Continued Troubleshoot on Gassy Engine

I've started a few threads trying to troubleshoot this problem on a new 455.
The exhaust is way rich and fuel economy is down. While the car is fun to drive, the smell from the exhaust (like raw gas), is disconcerting at best.
I've tried:
Vacuum tests (12-14 psi off of intake)
Checked for intake leaks
Swapped in 3 different carbs in different combinations
Checked PCV
Checked cam timing (Crower #52241, 4" advanced)
Swapped coil, condenser, points, new wires and plugs
Plugs are not black or sooty
New fuel pump
Thought that maybe rings did not seat, used a little SeaFoam, and a few break-in procedures
Fuel pressure normal, tried regulating it
The oil gets gassy, but will not ignite
I have not checked compression. I will get a gauge (to tell you the truth I'm a little scared of what I'll find out, but the car is otherwise running great)

Geez, I hate to belabor you all with this, but I know others might have had this problem or are struggling with it now.
-Gabe

 

A couple q's... are you running a stock intake? What are the specs on the cam...is it a radical one? That vac reading is pretty low for idle. A stock or close cam should have 20-21 inches vac at idle. Compression readings sure will help!

many years ago I ran across a 455 with a similar(sort of) situation. I eventually found that the intake manifold had burned through? the bottom just below the secondaries. Poked it with a screwdriver and it went right through to lifter galley:shock: Musta been a bad casting.?o No:

 

A hole in the intake?! It maybe a weird problem like that! I feel it's either something really simple or something really weird. Knowing me, it's probably the latter.
First, I should add that the gassiness is 'onion cutting' bad. It literally burns my eyes while driving.
The intake is a new Edelbrock Performer.
The cam is 230/236 duration @.050, 112" lobe separation, .504/.505 advertised lift.
I'll get a compression tester soon. I'm just afraid to find out that the engine has to come back out.
If the carb were dumping too much fuel down into it, then I would think the plugs would be sooty, and changing carbs would change the condition?
If the exhaust valves were not seating, then why would the oil get gassy?
If I had bad compression, wouldn't the engine run badly?
Thanks, Gabe.

 

I'm no expert on the 455 so I may be way off the beam with this.

Is it possible that you have the breather pipes connected wrong and that this is drawing fuel/air into the crankcase?

Allan

 

"Gassy Engine"

tum t-um tum Tums.....

Gas in the oil is bad, don't drive it till ya find how its getting there.

 

Thanks, Allan. I'm not sure if I understand the question, but I think everything is right. After all, my engine only has a breather on the driver's side valve cover. All the vacuum ports on the carb are plugged except the PCV and the vacuum advance. The intake has the PCV, trans vacuum and power brakes.
The oil does smell of gas, but I'm not sure if gas actually is entering the crankcase or if the contamination is a byproduct of strong exhaust.
Could the problem be caused by low manifold vacuum not atomizing the fuel properly? What could cause low vacuum? Is there a way to promote fuel atomization? A screen under the carb maybe?
Thanks alot, Gabe

 

What does your timing curve look like?

 

Thanks for the interest.
The carb on there now is a Q-Jet. .075 jets, rods taper from .026 to .050. It's been rebuilt, no leaks, no choke. I've checked that the rods are being pulled down at idle. I've tried another Q-Jet and a Thermoquad from an RV.
I am really interested in this idea of atomization of fuel.
My timing curve is 33" advance all in at 2000 rpm. Thats about 14" initial advance. I would like to try raising the total to 36" again, the fan was chirping and throwing me off (I thought it might be valve ping). You ever get your timing light sucked into the fan? What a thrill!
Thanks again, Gabe

 

Thanks, Larry. I posted my cam specs above. What idle vacuum should I expect for that cam? I have checked the power piston and it is sucked down hard at idle. The vacuum needle vibrates slightly, which may mean all of the plugs are not working optimally. The idle ramps and falls 10 or 20 rpm.
The other thing, I don't know if this is relevant, but the exhaust smells normal for the first 30 seconds after a warm start-up. After that, slowly it starts to fog.
-Gabe

 

Larry, it is definitely exhaust that is gassy, but I'll check again for fuel leaks.
After all of the work and improvements, it seems to have gotten worse. The mpg is down from 12, and the rich exhaust is sharper - more like raw fuel, whereas before it smelled simply of rich exhaust. It burns my nostrils and I'm getting 5-10 mpg.
When I threw on another carb, it would not idle even when the idle screw was cranked all the way in. I had to jam a screw driving in there. That says to me that engine is burning extremely inefficiently.
I've got another carb coming, and I'll try new plugs and wires. Other than that, I'm about to give up.
-Gabe

 

Nice one, Wiz.

Yeah, I believe the Q-Jet is a 2-corner idle carb, meaning the idle will only be drawing off the primaries.

Look at the throttle blades (take the carb off if you have to). Back off the idle screw until the blades close all the way, then turn it in until they are just open a hair. Then start the engine. It should idle - you may have to turn the idle screw in but only a hair more. If it won't idle, then you have a problem other than the carb. Look at the ignition timing. Is the balancer mark correct? Is it an old balancer? Could the outter ring have spun so the timing is way off?

With the throttle blades open a hair, set the timing so it will idle and then check it. Then drive it. Let us know.

 

If you close the throttle plates and cannot get it to idle with them just cracked open and adjusting the idle screw, you can also drill one very small hole about .050" in each of the primary throttle plates on the same side of the bore as the idle slot. You can GRADUALLY increase hole size until you reach the idle quality you desire. But don't start too big!

 

"Continued Troubleshoot on Gassy Engine"


Engine Beno or Gas-X will usually take care of this.

 

You read my mind, Wiz.