'78 Mercruiser 305 Chevy Starting Problems

[Bob K.]

Hi all, I'd be curious to see what everyone thinks about a problem I'm having with my boat. The engines are '78 Mercruiser 305 Chevys which are coupled to outdrives (I think that is the correct name for gear boxes which drive propeller shafts). One of the engines has a hot starting problem, when started cold it works fine although it takes a few cranks to get it going. After taking the boat out, docking it and shutting it off it will not restart while hot. It seems like the engine is flooded and we can't even get a pop out of it. So far we have done the following: checked for spark when the engine won't start, we get a nice hot looking spark out of the coil wire and out of a spark plug wire. The carburetor has been rebuilt with a new float, needle valve and seat, all adjustments made and a new fuel filter and spring. When the engine won't start we check for fuel in the carburetor and see plenty. A few pumps of the accelator pump delivers good steady streams of fuel. The points and condenser have been replaced, the dwell and timing set to factory specs. The distributor has been checked to determine if the mechanical advance weights work and they do. We have replaced the ignition coil, the engine has good quality, almost new spark plug wires. Both engines in the boat can run off of the same gas tank and the other has no problems. The batteries in the boat are new this season and they have a charge of 12.9 volts at rest. The charging system is working to charge the battery. We have disassembled and cleaned every connection from the battery to the engine including coil connections, starter connections, ground cables and even checked the resistance of the positive and negative battery cables. We have done voltage drop checks on the connections and everything seems ok. One thing I have noticed is that the running voltage of the ignition coil seems to be be different on this engine compared to the other that works well. We are getting about 9 volts running voltage on the malfunctioning engine and the good engine seems to be running at 10.5 volts. The new coil is slightly different than the original which could explain the difference. Is there a ballast resister for the primary of the points or is the lead wire the resister. I didn't get a chance to check it for resistance. We have also checked the resistance of the points closed and it is almost zero. Sorry for the long post but I thought it would be good for you to know what I have already tried. Any suggestions would be appreciated.

Bob:

 

[maxxman04]

Re: '78 Mercruiser 305 Chevy Starting Problems

should have a ballast resistor on each motor i believe. maybe check choke as well.

 

[Bob K.]

Re: '78 Mercruiser 305 Chevy Starting Problems

Hi all, I'd be curious to see what everyone thinks about a problem I'm having with my boat. The engines are '78 Mercruiser 305 Chevys which are coupled to outdrives (I think that is the correct name for gear boxes which drive propeller shafts). One of the engines has a hot starting problem, when started cold it works fine although it takes a few cranks to get it going. After taking the boat out, docking it and shutting it off it will not restart while hot. It seems like the engine is flooded and we can't even get a pop out of it. So far we have done the following: checked for spark when the engine won't start, we get a nice hot looking spark out of the coil wire and out of a spark plug wire. The carburetor has been rebuilt with a new float, needle valve and seat, all adjustments made and a new fuel filter and spring. When the engine won't start we check for fuel in the carburetor and see plenty. A few pumps of the accelator pump delivers good steady streams of fuel. The points and condenser have been replaced, the dwell and timing set to factory specs. The distributor has been checked to determine if the mechanical advance weights work and they do. We have replaced the ignition coil, the engine has good quality, almost new spark plug wires. Both engines in the boat can run off of the same gas tank and the other has no problems. The batteries in the boat are new this season and they have a charge of 12.9 volts at rest. The charging system is working to charge the battery. We have disassembled and cleaned every connection from the battery to the engine including coil connections, starter connections, ground cables and even checked the resistance of the positive and negative battery cables. We have done voltage drop checks on the connections and everything seems ok. One thing I have noticed is that the running voltage of the ignition coil seems to be be different on this engine compared to the other that works well. We are getting about 9 volts running voltage on the malfunctioning engine and the good engine seems to be running at 10.5 volts. The new coil is slightly different than the original which could explain the difference. Is there a ballast resister for the primary of the points or is the lead wire the resister. I didn't get a chance to check it for resistance. We have also checked the resistance of the points closed and it is almost zero. Sorry for the long post but I thought it would be good for you to know what I have already tried. Any suggestions would be appreciated.

Bob:

I found out what the problem is thanks to a gentlemen who has has been fixing this stuff longer than me. These engines have resister wire going to the ignition coil to reduce the battery voltage to the points when the engine is running. This resister wire is by-passed when the engine is cranking because the load on the starter drops the voltage present significantly so the coil needs all it can get for starting. Full batery voltage is given to the coil through the starter solenoid when the starter is cranking. A simple voltage test revealed proper starting voltage to the coil when starting the engine cold but as soon as it warmed up the voltage to the coil during starting was significantly reduced, preventing the engine from starting. We took the solenoid apart and the contact which supplies the full voltage to the coil was corroded. Live and learn.

Bob