Gas vapors for my rider

[ghost civic]

Ive been messing with a 2000ish john deere riding mower that I plan to make into a go kart.
The thing had sat for a year or 2 and the carb was gummed up bad and the filter and some lines had to be replaced.
Even after multiple cleanings of the carb (carb cleaner and boiling it with lemon juice) it still will not run right. It start fine, can rev to about 3/4 throttle but dies at full throttle. It runs fine anywhere from 0 throttle to 75%...but you also have to adjust the throttle slowly...do it fast (going up) and it will die.

Anyway, that what I have to work with. I stumbled on a webpage talking about fuel vaporize systems...which basically allow you to bypass the carb.
The idea seems simple and sound...have air going into your gas tank and then the carb inlet pulls both air and gas vapors directly from the tank. Since the fuel is already "vaporized" and mixed with air, all the carb needs to do is meter the charge going in via the butterfly.

Most of the setups Ive seen used some other container as a fuel tank. But I figure I can use the stock fuel tank and make a air inlet line and a vapor fuel exit line go through the gas cap.

I am a bit skeptical. While I believe that a engine will run on vapors...having the ratio of fuel/air be right might not be so easy. But, since I have a carb that wont work right and would cost over $100 to replace and trying a vapor setup wont cost more than $10 in parts from a hardware store I figure why not try it and see for myself.

Basically, I plan to put to barbed hose fitting through the gas tank cap. One will put a hose down into the tank and have a air filter on the outside. The other will take air/vapor from the tank directly to the carb inlet. This line will have a "T" fitting on it and a ball valve on the other side of the "T". The purpose of that valve will be so I can adjust the fuel/air mixture. If it runs rich, I can open the valve a touch and add air to the mixture being pulled from the tank.

anyone wanna give their thoughts on if/how well it will work?

 

[Badot]

How much the gas evaporates into the air being pulled through would vary with so many different factors that you'd likely have to build something more complicated than a carb to keep the mix decent... unless you want to constantly fiddle with it by hand.

On the safety side of things, there's also the very real chance that a backfire could detonate your entire gas tank, sending burning fuel and shrapnel everywhere in the immediate vicinity... so that would be fun.

 

[ghost civic]

oh yeh, the backfire issue. It was mentioned in some of the stuff I read, but a simple flame arrester isn't hard to make. Metal mesh screen in the line will keep a flame from traveling into the tank.

I did read that on larger engines...where the amount of vapors used would be higher, that a radiator like device is used to help the fuel vaporize faster.

I do also wonder if the amount of vapor given off will change based on the amount of fuel in the tank. The amount of air being drawn into the tank would remain the same and is part of what helps the fuel vaporize, but the amount of fuel in the tank could change the amount of vapor/air ratio.

I hate to say this, I was going to do it for fun...but today I realized that the motor in the john deere is the same as my husky. Which means if I were to blow it up testing this out, I would ruin a motor I could have used if the one on my husky goes.

I will still do a quick and easy test...just run a hose from a jar of fuel (hose above the fuel, not in it) to the carb air intake and disconnect the fuel line and see if it will fire or not. If it does, then the basic concept is true. But I agree that the amount of available vapor in the tank could vary and cause issues.

 

[Badot]

Flame arrestors have a surprising amount of science behind them, some random metal mesh may work, but it may not. I'm pretty sure a gas/air mix at the proper ratio will need a very fine mesh to stop the flame though.

I just don't think it would be practical. At the very least you'd need to change the mix depending on the temperature of the fuel, temperature of the air, flow and turbulence of the air, and fuel surface area in the tank. And all those conditions are constantly changing through normal operation. It might be able to run, but it'll likely never run well, or for long.

If your goal with this is just to play around with it I'm sure you could succeed in getting it to run... but you're replacing a precisely designed and built automatic metering device with technology that was deficient since before 1900 built using random parts from a hardware store.

 

[ezcome-ezgo]

This will not work. Although gasoline is a potent fuel, its vapors at atmospheric pressure and ambient temperature do not have enough energy to do what you are suggesting. The fuel would have to be essentially distilled (heated and and the gasses condensed) for this to work. It would take additional energy from another source to make that happen.

 

[machinist@large]

This will not work. Although gasoline is a potent fuel, its vapors at atmospheric pressure and ambient temperature do not have enough energy to do what you are suggesting. The fuel would have to be essentially distilled (heated and and the gasses condensed) for this to work. It would take additional energy from another source to make that happen.

While you and Badot are both correct in that the thing won't run that way, there's one thing that you missed.

Trying to distill gasoline is a loosing proposition energy wise since its already a distillate of crude oil. Any further effort will just boil off the stuff you want in form's that are much more difficult to deal with.....