Adding a tuned pipe to your engine can give a significant performance boost. There are quite tuned pipes that give less performance than standard tuned pipes but make less sound. Tuned pipes work by forcing raw unburned fuel that has escaped through the exhaust port back into the combustion chamber just before the piston closes the port. This extra charge of fuel can give 500 to 1000+ more rpm over stock mufflers. If you are using a tuned pipe that is ready to attach there should be no problem just bolt it on and go. However most tuned pipes come in two parts, the header that attaches to the engine and the tuned pipe its self.
Check RPMs before you add the tuned pipe. (remember it)
First if your tuned pipe does not have a pressure fitting installed like the Macs 1140 (Check out their web site) you must install one. The walls of the pipe are not thick enough to support a threaded pressure fitting alone. Your best bet is to get a pressure fitting that has a nut that fits on the inside of the pipe. You want to install the pressure fitting just before the largest part of the pipe (typically a little ways before the middle). Drill and tap some threads at this location and screw in the fitting. Run some dental floss through the pressure fitting and out the exhaust and slide the nut down the floss and onto the pressure fitting. Use something like extended tweezers to tighten the nut down, I fear this part may entitle you to some creative thinking.
Now its time to set up the exhaust header. Most times when the exhaust header comes it is too long especially the Macs headers but don't just chop it in half right away. This is the part where your tune in your pipe by cutting off 1/2 inch sections at a time. First attach the header (make sure you use a gasket between it and the engine) attach the pipe to the header with heat resistant silicone rubber exhaust coupler and leave about ½ inch between the tuned pipe and the header. Start the engine and make sure it is running like it should (slight needle adjustment may be required) take an RPM reading and then shut down the engine. (Should be higher than the first reading in step 1) Cut ½ inch off the Header and check RPMs. If the RPMs when up cut another ¼ to ½ inch off until there is no increase in RPMs (but never more than half the header should be removed) that should do it. If the RPMs did not go up when you made your first cut, remove a ¼ inch more and if still no increase you have already obtained optimum distance.
If your new tuned pipe causes you to burn glow plugs you may need to switch to a cooler glow plug and if that still doesn't help try using less nitro.