[Colorado Uli]

I know of a gentleman who rode his motorcycle over passes in the Andes mountains at extreme altitude (around 15,500 feet).  Predictably, the engine in his bike was running lean because of the low oxygen concentration at this altitude.  He states that he adjusted his carburetors as much as possible to correct for the lean condition, but that this was just not enough.  It should be stated that he is an experienced mechanic.

Seven local residents, including two trackers, and one motorcycle mechanic told him to put garlic in his tank and that this will help with the engine’s performance.  After ignoring their advice for some time because it sounded quite ridiculous, he finally decided that because he wasn’t getting anywhere fast he would throw caution to the wind and give it a try.  According to him, the results of placing two heads of peeled garlic into the fuel tank, suspended by safety wire for easy retrieval, were astonishingly positive providing a very noticeable boost in power.

He also stated to me that “… all the truckers on diesel use onion , all the trucks and 4x4 in the area use garlic on top of the airbox.”  So, there also seems to be a believe that onions work for diesel fuel and that garlic  near the air intake may make a difference as well – but let’s focus on the garlic in gas for now.

Other than to dismiss his observations as simple correlation of other factors not possibly leading to causation because they sound more like folklore, I would like to get to the bottom of this claim.  Could there be a rational explanation for this?  I’ve searched around English language websites for any reference to this claim but have come up empty.
Here is a link to the gentleman’s original posting of this question on a motorcycle riding forum: http://www.advrider.com/forums/showthread.php?t=619276

[billnotgatez]

you could do a controlled experiment

[Colorado Uli]

you could do a controlled experiment

I'd love nothing better than that.  South America, here I come.    
Well, I suppose I could set it up at our slightly lower passes here in Colorado and see if I can find any evidence to support his claim.

However, somebody out there has to have some idea about whether this is possible at all, and why.

[vmelkon]

Why would you drop a garlic in your tank (even if you are using a net) when you can fill a drum with your gasoline and put some garlics in it?

Whether it works or not, I would not do it since it would contribute humidity to the gasoline.

[billnotgatez]

raising the dead I see
tis OK wid me

[Enthalpy]

Very surprising is the tiny proportion of garlic or onion as compared with a fuel tank. It doesn't help to explain any possible effect.

Did you try if garlic contains some burning substance, for instance? Orange peels do.

Altitude not only reduces the pressure and mass of air in the cylinder, it makes it also colder, a serious difficulty for Diesel engines, since compression may not achieve a temperature that ignites the fuel immediately.

In Winter, refineries provide fuel with a lower ignition temperature. I could imagine that a bit of added liquid, easy to vaporize and to light (this is little compatible) would help Diesel engines to light their fuel, but a garlic in a tank, that's really little...

The manual for my old Diesel car states it can run on pure kerosene, especially at cold - legal where the car was bought, but a serious source of worries in other countries. It also suggests to mix up to 15% gasoline to the Diesel oil in intense Winter (for lower viscosity). I'd rather go such ways before trying garlic.