Bigger jets allow more fuel and smaller jets allow less. The rejetting process figures out which size jets is needed to keep an engine running with the right mixture. Too little fuel and the engine may starve or overheat at high RPMs.Too much fuel and the engine could flood and bog out.hares & Saves. Save. Replacing an exhaust with a carburetor-type engine is more than just bolting on a new pipe. Whether it’s a car or motorcycle or scooter, you are likely going to need to make sure your carburetor is running with the correct jetting for the new exhaust.