No spark on on '74 150hp. I'm new to Merc's...Help!!

[BoatingCop]

Serial #43200823. Is this a '74? So I got my boat, and it seems it's not getting spark. Where do I begin to trouble shoot? I've read sothing about a switch box causing issues. What about cap and rotor? Also, do these engines take special plugs? I pulled the plugs and they look diffeent than normal ones, as there is no "prong" to gap. Any pointers? Thanks!!

 

[BoatingCop]

Re: No spark on on '74 150hp. I'm new to Merc's...Help!!

I just checked some wires for voltage. The red wire going into the distributor cap has 12v when the key swithch is on. That would tell me that the distributor has voltage. I couldn't find any voltage on the coil though with a voltage meter. Also, I checked out the CDI Electronics web site but the earliest engine they cover is 1978 and they talk about a dual switch box. Is mine a dual switch box?

 

[gwukena]

Re: No spark on on '74 150hp. I'm new to Merc's...Help!!

Check page 67 of cdi t/s guide, I believe your engine is battery cd ignition without points not adi.

 

[CharlieB]

Re: No spark on on '74 150hp. I'm new to Merc's...Help!!

The switchbox on your motor is specific to the distributor ignitions, the red wire should have a constant 12 V and the white wire should also have 12 V when the key is ON, if no voltage on BOTH of these wires check the fuse, ignition switch and the terminals in the large cannon plug that connects the boat wiring to the motor, corrosion or too loose fit can cause a problem.

CDIElectronics has an excellent Ignition Troubleshooting Guide available for free download on their Support pages. Get it. It will lead you thru any and all tests to accurately diagnose any problem with your ignition.

 

[BoatingCop]

Re: No spark on on '74 150hp. I'm new to Merc's...Help!!

Ok, well the strangest thing happened. I found that while I was cranking the engine, I did not have the warm up lever advanced all the way. I advanced it, and BOOM! It started! It ran smooth and perfect. I ran it for about an hour in a barrel after initially running it on a flusher. I do have one issue though. It seems to be idleing high. How would one adjust the idle? Heres the video.
http://youtu.be/ydKW7L5fIBk

 

[mercuk]

Re: No spark on on '74 150hp. I'm new to Merc's...Help!!

I'm gona guess that when you pulled up the advance lever, the cables are just a bit sticky and didn't fully disengage the warm up lever's throttle increase.
Check to see where the throttle cable goes into the engine and I bet you can move it back down to reduce the rpm's. Just stiff throttle cable I rekon.

 

[BoatingCop]

Re: No spark on on '74 150hp. I'm new to Merc's...Help!!

I just took it to the lake to see how is would perform under a load. I got to the ramp, and cranked and cranked and cranked but it would not start. Plenty of fuel running into the water but no spark. What could cause the intermitent spark problem? Its either all or nothing.

 

[Chris1956]

Re: No spark on on '74 150hp. I'm new to Merc's...Help!!

The intermittent spark could be caused by a failing trigger. Go on the cdielectronics web site and look for the ignition test for the battery powered CDI ignition, that you have. The test will prove that the rest of the ign system is good, therefore the trigger is bad.

Before you test or replace anything, make sure you have +12VDC on the red and white wires on the switchbox. On those old motors, the motor wiring harnesses go bad and if you have no power to the switchbox, you will not have any spark.

 

[aussieflash]

Re: No spark on on '74 150hp. I'm new to Merc's...Help!!

Did you pull plug and check for spark while it refused to start??Im guessing spark is fine.
Id first be looking at Choke/solenoid operation and/or possible flooding due to carbs (stuck needle,saturated or damaged float or dirty jets etc)

 

[BoatingCop]

Re: No spark on on '74 150hp. I'm new to Merc's...Help!!

The intermittent spark could be caused by a failing trigger. Go on the cdielectronics web site and look for the ignition test for the battery powered CDI ignition, that you have. The test will prove that the rest of the ign system is good, therefore the trigger is bad.

Before you test or replace anything, make sure you have +12VDC on the red and white wires on the switchbox. On those old motors, the motor wiring harnesses go bad and if you have no power to the switchbox, you will not have any spark.

I went around with the multi-meter and it shows 12v on the red wire going into the distributor. No power to the white wire that goes into the dist tho. I'm doing this with key on. I also have no voltage going to the coil (grey wire) with the key on. I followed this to the starboard side of the engine where it hooks to the top terminal of the terminal block (Not sure thats the right terminology). Should the coil wire have 12v with the key on? BTW...the motor turns over strong and the neutral safety swithch works too. Is the switch box yall refer to the remote contol box? Thanks for all the help. These Mers are a different animal to me.

 

[BoatingCop]

Re: No spark on on '74 150hp. I'm new to Merc's...Help!!

Just unhooked the mercury switch (or what I think was the merc switch). It was on the port side of the switch box mounting plate. It has a wire that goes to the switch box and one that grounds. Still nothing. I'm only getting power to that one wire going into the dist.

 

[merc850]

Re: No spark on on '74 150hp. I'm new to Merc's...Help!!

Here's a diagram for wiring purposes - the distributor has contacts and a rotor, undo the bolt that clamps it to the housing to check for corrosion water etc. Do not try to remove rotor it is molded onto shaft! The ignition switch could be bad and/or harness plug not pushed on all the way if 12v not present at switchbox white terminal.

 

[carholme]

Re: No spark on on '74 150hp. I'm new to Merc's...Help!!

As far as your s/n goes and trying to confirm your model year, you appear to have one too many numbers. Can you recheck the number?

Gerry

 

[BoatingCop]

Re: No spark on on '74 150hp. I'm new to Merc's...Help!!

Thanks for the diagram. I believe the key switch is working because I get 12v at the wire going to the dist with the key on and when I turn the key off, no more voltage. I'm hoping a connection from the motor to the remote control. It just happened like flipping a switch though. It wouldn't fire, then all of the sudden it fired and ran for an hour, and now I'm back to nothing. Thanks for all the help. Keep the suggestions coming.

 

[merc850]

Re: No spark on on '74 150hp. I'm new to Merc's...Help!!

I had the same kind of problem on my 850, if there is power to the SB and motor won't spark then do the trigger test. The wires on that type screw into the cap but usually don't need replacing 'cause they're solid wire not resistor type. The spark plugs are Perma Gap type that fire around in a 360* circle and if they are in good condition, last for a few years.

 

[aussieflash]

Re: No spark on on '74 150hp. I'm new to Merc's...Help!!

Ok, well the strangest thing happened. I found that while I was cranking the engine, I did not have the warm up lever advanced all the way. I advanced it, and BOOM! It started! It ran smooth and perfect. I ran it for about an hour in a barrel after initially running it on a flusher. I do have one issue though. It seems to be idleing high. How would one adjust the idle? Heres the video.
http://youtu.be/ydKW7L5fIBk

So you fully opened carb throat and she started and ran smooth for an hour.......Doesnt sound like spark issue...sounds like starting procedure issue or fuel related issue...sorry im repeating myself...ill go away now...good luck.

 

[CharlieB]

Re: No spark on on '74 150hp. I'm new to Merc's...Help!!

The Red wire on the switchbox should ALWAYS have 12 V.

The White wire should turn ON and OFF with the key switch, if it does not you have a problem, either the key switch or poor connection.

Once you get this sorted out THEN you will learn that the stacked 6's like a lot of choke to get started, once started, there ain't nothin sweeter!

 

[merc850]

Re: No spark on on '74 150hp. I'm new to Merc's...Help!!

The white wire to check is on the opposite side of the distributor and with a bad trigger it will run sometimes then stop then go etc.