Strange RPM intake port leak?
 

What is the typical cause of a RPM intake not sealing off on a '69 head?

Had something super strange happen today. I went to do the cam break-in on that 69 400 I did a cam swap on. So I roll the car outside and fill the 750 double pumper with gas. Somehow when I put gas into the secondary bowl vent, all the gas came out the boosters and filled the intake with about 4oz of gas. That's most of what I put in, so it all went right down the intake. A subject for another thread I guess.

But the weird thing is that gas started to show up on the valley pan and run down the front of the engine block. WTF? Close investigation found the intake runner for cyls 2&4 were not sealed to the head, at the bottom of the port. So the gas runs down the runner and leaked out of the bottom of the port. Needless to say I didn't try to fire it off.

I pulled the intake off and didn't find anything super obvious, other than the impression from the intake on the gasket was faint, basically sucked. Bolts were tight, the intake wasn't hitting the valley pan, the gaskets are the fel-pro 9980. The intake came with the motor and there was skin coat of sealer on both sides of the gaskets that came out. The valley pan is new from Butler and I clearanced it for the intake.

The orange alignment plugs were in place, but were mashed to chit. Can they hold the intake off that badly? Is the RPM supposed to have a relief machined for them? What likely happened?

Looks like wrong gaskets,need the smaller heat X over hole.Just did a engine with a set of 48s.Tom

Bottom of intake (at ports) hitting the valley pan preventing a proper seal when torqued down?

Decking a block and/or milling heads can cause issues with the intake fitting over the valley pan. Some grinding on the valley pan may be needed.

For what it’s worth I never leave those orange guides in the gasket, I don’t feel like they squash down all the way, not saying it will have a problem every single time but the only reason I use those for scribing my lines for port matching, but sounds like the heads might not have been milled perfectly slat leaving a slight Lee bigger gap at the bottom of your intake gasket than the top, or manufacturer error

Some people will grind a beveled edge along both bottom sides off intake for valley clearance. I had the same issue as you, but i trimmed down the cork gasket on the pan as far as i could, without any grinding for clearance. But beveling intake would work better.

X2 with post 3.

Pull the valley pan off and only seal it with gray form-a- gasket.
Do not use a gasket!
I , as others have found that they never fit 100% right anyway!

Then get some some clay or aluminum foil, ball some up and sit it on the left and right side of the lip of the valley pan.

Next drop the intake on with no gasket and see if it still rest on the lip of the valley pan.

If it does then you know you you’ve got some trim grinding to do as posted above also.

Ideally you want a hair of clearance without the intake gasket in place unless you are using a thick Mr Gasket .050” type already.

he said the intake wasnt hitting the valley pan... but worth double checking that again.

i use the tomahawk v/p that is the same as what butler is selling and it needed to be clearanced a little more in the areas where the intake ports are on a factory 69 iron intake, i did a little grinding on those areas of the intake too just to be sure.

Those plastic gasket holders aren’t design to be squished with the gasket. The factory intakes are cut back to clear them. I usually use a little silicone on both sides of the gasket around the water crossover and a little on the other end to hold the gaskets in place. HTH

I'd look at this. Looks like the bottom of the runners are as cast. Most need some grinding at the bottom.

Another possibility
 

I notice in your pic that the PCV line appears to have been run back under the intake on top of the valley pan.

I also notice that the hose is routed over almost the highest spot on the valley pan - right next to the intake ports for cylinders #2 and #4.

I don't recall how much clearance there is between the bottom of the intake and the valley pan, but it's probably not too much.

Is there a possibility that the hose it somehow taller than the clearance at that point and that it is holding the intake up just slightly?

So that's something else for you to check. Good luck!

+1
Some manufacturing lots of the RPM needed the head surfaces milled right out of the box to fit.
The silicone on the gaskets when it was removed might have been a clue.

All good suggestions!
I went back and clearanced the chit out of the intake runners with a die grinder. I layed them back further after i took the below pictures and test fit it. They now clear the valley pan with no gasket. I added countersinks in the intake flange for the orange gasket locators. I also chased all the intake threads with a tap.

Responses to a few observations:
Intake bolt holes line up with no gasket installed.
I routed the PCV hose after I had the intake installed, so it shouldn't have affected things.
The valley pan was clearanced before I installed it without a gasket. .
The PO did make a reference to intake leaks with this RPM intake but I shrugged it off. This is the same motor that supposedly had years of carb problems with a tri-power setup.
No idea of engine history, can't tell if it was decked. Intake flanges on heads are stock. Looks like a basic ring and bearing job 30 years ago.

What else do I need to check before I try to put it back together?
How can I tell if the intake flanges are at the wrong angle?

when i tried to put an new RPM intake on a 400 with 62's, it really wouldn't fit. with the felpro gaskets in place, the bolt holes didn't line up for nothing. take out the gaskets and they were centered in the intake holes. measured the gaskets to be .060 thick and had that milled off the each side of the intake flanges. the holes were now centered with the gasket in place. ended up having to clearance the valley pan as well.

I had another RPM that had been cut .060 for an engine that had been decked. I test fit it on this engine with a gasket and it didn't fit, there were gaps at the ports. I pulled it off and put the uncut RPM back on. This time it looks like the intake cinched down properly on the gaskets.

It's now all back together waiting on me to fire it off. By the way, do you need to prime the secondary fuel bowl on a QF 750 doublepumper? Will it run well on the primary bowl long enough for the pump to refill the carb?

Priming the font bowl only will work.
 

You only need the gas in the front to start the engine.

The secondary bowl will fill as soon as the engine starts.

Good luck!

That carb is a 4 corner idle circuit type.

While yes, it will start with just the primary fuel bowl filled up it will not idle properly until the secondary is near filled also.