has problems starting most of the time

Dave Scott could be many of things. If it has spark it most likely has spark when it is back in the cylinder head. So that would leave either fuel or air as a possibility. Check your fuel filter and pump to make sure that you have the right fuel pressure on that. The other thing you need to check for is that the spark happens a the right time. So you need to check the crank position as well as the cam position sensors. I would strongly suggest that when it runs, take it where they can scan the vehicle 's OBD to see if and what codes you get. Otherwise you might be spending a lot of money for parts that are not needed. Depending on where you are, places like Autozone do the scanning for free. Let us know what the exact engine is and what you have checked so that we may provide a more in depth answer