Street engines have not only gotten bigger, they’ve also gained compression. Hard starting is an annoying problem that can be resolved either inside or outside the engine. The explanation and tips from S&S Cycle.
The first step in making these beasts more manageable is to check cranking compression with a good screw-in gauge. S&S recommends 180-190 psi for street use, 200 psi for those who insist on pushing the limits. The easiest way to reduce cranking compression is to install a camshaft that closes the intake valve a little later. An engine with the recommended cranking pressure will deliver good power and throttle response but still be reasonably easy to start. Some engines, however, remain stubborn even with moderate cranking pressures. That’s almost always caused by something outside the engine, a worn or binding starter or starter drive, a weak battery ,cheap or old cables, poor wiring connections, inappropriate ignition timing or overly aggressive advance curve, hydraulic lifter bleed-down, or an improperly spaced alternator rotor scraping on the crankcase, just to name a few of the culprits. Whatever the cause, there are several tricks for making a stubborn engine easier to start.
A simple wiring change to remove the lights from the starter-ignition circuit will deliver more current to the starter. The draw back, of course, is that the rider must remember to switch the lights on. It is also possible to wire the ignition and starter circuits separately and use the handlebar “Stop-Run” switch to deactivate the ignition. With the ignition switch on and the handlebar switch in the “Stop” position, all battery current will go to the starter. That gives it more power to get the engine turning, at which point the handlebar switch can be flipped on to activate the ignition and fire the engine.
Another trick that can be extremely effective is to run a second ground cable from the negative terminal of the battery to one of the starter mounting bolts. This reduces resistance between the battery and starter, again increasing current to where it is needed. One last tip is to leave the throttle closed until the engine fires. Opening the throttle admits more air in to the cylinder and increases cranking compression— the last thing you want. With idle set at 1000 RPM, the engine should start with no throttle. Otherwise, pull the throttle back just far enough to get the engine to fire. Hard starting is a nuisance you shouldn’t have to put up with. If your engine has 180–190 psi of cranking compression but remains hard to start, look outside the engine for the cause. If cranking compression is too high, lower your compression ratio or find a cam that closes the intake valve later.