'73 650 3cyl - No spark

[pwpeterson]

I have a 650 3cyl,serial 3661133 that has no spark.<br /><br />I bought the boat and motor last year and it ran a bit rough with no top end. I rebuilt the carbs this winter.<br /><br />When I first tried to start it this year I wasn't getting any spark. Spent several days staring at it and checking all connections. Decided to change the timing belt as it was in very poor shape.<br /><br />Still wasn't getting any spark after changing the belt. I let it go for acouple of days and came and tried it again. This time it started to backfire. Great! I just need to adjust the timing which I did and it started and idled well.<br /><br />Tried to start it three days later and no spark again. I have the dealer's repair manual but none of the testing equipment. I thought maybe the timing belt slipped so I re-installed it again to the manual's specs. I would be happy again to hear it backfire. <br /><br />How do I troubleshoot this?

 

[Laddies]

Re: '73 650 3cyl - No spark

Firsty ck for voltage on the red wire at the box then make sure the red wire on the box and the white wire on the box have the same voltage with the key on, if they do try turning the engine over with the starter and see if they remain the same this will tell if it's a engine or harness problem let us know

 

[pwpeterson]

Re: '73 650 3cyl - No spark

Laddies, Thank you for taking the time to respond to my post. <br /><br />Per your instructions I checked the red, white and brown wires...<br /><br />Red always 12.8 volts.<br />White always 12.8 volts with key on.<br />Brown nothing with or without key on.<br /><br />I found the following from another post...<br />-------------------------------------------------<br />If you have a testlight or voltmeter check the following on the switch box.<br /><br />1) 12 Volts on the red terminal at all times.<br />2) 12 volts on the white terminal with the key in the "ON" position<br />3) 12 volts on the brown terminal with the key in the "ON" position. If low or nothing on this one the mercury tilt switch is faulty.<br />-------------------------------------------------<br /><br />I disconnected the mercury tilt switch and still nothing.<br /><br />What's the next step?

 

[Laddies]

Re: '73 650 3cyl - No spark

The haresses is Ok,next diconnect the mercury switch from the switch box, voltage on the white black trigger wire must be a least 9V, with the wire hooked up and cranking the engine, next with a DVA you must have 3 volts between the black and the blue trigger wires with them hooked up, a low reading here means a bad trigger,if thats OK with a DVA ck the green wire to the coil it should be 100+ volts if none or low you have a bad switch box. With out a DVA hook a jumper between the blk/white and blk trigger wires and arc the blue post if you have fire its the trigger if not it's the box--Bob

 

[pwpeterson]

Re: '73 650 3cyl - No spark

Thanks again, Laddies.<br /><br />What's a DVA? I do have a multitester. Will that do the job?<br /><br />Also, what and where is the 'trigger'?<br /><br />Thx<br /><br />pwp

 

[Laddies]

Re: '73 650 3cyl - No spark

A DVA is a meter or meter adtapter that allows you to read peak voltage most outboard ign. tests require one today the trigger on your motor is part of the dist. hsg. and has 3 wires running from it to the switch box, blue, blk and white blk--Bob

 

[pwpeterson]

Re: '73 650 3cyl - No spark

This is getting frustrating...<br /><br />I went out to do the second set of instructions. I performed the first set again just to make sure I did them right. This time I couldn't get anything from the white wire with or without the key on.<br /><br />I had disconnected the tilt switch so I connected it again and still nothing on the white.<br /><br />I turned the engine over for a second and tested it again. This time there was 12 volts on the white wire when the key is on.<br /><br />I thought it might have something to do with the connector that attaches everything to the engine. (The wierd' shaped one with 8, 1/8" pins and runs from the merc control.)<br /><br />I cleaned both female and male ends thoroughly and reconnected it. Ran the tests again and now I don't get anything from the white wire regardless if I briefly turn the engine over.<br /><br />I did try the first step of the second set of tests. (...disconnect the mercury switch from the switch box, voltage on the white black trigger wire must be a least 9V, with the wire hooked up and cranking the engine, )<br /><br />There was no voltage on the white/black wire when the engine was turned over.<br /><br />Your thoughts...<br /><br />pwp

 

[andyhoss]

Re: '73 650 3cyl - No spark

pwp,<br /><br />i am going through similar problems with my 650 4 cylinder... trying to figure out why there is no spark and such... i must say if you are not consistently getting 12 volts to white (ignition) wire.. and sometimes none at all you need to eliminate that problem first.. short in internal/external wire harness...don't really know what else it would be....

