1970 Intake manifold question

[Jeff Rosansky CLC #28373]

Good morning all.
1970 Deville 472.
I am at my wit's end on this intake manifold gasket.
Little backstory--has always not idled well since rebuild. The builder got sick at the end and I had to get the engine out of the shop quickly at the end. It has never idled well. Had the carb rebuilt at the same time. After sorting out other issues with the engine and then getting sidetracked with the 55 I am now back to the 70. I have always looked for a manifold leak by spraying carb/brake cleaner at the seams.  Never noticed an idle increase until I tried it at about 1000 rpm. Noticed a leak and pulled the manifold. When I pulled it the 1st time I was able to just bump it with my palm and she broke loose (little to no sealer). I redid the gasket but boogered up the corners so I redid it. Before I redid it I put some external sealant on the corner and it sealed OK there. I found the corner leak by blowing smoke in the manifold to narrow down the area but then pinpointed it by blowing lightly in the manifold and spraying soapy water while looking for bubbles. Once the corner was sealed it still didn't idle all that well. So I pulled the manifold again  (quite a chore this time because I used sealant) and redid it. It died on my 1st run after the 2nd gasket and I noticed gas coming out the top of the carb. Found a sunken float that I replaced. Still idles poorly. Can't find any leaks this time with the soapy water trick but when I spray carb cleaner the idle increases. Mostly noticeable around the exhaust crossover ports. So I have to do it again but as you can imagine my fun factor is pretty darn low.
I am wondering if everything is off because they may not have resurfaced the manifold at rebuild. I have no way of knowing how much they took off the heads and block. How can I check this? Is there a thicker aftermarket gasket that I could use this time? I am going to try to get a mechanic friend to look at it to confirm the manifold leak theory but I am very open to suggestions at this point because I want to do this for the last time now.  I got advice here and from MTS on the gasket but it is still an issue.
Thanks for any advice.
Jeff

["Cadillac Kid" Greg Surfas 15364]

Jeff
What gasket are you using?
Greg Surfas

[Dan LeBlanc]

At this point, I would take the intake and have it magnafluxed.  Perhaps there's a crack somewhere.

[Jeff Rosansky CLC #28373]

Just using the turkey pan gasket.
Yes, a crack is a possibility.
Jeff

["Cadillac Kid" Greg Surfas 15364]

Jeff
If you don’t find a crack and you are not leaking from either the vacuum fitting towards the rear OR around the AC compressor bracket bolts that go through to the intake port I would suggest going to the fiber gaskets MTS has for the ports and Permatex “Ultra Black” along the China rails. Greg Surfas

[Jeff Rosansky CLC #28373]

You know, shame on me for not checking. I didn't put anything on the ac compressor bolts. I will put a little dab on those and see what happens. The coil bracket bolts dont go all the way thru tho, do they? I just have thread tape on the rear vac fitting. I will put a little dab on there as well.
Thanks!!

[klinebau]

I am not convinced that you have an intake manifold leak.  Closing the choke slightly will tell you if your carb is running lean as the idle will smooth out.  This may mean that you are simply too lean and just need to add idle fuel.  It does not necessarily mean that there is a vacuum leak.  Spraying carb cleaner is a good way to check for leaks, but you also have to be careful as it can find its way into the carb venturies and trick you into thinking that you have a leak. 

One think you can do to determine if there is a vacuum leak in the intake manifold is to plug the valve cover openings (duct tape) and remove the oil dipstick.  You can put a vac gauge on the dipstick tube to measure the vacuum being pulled on the crankcase.  This is a pretty easy test.

If the intake manifold is off, you can clean everything up and lay the intake manifold on dry  without any gasskets.  You can then use a feeler gauge to see if there are any gaps.  This won't tell you for sure, but will give you an idea if the heads were cut without cutting the manifold.

[Jeff Rosansky CLC #28373]

This is why I love this forum.....
I thought about the spray getting into the carb so I put the air cleaner on it to try and limit what gets sucked in. Acted the same.  I still had some soapy water so I put some on the manifold seam(where I noticed a change when I sprayed) but got no change with just water. I know water is thicker than air/mist but I thought if it was suckling air it may also suck a bit of water but nothing. I just poured a little on, not sprayed.
Good idea on the dipstick tube. Hadn't thought of that. I should get no vacuum reading from the tube, correct?
I also removed the pcv valve. The hose about sucked my finger in. I stuck a bolt in it and there was not much change if any which surprised me.
It runs strong when off idle. Better now than before. If I hadn't gotten the idle change with the spray I was actually thinking of swapping the coil from the 55 onto it to see if I had a bad coil. Plugs and wires brand new. Petronix with a standard coil.
Jeff

[Cape Cod Fleetwood]

Jeff is Big Red running on points or Petronix?

