Expert: Everett Peacock - 2/7/2009

Question
I have a 2000 Mercruiser (4.3L) with Thunderbolt V carbureted ignition (engine s/n 0L565516).  At times, it can be difficult to start, especially when hot. I know it "could" be vapor lock, but I am not convinced yet.  I do have the common-for-these-engines run on problem when shutting off the engine.  I tried colder spark plugs (NGK-TR6), and this did not solve the run on issue.  Could the colder plugs contribute to difficult starts?  The distributor cap, rotor, and plug wires have two seasons on them (about 30 – 40 hours per season).  I did replace the ignition sensor at the same time as changing to colder plugs.  The new ignition sensor is different (improved) design (the old sensor had corroded).  The engine runs perfect once started.  The other odd starting concern is when the engine is cold, it sometimes has to crank for a long period before starting and then when it does begin to start it begins slow and I still need to keep the starter running for a few seconds until it finally gets to normal idle speed.  This season, I plan to replace the distributor and rotor and probably go back to the normal heat range spark plug.  After that, I am running out of ideas.  Could it be a fuel flow problem, but only at starting?  Anything with the timing adjustment?  Other suggestions?  Carburetor is clean and so is the spark arrestor filter.  I understand there may be another plastic filter in the fuel line just before the carburetor (in addition to the fuel-water separator, which is replaced each year)?

Thanks for any suggestions you may have,

Steve


Answer
check all your sensers, oil pressure sensors.. you have a connections  on it that get corroded..low pressure switch is on the right side of the engine if you were in the boat..facing the engine......the sender  on the intake is for the oil pressure gauge on the dash...