So - this weekend, I rode the LS1 miata harder than before with a mountain run, keeping the RPMs higher and the car did great. No overheating.

The problem is - after about an hour of driving, I kept hearing a noise in the rear - turned out to be my gas cap. When we stopped for a break, I released the pressure in the tank (a lot of pressure) and the engine immediately died (vapor lock). Had to wait until it cooled before the engine would crank.

The fuel tank was filled before the drive and when I released the pressure, the fuel was pretty hot.

2-questions:

1. Is there a preferred gas cap for the LS1 swapped NA?
2. I think I need to add heat shield on the fuel tank?

 

Mine used to do the same thing. I disassembled the cap & cleaned the stuff off of the "screen" inside of it. You will understand what I am talking about when you take the cap apart. No special tools needed, just a pocket screwdriver to release the clips. This helped mine some. What really made a huge difference, was blowing out the vapor line. With the gas cap removed, I applied a small amount of compressed air to the vapor line before the purge valve. Apparently there is some sort of check valve that was stuck, not allowing the vapor to purge. I have had zero pressure build-up since, & my garage does not smell like raw gas anymore.

 

The heat may be a bigger issue - the exhaust may be driving the tank temp to the boiling point of the fuel? I will be looking into that for sure... anybody else have this issue?

 

The heat IS an issue, but if the pressure cannot be purged, the heat will continue to rise. My fuel was damn near boiling on a trip to Road Atlanta last year. Car gradually started to run bad. I ended up topping off the tank with some fresh cold gas & leaving the cap off for the ride home with no issues. No problems since above repairs (that were free).

 

I was able to replumb the venting maze to allow for pressure release. If you look at ToySnake's plumbing on his tank (page 9), that is exactly how mine looks. The vent line then runs to a charcoal canister that is mounted under the passenger fender where vapors ultimately vent to atmosphere.

I ended up making my own charcoal canister from a popup sprinkler head (found details on a factory five forum). 4 inch sprinkler head - gutted, added scotch brite to each end and fish tank active carbon (charcoal) which comes in a net bag fits perfectly. screw the top back on and a barb fitting to the other end and connect to the vent line. Viola!

I also wrapped the pipes (header wrap) below and near the fuel tank/filter to reduce the heat in that area. My X-Pipe is pretty close to the filter - its now wrapped.

I tested with the car yesterday and only a slight bit of pressure builds - as expected - but not the way it was previous to the "fix".

 

"I ended up making my own charcoal canister from a popup sprinkler head (found details on a factory five forum). 4 inch sprinkler head - gutted, added scotch brite to each end and fish tank active carbon (charcoal) which comes in a net bag fits perfectly. screw the top back on and a barb fitting to the other end and connect to the vent line. Viola!" -- SB5700

Awesome. So you just plumbed in the new charcoal canister, and you're off to the races and it's all good? I hope so as that would confirm that I'm headed in the right direction.

 

I have not had any problems but am thinking about doing the same thing. I have the canister from the Miata still and a good spot to put it. What do you guys thing about putting a valve in the system to be open when the engine is running and close with it off? My thought is that would eliminate any possibility of having a gas smell in the garage.

 

Confirmed!

 

The canister seems to be doing its job for now (absorbing the smell while allowing the vapor to escape), and mine is completely serviceable (cheap).

In my application, since I don't have a purge port on my canister, it would go between the tank and the canister (in regular applications, I assume it would go downstream from the canister) - to open the vent while the engine is running, and close it off while its not. It would be easy enough to plumb and wire...