\m/
Laurie?

[Scot Minesinger]

Another quick check to see if you suffer a vacuum leak is to as stated before on other topics, with air cleaner top off and engine idling, run you hand over the intake of the carb to block air (this will make mixture more rich, vacuum leaks make it more lean) and if the idle smooths out this could confirm a leak.  Also, I guess you could just block of the snorkle inlet with your hand and see if idle smooths out. 

Another source of rough idle could be that you are drawing in air from heat riser.  Look down your snorkle inlet with flash light and make sure damper is open to take air in (see edge of blade) not across exhaust manifold.  The switch in air filter housing often fails open to let vacuum to the snorkle damper and then you have this problem.  I always disable this snorkle damper, so it gets no vacuum.

I would make sure your ignition is 100%, good coil, good points, good condenser.

On your carb there idle adjustment screws, and getting those right using a vacuum gauge and following factory procedure smooths out idle too. 

I have done all these things on both my 472 engines; rebuilt 1970 DVC and not rebuilt 39k miles 1970 SDV

[Jeff Rosansky CLC #28373]

Jeff is Big Red running on points or Petronix?
\m/
Laurie?

Red is running a Peteonix. I worked on it some more. Put sealant on the compressor mount bolts too. I get no vacuum from the dipstick tube with the valve covers taped shut. In fact I get about half a pound of pressure which I expect. It does run better when I close the choke slightly so I know I am lean which I will adjust. I am about 2 full turns out on both mixture screws now which is where I put it after I replaced the float. Didn't have time to adjust it this morning after the drive because I took the 55 to a show. Once I adjust the mixture screws, I will swap out the coil from the 55 to be sure that isnt an issue.  Plugs and wires all new.  I know I have done at least some good--- off idle it runs better than ever.  I was always pleased with the power it had before but now she really runs. Left about 4' of rubber at the stoplight. Would have done more but I backed off. Just curious. Guess there us a little teenager under all this gray after all.
Jeff

[Cape Cod Fleetwood]

Red is running a Peteonix. I worked on it some more. Put sealant on the compressor mount bolts too. I get no vacuum from the dipstick tube with the valve covers taped shut. In fact I get about half a pound of pressure which I expect. It does run better when I close the choke slightly so I know I am lean which I will adjust. I am about 2 full turns out on both mixture screws now which is where I put it after I replaced the float. Didn't have time to adjust it this morning after the drive because I took the 55 to a show. Once I adjust the mixture screws, I will swap out the coil from the 55 to be sure that isnt an issue.  Plugs and wires all new.  I know I have done at least some good--- off idle it runs better than ever.  I was always pleased with the power it had before but now she really runs. Left about 4' of rubber at the stoplight. Would have done more but I backed off. Just curious. Guess there us a little teenager under all this gray after all.
Jeff

LOL! Michael is always squealing my wheels when he drives The Ark. I'm like "do you know what those tires COST?" And he's like "stop driving the car like its in a funeral! Beat on it!"

Jeff, just for the halibut (Cape Cod phrase), throw the points back on, see if there's a difference... what do I know. I know when Gary ripped out the EI in The Ark and put points back in, it was a new car. Smoother running, more powerful, etc. YMMV. Good luck with Red.

\m/
Laurie

["Cadillac Kid" Greg Surfas 15364]

Wow,
It sure looks like Laurie has been paying attention.
She's right Jeff. A faulty or improperly adjusted Pertronix set up will run crappy.  Put the points back in (dont forget the ground wire) and see IF that makes a difference.
Greg Surfas

[Jeff Rosansky CLC #28373]

I actually thought about that and was going to swap out the coil and throw points back in until I noticed it does improve when I close the choke slightly. I will tweak the mixture screws a bit until she runs best with the choke fully open. Then will try the coil (easy) and then the points ( not hard but my timing light died so need to borrow one.
It will be next weekend before I can get to it so will keep you updated.

[Cape Cod Fleetwood]

Wow,
It sure looks like Laurie has been paying attention.

<sigh>

\m/
Laurie

[klinebau]

I am about 2 full turns out on both mixture screws now which is where I put it after I replaced the float. 

The factory service manual says that you should be 3 to 6 turns out.  The taper on the mixture screws on the 70 is very gradual compared to other makes and model years.  I have found that mine likes closer to 7 turns out.