Mid 1970's Merc 1250 starting issue.

[jblaze2556]

So this is my first time posting on here. I have had some issues with a boat that I just bought getting started.

The day I bought the boat, the gentleman I bought it from started the boat right up for us with a garden hose attached to the motor. No big deal and the motor fired right up. He kept his battery and I bought a new one. When we got home, we decided to take a look at why we were told the motor was running slightly rough. To see if we needed spark plugs or anything else. We put the new battery in with a minor hiccup. When we connected the cables they accidentally got crossed. Red for black. I know a dumb mistake. Luckily we didn't do anything and noted the mistake within a few seconds. We swapped the cables and attempted the start the boat. With no luck. It will crank but will no longer turn over. I have chased wires, shooting voltage from the battery to the motor, to the distributor, to the ignition. We are getting fuel, air, and no spark. Can anyone lead me in a direction that a young individual that made a new boater mistake can possibly fix in 2 short days? I do not have a repair manual as I hav not been able to find an exact one for my particular motor. Everything is getting good voltage and grounding properly, so I am not sure where to start. I was thing the distributor may have been fried but I am not sure I can find the parts or a new one before the weekend. Any help will be much appreciated.

Thanks,
Drew

 

[Faztbullet]

Sound like you fried switchbox or trigger.. here is testing....

Mercury
Battery CD Ignitions without Points
Three Cylinder Engines
332-4796/393-4797 Type Ignitions
•SERVICE NOTE: Check the battery voltage at approximately 3500 RPM, MAXIMUM allowable reading is 16 volts and minimum is 12V. Running below 12V or over 16 volts will damage the ignition. Check for loose connections or a bad battery. Maintenance free batteries are NOT recommended for this application.

General:
1.Clean all battery connections and engine grounds.
2.Disconnect the mercury tilt switch and retest. If the ignition works properly, replace the mercury switch.
3.Connect a spark gap tester to the spark plug wires and check for fire on all cylinders. If some cylinders fire and not others, the problem is likely in the distributor cap, rotor button or spark plug wires.
4.Perform a voltage drop test after the engine is repaired to see if there is a problem with the voltage going to the CD module. At cranking and while the engine is running, use a DC voltmeter and put the black meter lead on the battery POS (+) post and the red meter lead on the positive battery cable at the starter solenoid. Keep the black lead on the battery post and shift the red meter lead to the positive post of the rectifier, then to the red and white terminals on the switch box. If you find a reading above 0.6V, there is a problem at the point where the voltage jumped up. For instance, if the meter reads 0.4V until you get to the white terminal and then jumps to 2.3V on the white terminal –this indicates a problem in the keyswitch, or harness. Repeat the test for the negative battery post by putting the black meter lead on the battery NEG (-) post and the red meter lead on the negative battery cable terminal, then shifting to the engine block, rectifier base and case ground of the CD module.

No fire at all:
1.Connect a spark gap tester to the high-tension lead coming from the ignition coil and set it to approximately 7/16". When you crank the engine over, if it fires while the spark gap tester is connected to the coil and does not fire through the spark plug wires - there is a problem in the distributor cap, rotor button or spark plug wires.
2.Check the DC voltage present on the white and red terminals while at cranking. It MUST be at least 9? volts. If not, there is a problem in the harness, key switch, starter battery cables or battery.
3.Check the DC voltage on the white/black trigger terminal at cranking, there must be at least 9V available with the trigger wire connected.
4.Check DVA voltage between the blue and black trigger wires (They must be connected to the switch box). You should read at least 3V. A low reading indicates a bad trigger.
5.Check DVA voltage on the green wire going to the coil, it should be over 100 volts at cranking.

Only fires when you let off of the keyswitch:
1.This symptom usually indicates a bad trigger or low voltage.

No fire or intermittent on one cylinder:
1.Connect a spark gap tester to the high-tension leads coming from the distributor cap and set the gap to approximately 7/16".
2.Align the rotor with #1 spark plug wire. Disconnect the trigger wires and connect a jumper wire from the white/black trigger terminal to the black trigger terminal on the switch box.
3.Connect another jumper wire to the blue trigger terminal turn the ignition switch on. Strike the jumper wire from the blue terminal against engine ground – (DO NO HOLD THE JUMPER AGAINST ENGINE GROUND!). (Or use a CD Tester). Only the #1 spark plug wire should fire. If another spark plug wire fires, there is a problem in the distributor cap.
4.Repeat the test for the other cylinders.

 

[Chinewalker]

If it's a 1250, it is NOT mid 1970s. It would be 1968 or 1969.

Good chance you popped the rectifier when you crossed the wires, although that likely wouldn't cause the starting issue you're having...

 

[jblaze2556]

It was an electrical switch box. Problem resolved thanks for all the help.

 

[emckelvy]

Be sure to check your rectifier output because even the shortest time with batt connections swapped, it almost guarantees a blown rectifier. Your ignition requires a "hot" battery to work properly, and will quit, be damaged, or fail to start if voltage is low because of a malfunctioning charging system.

A simple check of battery terminal voltages with a digital meter will do. When you raise the fast idle lever to increase engine speed, you should see a rise in voltage.

Note that you're not gonna get full charging output (approx 10 amps) out of the engine's charging circuit until you reach at least 2000-2500 rpm. But don't do that on a flusher, it's not good to rev up an engine with no load or exhaust restriction. Some motors will tolerate it better than others, but no sense in tempting fate!

If the rectifier is blown, you can replace it for less than $5 by installing a generic bridge rectifier. You'll just need to re-do the connections to the new rectifier, and provide an additional ground wire (the new rect has a separate terminal for ground, whereas the original Merc rect is grounded via its case).

Here's a cheap rectifier on eBay: http://www.ebay.com/itm/251483712332

HTH.............ed