On the fitting toward the intake or carburetor I've added a 1/16th" hole flow restrictor. This is snug fitting bolt screwed into the fitting then sawed off. The 1/16th" hole drilled will allow sufficient flow of HHO under normal conditions but help prevent flames from a back fire from passing. This is a 3rd measure of protection that can be added to this assembly. If this is not going to be added to a vacuum line and there is a high volume of HHO being generated, this hole can cause pressure to develop behind inside the flashback preventer itself. No problem as hydrogen does not become more explosive under pressure like many other gases, but the pressure can find leaks in hoses if you are not careful. If HHO volume is creating excessive pressure and you worry about hoses blowing off then increase the size of the hole in this flow restrictor to around 3/32" for safety.

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