 

[andyhoss]

Re: '73 650 3cyl - No spark

also and this may be obvious, but if you have no voltage in the white wire I don't believe you will have anything in the white/black wire (trigger test)

 

[pwpeterson]

Re: '73 650 3cyl - No spark

Here's a downloadable troubleshooting guide I found that appears to provide some insights. http://www.rapair.com/Default.aspx?tabid=90 <br /><br />I will let you know how it goes.

 

[andyhoss]

Re: '73 650 3cyl - No spark

thanks for the great reference pwp... i'm putting a new switchbox/coil in my boat and that will come in handy if anything else goes wrong.... im a little concerned about the fact that the book says ignition systems are not very good on the 1970-1971 mercs and that you should upgrade to the ignition thats worth as much as my engine....also I'll have to do the battery test on 3500 rpms to see if the voltage is between 12 and 16 volts.... anyways I tried to help you and I think you helped me more<br /><br />thanks a lot<br />Andy

 

[pwpeterson]

Re: '73 650 3cyl - No spark

If I need a new switch box can anyone recommend which one I should get... Rapair's (www.rapair.com) or Grubbs's (http://www.oldmercs.com/ignsys.html)?

 

[andyhoss]

Re: '73 650 3cyl - No spark

im getting grubb's today ill let you know how it goes

 

[andyhoss]

Re: '73 650 3cyl - No spark

I'll tell you what I got the one from grubb's today installed and she started up like a champ<br /><br />I have to say im not to impressed with how it was packaged and the information that came with it ....<br /><br />but if the part works good than who cares right..

 

[pwpeterson]

Re: '73 650 3cyl - No spark

Ahoss,<br /><br />How much did you pay for it? <br /><br />What year and model is your engine?<br /><br />Was the problem no spark?

 

[andyhoss]

Re: '73 650 3cyl - No spark

yes no spark.... the part was $240 replaces the coil and switchbox... my engine is 1971 mercury 650 4 cylinder.. <br /><br />be sure to cover that troubleshooting guide on the link you posted it has it spot on... really couldn't be explained any better!<br /><br />did you take care of the problem you were having registering 12 volts on the white wire into the switch box with the key in the on position??<br /><br />Andy

 

[pwpeterson]

Re: '73 650 3cyl - No spark

Andy, <br /><br />My guess right now is I have a bad harness. There is some insulation that is falling off a couple of wires. I taped over them but I think I should get it replaced. <br /><br />I hope this fixes the problem. <br /><br />Paul

 

[andyhoss]

Re: '73 650 3cyl - No spark

sounds like a good bet at this point replacing it will be a breeze<br /><br />good luck

 

[pwpeterson]

Re: '73 650 3cyl - No spark

I opened up the internal harness and checked all the wires for breaks, chips etc. They were ok.<br /><br />I resoldered the key switch connections after I discovered the red's connection was loose.<br /><br />Put it all back together and now I seem to keep 12 v consistently on the white wire, but still no spark. <br /><br />Nothing on the brown wire.<br /><br />I disconnected the tilt switch from the black/white terminal. With the key on I get 12 V on the black/white wire.<br /><br />Still no spark.<br /><br />When I reconnected the tilt switch it drops down to 3 volts.<br /><br />Does the tilt switch need to be connected to get a spark? <br /> <br />Is it my tilt switch causing the problem?<br /><br />pwp

 

[pwpeterson]

Re: '73 650 3cyl - No spark

Here's a more detailed test...<br /><br />The next time the engine does not start, <br /><br />1. Take a DC voltmeter and check the voltage on the White terminal of the switch box(12V from the key-switch). You should have at least 9-1/2 volts at cranking. Low voltage, check the wiring, battery and key-switch <br /><br />2. Take a DC voltmeter and check the voltage on the Red terminal of the switch box(12V from the battery). You should have at least 9-1/2 volts at cranking. Low voltage, check the wiring and battery.<br /><br />3. Take a DC voltmeter and check the voltage on the White/Black terminal of the switch box (12V through the switchbox to the trigger). You should have at least 9 volts at cranking. If the voltage is ok above and low here, replace the switchbox.<br /><br />4. Disconnect the White/Black, Blue and Black trigger leads.<br /><br />5. Connect a jumper wire from the White/Black to the Blue wire.<br /><br />6. Connect another jumper wire to the Black wire.<br /><br />7. Bring # 1 cylinder to approximately TDC (Top Dead Center).<br /><br />8. Connect a spark gap tester to the # 1 spark plug wire.<br /><br />9. Turn the key-switch to the on position.<br /><br />10. Tap the jumper wire you connected to the Black wire against engine ground. You should get a spark each time you do this. If you get fire, the trigger is likely bad.