Originally Posted by BikeSmith
Thanks Don. I will try the 1/8th npt. the petcock I have looks like a fine thread pitch of some kind. Crassius. I will try and file the edges. the cap hardly even go's in the hole. and one of the two "teeth" on the cap gets hung up when you try to pull it out. if that will not work. I may just have the machine shop weld in a new thread-in style from an aluminum motorcycle tank or oil overflow tank. that way I have some cool options later on. I need to build a new engine mount anyway. because I am putting a 4stroke kit in the 2 stroke frame. and the mount is too short.
1/8" NPT is a rather fine thread.
The petcock that came with the engine kit 1.5 liter gas tank works just fine in the GT2A frame gas tank fuel outlet boss... not that the Chinese petcocks are all that great, but so far they have worked ok. As to their service life, well that may be an entirely different matter. If you can find a better quality petcock with 1/8" NPT thread you might want to go for it. Or, alternatively drill and tap the GT2 frame tank for a small motorcycle type petcock.
I bought a couple of brass petcocks with 1/8" NPT thread size from gasbike.net that seem to be of a bit better quality (but still not all that robust), but I do consider them a better alternative to the pot metal petcock that is standard in the typical bike engine kit. Unfortunately I fear that just about any petcock you elect to use is going to be a Chinese sourced item... not that that is all bad. I know for a fact from first hand/hands on experience that China can make some really good top notch stuff, and I have several higher end Chinese telescopes sporting superb optics, along with my iPad, iPhone, and MacBook Air that prove it.