MASSIVE Vacuum Leak

[69SatelliteGuy]

Hey all, here again with another engine problem. I know nothing about engines really, but recently swapped my carter 2BBL and intake over to a Holley Street Dominator intake and Holley 4160. Now, I rebuilt the Holley because it was NOS from the '70s and put new intake manifold gaskets, the metal ones. It was fine for a bit, but lately it wont idle in gear. Park, Neutral, just fine. The minute it goes into gear, boom dead. Instantly, can't even keep it running. So I tried adjusting screws and timing and what not, it didn't help. I decided to smother the carb, and the RPM shot up. Okay, so I sprayed the base of the carb and where the intake meets the heads with brake clean, revs up doing that too. Can I seriously have a vacuum leak coming from everything after no issues for a couple days?

 

[Mick56]

You could try to retorque the bolts.

 

[69SatelliteGuy]

Yeah, I think I'll try that tomorrow. Seems crazy that it would be leaking from everywhere.

 

[MoparLeo]

What type/brand of gaskets are you using on the intake( what engine size) and on the carb base ? Pictures would be a great help as you can imagine. We can't see what you see.

 

[69SatelliteGuy]

Intake was a brand new set from Felpro. Didn't use the cork for the front or back, packed it with Black Permatex instead. The carb base gasket is from Edelbrock, needed a spacer so just bought the little kit. Engine is 318, nothing modified that I'm aware of.

 

[Slap Stick]

Something tells me you will need to remove the intake and install the end gaskets using a dab of sealer at the corners.
If the sealer got sucked into the engine that would make a yuuuge vacuum leak.

 

[coronet68mx]

Did you follow the sequence, and torque the bolts according to the intake specs

 

[MoparLeo]

So instead of a gasket at the front and rear of the intake manifold, you only used liquid silicone ? Ant reason to not use a gasket ? Guaranteed to leak with out it and possibly suck silicone into your engine. A 318 has small intake ports. Was this manifold specifically for the 318 . Did you compare the gasket to the head and manifold port sizes before install ?
And another note, the metal gaskets are NOT for aluminum intake manifolds. They will not seal.

 

[Ironbuilt]

As stated above, I would bet your problem is directly related to you eliminating the cork gaskets. Start over, use the correct gaskets and be sure to torque to specs in the correct order.

 

[69SatelliteGuy]

The bolts were torqued to 35 Ft. Lbs. I read that a lot of people don't use the cork for some reason so I followed suit, no other reason. The intake was specifically for Chrysler small blocks. It was NOS too from around 1975. The instructions called for a Chrysler intake manifold gasket kit, I can't imagine they would've had non metal ones at a dealer in '75, right?

 

[eldubb440]

I've eliminated the front and rear cork or rubber seals for decades with never an issue......I always use permatex "rite stuff" in the "cheeze wiz" style can........ a nice fat, tall bead allowing a day or 2 to cure

failure at that point would only lead to the pvc sucking air through that spot into the lifter valley, instead of sucking through the breather cap (unless you have serious blow by, then it would push out, not in) ...... that spot can NOT cause air to be sucked into the intake runners or combustion chambers where it would cause a lean condition and a change in RPM

your leak is most likely where the intake meets the head, or at the base gasket of the carb. (or your pcv hose fell off) a failed brake booster can also ruin your day, but that isn't what you described

matter of fact, I installed an aluminum intake on a 318 a few nights ago for a friend of mine on his jeep, I cheese wizzed it up and expect no issues

 

[oldkimmer]

U need the composite gaskets for an aluminum intake. The intake could of been milled at 1 time and is now too narrow. U may need thicker gaskets. 90% of ppl do not use the cork gaskets on the end rails. Kim

 

[turbine68rt]

Intake was a brand new set from Felpro. Didn't use the cork for the front or back, packed it with Black Permatex instead. The carb base gasket is from Edelbrock, needed a spacer so just bought the little kit. Engine is 318, nothing modified that I'm aware of.

Did you use 340 intake gaskets?

 

[Kern Dog]

So instead of a gasket at the front and rear of the intake manifold, you only used liquid silicone ? Ant reason to not use a gasket ? Guaranteed to leak with out it and possibly suck silicone into your engine.

F A L S E.
It is a common practice to use an RTV sealant in place of a gasket in many instances. I'm not talking just the cheapest blue or black goo but quality oil and gas resistant RTV.
The transmission pan in my 2007 Ram and the differential cover are the newest examples that I can think of.
Chevy small block V8s have a similar intake design and they have been advised to omit the gaskets and use RTV for 20-25 years.

 

[65-440]

I don't run front or rear gaskets either, no problems.... the issue with those ens seals is (for me at least) it causes the intake to sit way high and off the heads. A thick bead of ultra black sealer and let it cure overnight. Do you have a stethoscope? If so let it idle, remove the metal end of the stethoscope leaving just the rubber hose attached to the ear pieces and move that hose end around the intake... you'll hear the leak when you find it.

 

[65-440]

F A L S E.
It is a common practice to use an RTV sealant in place of a gasket in many instances. I'm not talking just the cheapest blue or black goo but quality oil and gas resistant RTV.
The transmission pan in my 2007 Ram and the differential cover are the newest examples that I can think of.
Chevy small block V8s have a similar intake design and they have been advised to omit the gaskets and use RTV for 20-25 years.

Exactly... I'll be removing the trans pan on my 68 and sealing it directly to the case. I cannot get it to stop leaking to save my life. Bone dry above the pan, selector shaft/cooler lines/NSS/dipstick tube all dry....it only leaks after it sits for a few days, if I drive it a few days a week it'll never leak. I blame converter drain back, but still shouldn't leak if the pan was sealed!

 

[PurpleBeeper]

Back to the poster's problem..... unfortunately, the intake is definitely leaking at the ports (front/rear gaskets are un-related to your vacuum leak). Remove intake, replace gasket, torque bolts in steps middle (by carb) to outer & re-check with carb cleaner if you still have a leak.

IF..... IF, it still leaks, you may have another issue, but that's unlikely. I think re-doing the intake gasket will fix it.

 

[ckessel]

A couple of things to check. You need to check the port size of the intake compared to the head port size. Some manufactures would show that the manifold would fit 273-360 but leave out the tidbit that although it bolts on, there is a big difference in the port size between 273/318 and 340/360. This is one potential source of the leak. If thats it, you'l need to get a manifold for the smaller port size. Second issue would be if the heads have been cut enough, you will have a mismatch that will uncover the ports. Your manifold may need to get cut too if the heads have had enough removed from them.

 

[69SatelliteGuy]

The heads look to be original and untouched, much like the car. I have no doubt the 75,000 on it are original. I have the original intake and carb still so if the issues persist that’s going back on. Like I said, the intake was NOS, it had never been put on a car, still was in the Holley box. I have another set of intake gaskets, so if I re torque it tonight and nothing changes the manifold is coming off.

 

[69SatelliteGuy]

Alright, Ive re-torqued and if I spray the base and the manifold with brake clean it doesn't seem to shoot up in RPM anymore, but it still wont idle in gear. Hoped it was my problem, but it seems not so. Probably will go back to my 2 barrel. I'm building a 383 for it anyway...