170 straight six) to replace the Autolite 1100. Revved up it runs great, not rough or shaky at all. When it drops back down to idle, it runs rough as heck, really shaky and sounds like it's about to stall any second. When I close the choke about 3/4 of the way, the RPMs come up and it runs smooth as can be.

Any ideas/ suggestions?

Thanks y'all

 

[Rustytruck]

So what happens when you put the choke on. the idle position raises the idle mechanically and the choke raises the fuel to air ratio by blocking air. so to reverse this process look for a vacuum leak. missing hoses, ruptured diaphragms to the vacuum system or wrong or improperly carb gasket. if those are found good then check that the base idle setting with the linkage is set up high enough and and the mixture screw is doing its job. After that i would check the float level if it isn't set properly your idle quality can get very iffy.

 

[DJs74]

I too would suspect a vacuum leak, maybe base to intake... Cracked hose... Maybe carburetor internal. What level of rebuild? Could be something related to the rebuild?

If you have some carburetor cleaning spray, you can shoot it around different places to help identify a vacuum leak ( like around the base gasket, etc). The vapor from the spray basically sucks into the intake and burns and the idle will speed up momentarily ----- BE CAREFUL AND WATCH YOUR EYES AND FACE!!!!

DJs74

 

['66U14]

I bought the carb off ebay, from what I gathered in the description it was rebuilt by Holley and used for testing.

No vacuum leaks that I can tell, the truck idled fine on the Autolite 1100, I replaced it because the fuel inlet threads were stripped and leaking gas. Gasket around the base is fine too.