This article was published in Pit Stop magazine:

125cc & 250cc MICRO EXHAUST MOUNTING by Jon Fitzpatrick

This article is written for two-stroke car owners & crew, but some of this can be applied to four-stroke exhausts as well.
It may not seem like a big deal to you, but in 14 years of building micro exhausts we have learned that properly mounting the exhaust pipe is very critical. A poorly mounted pipe can crack prematurely and not make the power it should. It can even cause the piston to burn. Most of the micro pipes on the market today are well built and use top quality materials. We learned years ago that thinner pipes make better power and we use 20 gauge cold rolled steel. This makes for a very light pipe, but it has to be mounted to lessen the effects of vibration. It is ultimately up to the car owner or crew to see that the pipe is mounted correctly. Here is how we recommend you go about it.
Two saddle type mounts should be used, one at the rear another up front. We prefer to use a couple of long "screen door" springs wrapped around the saddle instead of hose clamps as they allow some movement and may stretch and save the pipe if a tire gets into it. It also a good idea to "cushion" the saddle. Woven fiberglass repair cloth wired on works well. . If you mount the pipe off of the nerf bar, it is best to bolt nerf solid to chassis. Do not overbuild these mounts. 1/8" steel strap or flat bar will hold the pipe up and can bend away easily in a crash. I've seen fancy machined aluminum or welded tube brackets that guys have obviously spent much time on. I didn't have the heart to tell the them that they would have been better off just using a piece of flat bar that could have made in 5 minutes!
Be sure to adjust your mounts to suit the pipe so that it fits square in the cylinder. Make sure any pivot joints are aligned and not "cocked". Fit the springs so that they pull the pipe up to the cylinder tight. Use at least 2 strong springs to attach it to the cylinder. Some motors may need 4 springs to keep the pipe from pulling away. In the dyno room, we have seen pipes that appear tight, actually blow away from the cylinder under full load. Sometimes as much 1/8"!
Many people are surprised to find out that an air leak in the header area can cause a piston to overheat, seize or cause detonation and preignition. I call this phenomenon "afterburn". The header of a racing two stroke exhaust is mostly filled with fresh fuel / air mixture during the time just before the exhaust port closes. This mixture is "popped" back in the cylinder by the sonic wave returning from the rear cone of the pipe - just as the piston closes the port. This causes a supercharge effect and big power gain. A air leak in this area can cause this mixture to burn in the hot header. You can imagine what happens when this burning mixture gets "popped" back in the cylinder. You have to feel sorry for the piston because it will soon overheat and fail. Over richening the jetting will only "add fuel to the fire." As usual the "Evil two-stroke" is blamed but the fault sometimes goes to the guy "looking back in the mirror."
WELDING: With the variety of chassis designs and engine combinations it is impossible to produce a pipe that will fit every car exactly. You may need to cut and twist some pipes to fit the car better. If you have to weld on the pipe, gas welding with a small tip is best. T.I.G. welding can be used on the pipe, but, we recommend you stress relieve T.I.G. welds with a gas torch by heating to a dull red and allow it to cool slowly. Do not mig weld on a pipe or try to braze over a crack as it will most likely crack again. Brazing is recommended for putting on any mounting brackets or spring eyelets. Never alter the length of the pipe as sent- We spend many hours on the dyno working out the best length for power output.
You should have some spare pipe springs and O-rings with you at the track.
Remember; Do your homework and get that pipe on right!
Good Luck, Jon

" Jon Fitzpatrick most of you know is the owner of FTZ Performance of Cape Girardeau, Missouri."