ORIGINAL: cmoulder
Some recent updates on the carb and coupler and header...
The static nipple on the carb plate - with the attached fuel tube run inside the fuse - totally elminated the engine sagging (nearly deadstick!) issues when doing outside maneuvers. No change in engine performance at all with the static line installed.
Re the coupler: My max rpm's went down steadily, to the point that the engine was only capable of making 6800 rpm with the 18x10PN. So yesterday I cut the coupler and found that the coupler tape under heat and pressure was somehow rumpling up and constricting the exhaust by about 40%. I didn't have a camera and forgot to keep a piece of it to photograph, but after changing to a piece of Teflon tube the rpm's went right back up. Unfortunately, the Teflon tube I used was not the correct variety and it burned out after a quarter tank of fuel, but at least I have identified the culprit. Unfortunately (further!) the piece of Teflon I have is 5 feet long, so I now have about 4' 8''that I will have to find other uses for. Probably OK for glow, so if anybody has a glow engine and needs some 7/8'' ID Teflon, let me know and I'll send you some.
The tape is fine heat-wise, so my back-up plan is to use a piece of aluminum tube between the header and pipe and then wrap it with the tape. This will prevent any constriction of the tape and should solve the problem. I still have the 7/8'' aluminum wing tube for the Focus, so I know what I'll be using for that job!
The header bolts are holding up absolutely perfectly with the method I used of drilling the bolt heads and making a big clip from 5/64'' piano.
Good info Bob, thanks.
I didn't realize you used a piece of teflon tubing between header and pipe. The typical variety teflon tube you would get at Mc Master Carr is paste extrusion variety which just won't hold up the the heat generated by either gasoline or YS 4 stroke. It isn't so much the teflon tube as much as it is the type of teflon (PTFE actually). There are about 40 different types of raw materials that can be used and of course, McMaster Carr carries the least expensive material since they can make the most money on it. Truth is that for 99.9% of the applications, the stuff is fine.
I kinda wished I knew so I could have steered you clear. Your new approach with the aluminum spacer will work fine.
BTW, what you described happened to me too in a 4 stroke application. There is a teflon type that would work, Teflon 62, but you would not find it at McMaster Carr. It's material used in aerospace and defense aircraft.
A Polyimide tube would work but it is very pricy, more than Teflon. Ally tubing is the simple, practical solution
Matt