Mercury outboard 140 spark issues

[ristovski1991]

Hello everyone i am new to this forum and new to boating. I tried looking through this forum and others to resolve my issue on my outboard. I believe i have a 77 merc 140 tower of power i cannot locate a nameplate anywhere on this motor. I was only able to find a few numbers on the block which are 8527738 and 62301. I suppose one of these is a serial numbe.
Anyway to get back to the problem i am having: with everything hooked up my motor is turning however i have a spark issue. When i do a spark test with a plug unscrewed connected to wire and held against ahe frame i only get one spark. Sometimes i get it when i am switching my ignition from on-off and off-on but no continuous sparking when motor is cranking. I already know my coil and control box are good as i conducted some tests that i found on youtube so i have continous spark when doing those tests. I also conducted a trigger test and i assume i did all those tests right and still the same problem when everything is hooked back up. Im willing to take any advice.

 

[Chris1956]

OK, Merc did not make a 140 HP motor in 1977. Merc made one in 1978-1979 1/2, and an older one in the early 70s.

As long as you have battery-driven CDI igniton with the one coil and a distributor, the troubleshooting is the same.

What shape is the wiring on the engine and boat harnesses? You must have continuous +12VDC on the red wire on the switchbox. You also must have power on the white wire of the switchbox, when the ign key is on. I would jumper both the red and white wires from the battery cable on the solenoid to remove the boat harness from the equation. Now run the spark test from the CDI Electronics web site. That will prove the coil and switchbox are good. If you still have intermittent spark, it is likely the trigger is bad.

 

[ristovski1991]

This is what i have. The wiring harness seems to be in a good condition however i will try these tests today and will post an update

 

[Chris1956]

Looks like you have the older brown/orange coil. That makes the motor from the early 70s.

However, the wiring harness looks to be newer, maybe 80s. See if you can wipe off the dirt on the switchbox so you can see the original colors on it, as your wiring harness colors will make it difficult to diagnose.

 

[ristovski1991]

Ok so here i am again doing a spark test but now i am jumping red and white at the switchbox and i am still getting no spark when cranking the engine. Now what i found interesting was when i was jumping the white and red terminal i was getting continuous spark at the removed spark plug without cranking. Still getting spark when switching ignition from off-on and on-off and rapidly turning my key. On the harness there is an orange wire which is connected to the ignition but is not connected anywhere on the motor it is insulated. Is that wire supposed to connect somewhere? I already did the switchbox test i am getting great spark. Also is there a good way of testing the trigger? Its difficult to search the forum for answeres because i dont know the year.

 

[merc850]

Have you looked in the dist. cap maybe the rotor is cracked or the contacts are corroded; there's a timing belt under the flywheel and it turns the distributor, when you take the cap off see if you can turn the rotor gently - if it turns around the belt is ruined. Fig. 3 shows the belt and dist. pulley.

 

[Faztbullet]

The trigger is bad........

 

[ristovski1991]

I will try to take the top plate off to see whats going on in there. I cleaned all the contacts already on the distributor but as Fatzbullet says the trigger might be bad. Is there a way to repair the trigger or has to be replaced?

 

[ristovski1991]

Ok so the belt is fine because the rotor doesn’t spin freely, and at the same time i conducted a spark test with the belt off and jumping red and white terminal with 12v at switchboard. According to a youtube video i should be seeing spark at the coil wire if i am spinning the rotor wit the belt off. I am not getting any. So now i have the whole trigger assembly out. Is there a way to repair this thing or has to be replaced?

 

[Chris1956]

You are going to identify the year of the motor, to make sure you get the right trigger. It is likely the trigger/distributor assembly needs to be replaced together,.

Get the block part number, of see if she has a silver, round plug with a number on it. These can lead you to find the correct year of the motor.

 

[ristovski1991]

These are the three numbers on the block that i can see 8527738, 62301 and 7408 and i am not sure which plug you are referring to.

 

[merc850]

The serial Nr. should be on the plate between the clamps. The blue switch is to cut off the ignition if the motor is knocked out of the water. I've found the serial range 3293234 thru 3502805.

 

[Faztbullet]

You are going to identify the year of the motor, to make sure you get the right trigger

There is only one trigger that fits 1970 thru 78-1/2 engines, same trigger fits 4 cylinder just disk is different. They made a odd ball trigger (horseshoe) but you cant find them anymore. CDI # 134-3736

 

[ristovski1991]

The serial Nr. should be on the plate between the clamps. The blue switch is to cut off the ignition if the motor is knocked out of the water. I've found the serial range 3293234 thru 3502805.

There is no label there or anywhere on the motor with a serial number on it. I cleaned up the distributor/trigger which i pulled out and there is a part number 393-3736 AA. I did some digging online and an ebay post came up where this person charges you $150 to repair your own trigger. What he does is just replaces the three wires after removing the rubber grommet i suppose as far as he can reach inside. He also states that the trigger is perfectly fine its just the rotten wires that are causing the problem. It sounds convincing because my wires on the trigger are in very bad shape insulation was breaking. I belive my white wire as making contact with ground somewhere around the grommet. So far i removed the grommet and cut the old wires as close to the body ad i could and added new wires with new terminals. Next i will squirt some epoxy to hold the wires in place and will connect it to my switchboard to see if anything has changed. I will post an update once I test it. Thanks for your inputs

 

[merc850]

I tried that on a dead trigger you have to remove the rubber grommet and use a small ball tool on a Dremel hand grinder to clear out the epoxy in the end of the chamber then, solder some new wires onto the 3 posts. I did this just to see what is in there. On my motor I have a new CDI unit.

 

[ristovski1991]

Nothing changed so far. Like i said i replaced the wires and there was no change. Next i took the trigger apart removed tge rotor and disk. Then I cleaned all the rust around the disk with wire brush made it nice and shiny. I cleaned up the sender as well. Replaced two bearings and snap ring. I just tested it and nothing changed again. I guess i will be looking for a trigger.

 

[ristovski1991]

Got some good news today. I found a trigger for 150 on ebay and replaced it today. Immediately I checked for spark and had great spark. After a few tries it started!! I whink my idle is set a little high but i might be wrong. I didn’t run it for long because i noticed it is not draining water out of the little side hose. Is there a water pump that delivers water to the motor that might be bad or stuck? Thanks fellas