Thread size intake manifold vacuum port

Ronbo

Famous Member
High all. I have the 250 head and was wondering what the thread size is for the vacuum fitting that sits behind the carb pad. I have a fitting in there but it won't seal up, even with teflon tape. Its giving me fits :banghead: :banghead: :) so any inf will be greatly appreciated. Thanks, Ron.
 
It's a US - NPT (National Pipe Thread) and I think it's 3/8 or 1/2 inch if your using a metric pipe thread then that's why doesn't fit. Good luck :nod:
 
Thanks for the reply Bubba. The one I'm using is a 3/8 NPT and I dont get it. :unsure: I tried some thread grease from ACE and that didnt work, didnt think it would. The aluminum threads cut the heck out of the pipe tape and you can't find adapters/fittings anywhere anymore.

Ron
 
Every so often you will find a fitting that fits a bit loose because they cut the threads a little too deep you could try another one. You can also use some of the Permatex gasket sealer in hardening type if its real loose or the non hardening type if it's at least snug, or some of the Teflon pipe dope that is used for water and gas pipe. Good luck :nod:
 
Will do. I forsee a long weekend ahead. The thing snugs up just fine just wont seal. Its actually made up of three fittings so I'll try a plug first then add pieces in as I go, maybe the brass cracked on the main piece. MTF

Ron
 
Bubba you were spot on. I went stopped on the way home and picked up a new fitting and voila, tight as a drum!

Still wont idle though, it's going to be a long weekend :(
 
:beer: congrats on getting the fitting in a little better. Are you chasing more vacuum leaks? :nod:
 
If you still have good hearing you can use some small rubber Vacuume hose 1/4 to 3/8 inch and listen at the different places along the carb base and intake manifold. And you can also use smoke (about the cleanest way), spray carb cleaner, and a half dozen other ways too to find those Vacuume leaks. Best of luck :nod:
 
Hi Ronbo, How is your project going did you get it running good yet?
 
Bubba, sorry I didnt hit you back with a follow up. Yes the threads on the fitting I had were cheesed so I bought one from Lowes and voila! Tighenet right up. As you know its still not running "right". I'll be chasing a vacuum leak tonight.

Ron
 
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