"in Hg" = inches of Mercury. Back in stone age times the vacuum gauges were actually tube filled with Mercury and the vacuum would pull the Mercury up the column. How far it pulled it up was measured in inches. So this became the standard unit of measure. Some motorcycle gauges used to sync multiple carbs still do this. Great video!
Additional pro tip: if you want to see if and where you headers are leaking at the flange - with the car cold (no reason to do warm or hot) get a shop vac, put it on blow, and stick in left or right tail pipe. Jam some shop rags in the other tail pipe to better pressurize the exhaust (you can use some painters tape to tape the pipe and keep the rags in place because the force of the vac will push them out the pipe) get some dawn dish soap and water, mix it in a spray bottle and spray on the header flange. Wherever the leak is you'll see bubbles and foam from where you sprayed ;) Good luck, let me know if you have any questions
I found the exhaust leak. It was the flange on the driver side and the flange with the gasket was put on wrong so I was getting a lot of drone. Now it flows.
Most people don’t realize that a normally aspirated engine won’t run well with vacuum leaks. Your car does sound better and started straight away. The vacuum gauge is also quite handy for carburetor engines, since can be used for a whole host of engine diagnostics. The skills you learn and develop can keep these cars on the road. Keep it up! 😎
Your vacuum leak is plain as day. It is the huge Edelbrock valve cover vent on the passenger valve cover. When you vent your crank case, you must choose between venting to atmosphere, OR positive crankcase ventilation (pcv).. You can't have both. The air is entering the passenger valve cover, traveling through the crankcase to the driver's side valve cover, through the pcv valve and hose, right into the base of the carb. When you run the pcv system, all other vents must be sealed up. No vented oil fill caps, and no vented valve covers.
my 85 318 put 4 barrel intake and carb headers remaned heads, runs great 90,000 on it, has some popping coming out of tailpipe, left the passenger side valve cover breather on without hooking it up to new air cleaner and its got a breather tube open to atmosphere, ill try putting a non breather to see if thats my popping, thanks
Best vacuum at Carb allows best initial throttle response for emulsify of gasoline. I also set timing some with vacuum so to allow a little more Vac for low end throttle response too. Unless I'm racing I prefer like most, street throttle response generally. Good lesson here for others to consider to always use a vacuum gauge!!
Thanks bud my 78 Nova is doing the exact same thing. Tomorrow I will fiddle with it and try and find the source of my needle bouncing like yours. I also notice very slight misfire.
Different things here: First why do you use ported and manfifold at the same time? Secondly it makes sense to start to check the timing before playing with idle mixture screws I think. If your engine used to run hot it is very likely because you feed your distributor vacuum advanced from the ported vacuum. That creates retarted ignition...
did you use Edelbrock recommended intake gaskets? fel pro gaskets are meant to replace factory iron intake gaskets which will not work correctly with an Aluminum Intake .
To find your your vacuum leak, get a can of starter fluid or brake clean (anything flammable) and spray it around your intake gaskets, break booster, pretty much anywhere the car sucks vacuum. If you spray in a spot and your RPM’s go up you have found your leak Also keep a fire extinguisher handy just to be safe. I’ve never had an issue with a fire but it’s better to be safe. A good way to minimize the fire hazard is start the car wait for the choke to open completely then start spraying so everything is not completely hot
Headers being loose won’t cause a vacuum issue... you can run it without headers or any exhaust at all... vacuum issue is probably an intake issue... or a gasket in the carb flange
I think the break booster is going bad. I put a brand new intake and gasket. I put a brand new carburetor gasket as well. When reading the meter, it was stable when I unhooked the line from the break booster. Its old and I'll change that as well. Thanks for the information.
You ever find the other leak? I put a wide band O2 on my car. You can tune the crap out of it so good- idle, cruise, wot, etc. Makes it a dream to know when to swap rods as seasons change
What about the open vacuum line you removed from the carb before you plugged in the gauge. If that’s connected to manifold, you have to plug the end of the line or else that’s a vacuum leak.
There's no need to plug the unplugged vac line, it's only hooked up to the vac module on the trans. The carb is now hooked to the vac gauge. There's no leak there.
valve cover gaskets and header gaskets can't give you vacuum leak header gaskets would just give you an exhaust leak not a vacuum leak valve cover gaskets would just make you leak a little oil
obviously you have your vacuum advance distributor plugged to one of those vacuum ports in the front of that carburetor but what do you have each of them hooked to and which side do you have your distributor hooked I have that same carburetor and by the way I love the Camaros the 70 and a half split bumper if you get an orange one is my favorite and I also love a silver 80 model Z28 anyways I've got a 90 S10 Blazer with a 350 some headers and that same Edelbrock carburetor you have I actually have a RU-vid channel but I totaled my 86 Nissan 300ZX that you see in the channel all I'm left with is my blazer I put the motor in on the channel but anyways I was just wondering about your vacuum ports I just bought me a vacuum gauge to do what you did I hope it helps me out and also check where you plug the vacuum line to your power brake booster that is a check valve and also check your PCV valve
Sounds like you're Friend took advantage of you on the intake manifold,, the cheeper of gaskets should have sealed off the problem,, the gasket is designed to fill in atleat quarter inch gaps,,, Your break booster's probably not bad,, check out the inlet grommet on the booster,,,it will trick you when it wiggles around while driving it will get loose again,, check out the grommet on the PVC, the oil fill cap,,etc,, Find an honest macanic,, Be careful if you retourk the Head bolts you might really mess up your engine,, you will change the Squinch area of the cylinders and bend the rods,,, You need to let someone honest help you
I'll help you Free of charge,, I Hate to see people being taken advantage of because they don't have the knowledge or experience,, I'm here in N.C. but with the iPhone I can help you,,, With that Comaro you should never have needed an intake unless you totally crashed and destroyed your car,, they're set up for street or strip just the way they are,, most of the time you can have one drag race ready for less than 50.00$,,
Hey bro I got a 350 small block iam trying to install in a 1954 jaguar and iam having trouble I saw you’re video and I live in Santa Ana. Close to Costa Mesa. You think you can hook me up with you’re friend to get my motor going and to see the fees of course
Don’t ever sell that car!!! Is that your daily and are you running a fuel pressure regulator? I just got my motor rebuilt and was wondering if I should even run a pressure fuel regulator since my mechanical fuel pump runs at 6psi from edelbrock factory..
you dist. vac. advance should be hooked up to manifold vac. NOT ported vac...also, considering your vac. leak,it could be the vac. diaphram on dist. is leaking..it happened to me..
