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I have a very long thread going for all sorts of things but figured this will get visibility as far as this holley is concerned: New holley carb 4175 near impossible to get to nuts that screw on to studs. Now here are two issues: what adapter am I using to connect the brake booster? nothing there. And how the heck am I supposed to put the bracket on when there's no clearance on the nuts as it is. The bracket holley sells doesn't specify the 4175 model.
c3 78
Last edited by michael lamoglia; Apr 16, 2021 at 08:50 PM.
I have a very long thread going for all sorts of things but figured this will get visibility as far as this holley is concerned: New holley carb 4175 near impossible to get to nuts that screw on to studs. Now here are two issues: what adapter am I using to connect the brake booster? nothing there. And how the heck am I supposed to put the bracket on when there's no clearance on the nuts as it is. The bracket holley sells doesn't specify the 4175 model.
c3 78
There should be a bushing on your original carburetor throttle plate. Remove it and screw it into your new Holley throttle plate for your booster hard line
There most likely are GM adapter brackets made for the throttle cable.
Either use longer studs or bolt it down.
The steel bushing looks like this, circled in red
Last edited by bmotojoe; Apr 16, 2021 at 09:55 PM.
Go to Summit. Click on fasteners. Enter "Carb Studs". You can get just about any length you want.
Some people put a carb spacer on the Intake requiring longer studs. Simple.
Brake Booster: Looks like a steel line coming from the booster to the carb base. But you have a threaded fitting? IDK
Worse case scenario just cut the steel line and splice in a rubber hose between the two.
I have that carb on my 68 327 350 hp. Like they said, get 1 longer stud. The nuts are a tight fit. I had to lift the carb just a bit to get the nuts to start the threads, then a small wrench. I had issues with carb flooding on hot days when I first got the car. I tried lots of spacers and heat shields,,,, they didn't to shti. I installed the original fuel return line and solved the problem.
Yep....longer studs that do NOT contact the base of the carb...allow about 1/8" gap between the longer studs and the carb base when the studs are screwed into the manifold. As the other members said...the nuts need to be place over each hole in the carb base before lowering the carb onto the studs to be tightened.
Put the nuts in place over the carb base holes and put a TINY drop of superglue on one flat of each nut to hold it in place on the carb base.
If you install the bracket the two nuts will need to be superglued over the holes in the bracket.
I also had to get a fuel filter long housing for the oem fuel line to fit from quadrajet.com.
I think it was a 7/8 by 5/8 inverted flare.
I had to use a holley 20-95 throttle bracket for trans and accelerator cables.
Last edited by speedreed8; Apr 17, 2021 at 10:53 AM.
No it’s not an easy install. I had to also get a 1/4 “ spacer for the oem air cleaner housing so it wouldn’t hit the vacuum secondary housing.
I had to take one of my wrenches for the mounting nuts and grind it down very thin to get in there to tighten them.
But it runs very well now and starts right up.
I tuned it with an afr gauge. Required a few jet changes. And a new lighter spring for the secondaries.
It will run ok out of the box but was a little on the rich side fuel wise for my engine. I also have the Oem L82 aluminum intake manifold.
Last edited by speedreed8; Apr 17, 2021 at 11:23 AM.
Well just to let you know it took about a month to get all the right parts for the install. But that was last year during the pandemic so I was in no hurry. But it will work. I had to modify the holley throttle bracket for the cables by welding a pin in it so it would fit the base on the 4175. But I have a 2004R trans cable. I can get pics. Of my install if you want.
Last edited by speedreed8; Apr 17, 2021 at 11:37 AM.
Got everything back in with old carb (I don’t have the energy to fight with a new carb with modifying brackets etc. left exhaust off just to try and get it turned over. Kicked up after 2 pumps of the gas. Hissed at the carb and shut off. Pumped it twice more and it came up. Revved it to keep it going and shut off. At this point I’m sure it’s adjusting dizzy, etc. it sounded like a tank due to no exhaust manifold connected lol so I stopped. Connected exhaust manifold back up and tried again and it turned over and shut off. I need to advance it I believe. No more explosions. Have to connect the exhaust pipe to manifold so I can hear myself will try tomorrow to fine tune. Success my brothers. All this pain and agony when it was a timing issue in the first place I hope. Moral of the story, don’t remove your dizzy without know where it went and where it’s pointing.
Once I’m good then I’ll pop the Holley in and fine tune. Will need advice on where the hoses go.
holley carb install
