Gas vapor out the secondaries at WOT

[Tealliberator]

I have a 350 magnum with a quadrajet in a 1987 Liberator. The boat will run great at idle and up to about 3500 rpm. When the secondaries open, it appears a lot of gas fumes are coming from the secondaries and the engine will only go to 4000 rpm. Top speed used to be 55, but barely get 45 now. I have had the carb rebuilt, put in a new delco ignition, checked the vacuum, but can not get this figured out. Anyone experience this? My next step is to yank the quadrajet and replace with a Holly 625.

 

[kenny nunez]

Does the exhaust exit through the drive or through the transom?
How is the compression. Did this symptom happen all at once or gradually?
I do not think you have a carburetor problem. Something else is causing the problem.

 

[Tealliberator]

Does the exhaust exit through the drive or through the transom?
How is the compression. Did this symptom happen all at once or gradually?
I do not think you have a carburetor problem. Something else is causing the problem.

The exhaust is through the transom.
The compression is all good. The engine has about 120 hrs. I think I had multiple problems starting with the old Thunderbolt IV. It had a firing problem then I changed the module under the distributor. It ran better, but not up to full RPM. I replaced the entire ignition with the Delco set up. It fires right up and runs well until I get into the secondaires. The vacuum at idle is 17 and goes to 25 when I hit the throttle in neutral. I was thinking cam or head gasket, but not sure of anything at the moment.

 

[alldodge]

Carb needs different jets and/or rods need changed. Your running rich

Check out Cliffs high performance

 

[Lou C]

are you sure that both the secondary throttle blades and the secondary air doors above them are opening?

 

[Tealliberator]

are you sure that both the secondary throttle blades and the secondary air doors above them are opening?

I will check that out, but the top doors are definitely open.

 

[Tealliberator]

Does the exhaust exit through the drive or through the transom?
How is the compression. Did this symptom happen all at once or gradually?
I do not think you have a carburetor problem. Something else is causing the problem.

You are correct. Something else is going on. I changed the carb and the boat actually ran worse. It sounds perfect revving in neutral, but under load it is terrible. Barely gets on step then floods when the secondaries start to open. I wonder if I have bent pushrods?

 

[Scott Danforth]

check compression

its not the pushrods, or it would sound like a bucket of marbles in the drier

reving in neutral can be done with only 4 cylinders firing and very little fuel. It means nothing

running terrible under load is usually fuel system (lack of sufficient fuel)

 

[Tealliberator]

check compression

its not the pushrods, or it would sound like a bucket of marbles in the drier

reving in neutral can be done with only 4 cylinders firing and very little fuel. It means nothing

running terrible under load is usually fuel system (lack of sufficient fuel)

Well I just got around to checking the compression, and it is not good. Cylinders 1 - 7 are 50 or less. Cylinders 2 - 8 are 180 to 200. I guess I have a blown head gasket?

 

[Scott Danforth]

or leaking exhaust manifold and rusted valve seats.

BTW, since a new motor is 150 psi, if you have 180-200 psi, you either have water in the cylinders or you have a bad gauge

 

[Tealliberator]

or leaking exhaust manifold and rusted valve seats.

BTW, since a new motor is 150 psi, if you have 180-200 psi, you either have water in the cylinders or you have a bad gauge

 

[Tealliberator]

The gage is about 40 years old, so that could be, The plugs on the stbd side all look good, but the port side did have a little bit of rust around the rim of the plug

 

[Tealliberator]

Is there a good way to narrow down if it is the head gasket, exhaust gasket or valves?

 

[Lou C]

You can do a cyl leak down test before taking anything apart. If the leakage is from the valves you can pull the heads with the engine in the boat but if it’s rings then the motor is coming out.

 

[alldodge]

rust around the rim of the plug

Heads need to come off

 

[Lou C]

Break out your impact gun for the head bolts and those intake manifolds can get really stuck on. I was able to get the head bolts out easily but the baked on old intake gaskets were like kryptonite

 

[Scott Danforth]

Is there a good way to narrow down if it is the head gasket, exhaust gasket or valves?

pull the exhaust manifolds, if its rusty valves, the exhaust ports will look like rusty hell. at that point, you are pulling the head.

 

[Tealliberator]

pull the exhaust manifolds, if its rusty valves, the exhaust ports will look like rusty hell. at that point, you are pulling the head.

I pulled the exhaust and there is no rust. The nuts on top of the rockers are milky though, but the oil is clean. I am not sure condensation would cause the milkyness on just the rocker nuts? I checked the torque on the head bolts and all is good. Re-checked compression and only 25 psi on cylinders 1 -7 but 170 psi on 2 - 8.. I wonder if I should just pull the one head or go ahead and pull both?

 

[Grub54891]

I pulled the exhaust and there is no rust. The nuts on top of the rockers are milky though, but the oil is clean. I am not sure condensation would cause the milkyness on just the rocker nuts? I checked the torque on the head bolts and all is good. Re-checked compression and only 25 psi on cylinders 1 -7 but 170 psi on 2 - 8.. I wonder if I should just pull the one head or go ahead and pull both?

Pull both. Head gasket kits come with both anyway. And you will have the comfort of knowing both sides were done properly.

 

[tank1949]

The gage is about 40 years old, so that could be, The plugs on the stbd side all look good, but the port side did have a little bit of rust around the rim of the plug

I experienced compression tester failures due to a fitting malfunction. Air fitting was leaking badly. Try another compression tester or tighten its fittings. Trust me!!!