Tell me about a good exhaust for a 258

[Flex BT]

I think I might have an exhaust problem. After letting off the gas (or pushing in clutch) when the engine is revved, there is a really strong gas / exhaust smell. And I know next to nothing about exhaust but I thought it was supposed to run the best with no obstructions, and it ran really poorly before I had the exhaust system hooked up to the manifold fully. I'm taking it to a muffler shop for inspection this month and I figured I'd get them to tell me what I need but I'm sure you all are more knowledgeable about old *** CJs than they are.

As a little bit of background, I've replaced the fuel system from the filler hose to the carb (minus the metal lines), tried three different carbs, done teamrush, installed the manifold heater, removed, inspected, reinstalled both manifolds and valve cover, new charcoal canister, etc.

 

[Torxhead]

If you still have the oem exaust system, changing it out couldn't hurt. I had to next size up pipe installed with a turbo muffler and a straight thru cat. You could have other issues like a rich air-fuel mixture or a fuel tank vent clog

 

[Flex BT]

You could have other issues like a rich air-fuel mixture or a fuel tank vent clog

Interesting... I don't think it'd be a vent clog but tell me how that might be causing the problem. As a side bar, when hooked to the canister is there a vacuum drawn on the fuel tank vent or is it just open? There is a fuel pressure regulator & gauge installed in front of the weber 38 set to the factory specified 3.5psi.

The exhaust isn't OEM, it might be up to the cat which looks old as hell but the muffler looks not-81 and it has some aftermarket tailpipe with a glass pack or something.

 

[Torxhead]

In the space behind the left rear wheel well, there are 2 rollover check valves, or there should be. These will prevent fuel in the tank from entering the charcoal cannister thru the vent line in case of a rollover, or even going down a steep hill, but will allow fuel tank venting. It is part of the fuel tank vent system, a good repair manual will have a diagram of this. Stopping the vehicle will also force fuel into the vent system. If those valves are removed or malfunctioning, gas will flow thru causing the fuel smell, and the bottom of the charcoal cannister will be wet with fuel. There is a vacumn line to the cannister to hold a valve open while the vehicle is running, it also assists in the venting operation also. If the cat is not required, then maybe it should be removed or replaced with a newer straight thru type. From what I have seen on the net, a Weber should have a regulator.

 

[Flex BT]

The PO removed those pieces. I recently discovered this while replacing the tank and have run the vent lines vertical in that rear quarter and installed a rollover / check valve that should be taking care of those functions (I was unable to find an OEM replacement for the liquid check valve). The only issue is if there is a strong vacuum on the fuel line it may be pulling the ball inside the valve upwards, closing the rollover / check valve and not allowing the tank to vent.

I do have a fuel pressure reg installed at 3.5 per Weber. I've tuned and re-tuned the carb many times, I've used a vacuum gauge. I want to say the mix screws are two turns out but I'm not positive.

 

[Torxhead]

To check and see if the tank vent system is working, remove the fuel fill cap. If you do not hear air rushing in, that would indicate that there is air already in the tank and the vent is working. Without a vent system, a vacumn would create in the tank as the fuel gets pumped out, this would affect the fuel pump operation.

 

[Flex BT]

Cool, I'll give that a shot.

Just to clarify for me with the vacuum canister... Are the fuel tank / float bowl lines pulling vacuum towards the canister during operation, or is the deal that the manifold vacuum only opens the port that allows air to freely flow through the can? Another thought for me is that since there is only one ported vac line on the Weber 38 (which connects to the dizzy) the only three connections on my canister are the manifold connection to the top port, then the two on the side (float bowl and tank vents). Does it need to have that other ported vac line connected to it for it to work properly?

If it's the case that it's pulling a vacuum, wouldn't that be the opposite of what you want to happen if there is a vacuum in the fuel tank from the pump?

Torx, you are the man. You've given me a lot of help explaining the dumb things that most people probably figure out on their own (or just don't have jeeps as messed up as mine). Thanks for always taking the time, it has helped me immensely.

 

[Torxhead]

The charcoal cannister purge signal does have a vacumn connection to open the vent to allow filtered air into the line between the carb and pvc valve. If you remove the purge signal cap(The one that says "Do not remove") You can see how the vacumn valve operates and by now it is probably well rotted out and doesn't work any way and would be open providing a constant vacumn leak. It also provides a vacumn into the charcoal chamber to help pull some of the gas fumes out. The other lines provide only venting to the carb float bowl and fuel tank, there is a replaceable filter on the bottom. I have replaced my charcoal cannister with one that only opens that purge signal valve and does not provide vacumn to the cannister. If the gas tank vent system is operating correctly there will be no vacumn in the tank and if there is a vehicle rollover the check valves will close and not allow any fuel from the tank to leak out. I once laid my CJ over and everything worked not allowing any fuel to spill from the gas tank and carb, we pushed it back over and it fired right up. If you don't have emmisions inspection you would not need this vacumn drain. Here in the original land of emmisions testing it is required to have the oem cannister. I am assuming that you have the same cannister that my' 86 came with.