1974 Mercury 650 - No spark

[Cohoho]

So I bought this old boat a couple months ago from a guy who said the motor wouldn't spark. I found that it sparked fine, and with new fuel and a little TLC/elbow grease, it ran fine. The last three times out it has run perfectly - started right up on the second or third crank, warmed up nicely, got me up on a plane with no complaints. <br /><br />So I set the boat up for fishing, with a fishfinder and a couple of manual Scotty downriggers. I spent some money at the tackle store and got the rods set up for blackmouth here in Puget Sound. My buddy and I (and two six-year-olds) head out bright and early this AM, and the dang thing won't start. Seems to be getting fuel just fine, so I check with my little light-up spark tester and no spark. <br /><br />What could have happened in a week of sitting to make a motor go from running perfectly to not running at all? I'm looking for a list of likely culprits and specific ways to confirm or eliminate each of them as the source of my problem. <br /><br />I am not a mechanic. I don't take the attitude of rebuilding or replacing major components because they MIGHT be the problem. I want to try to figure out what the problem is and then fix exactly that. <br /><br />Any guidance would be greatly appreciated.<br /><br />(edit) Oh yeah, if the guy who sold this to me was right about no spark, this might be an intermittent problem. Does that narrow it down any or just make it that much harder to diagnose?

 

[Yepblaze]

Re: 1974 Mercury 650 - No spark

If you want to fix it yourself you will need to become a mechanic. With electrical expertise. If that aint gonna happen, someone else will be needed.<br /><br />Perhaps during the time it does not spark it is easiest to troubleshoot, rather than having an intermitent problem.<br /><br />Thjere is a site on the web that will tell you procedure but it takes a special electrical meter and perhaps a schematic.<br /><br /> http://www.homestead.com/dolphinmarineservice/Tech.html

 

[KIWI MERCMAN]

Re: 1974 Mercury 650 - No spark

Sea lemon<br />It'll be your trigger, all these old ones do it sooner or later, It'll only take them an hour to change max, but most likey 5 to find. just kiddin.<br />Bet you thats your prob<br /><br />KIWI<br />RTFM

 

[Cohoho]

Re: 1974 Mercury 650 - No spark

Thanks Yepblaze and Kiwi,<br /><br />Kiwi, is the trigger also known by another name? Might be a dumb question, but I don't find "trigger" in my manual.

 

[KIWI MERCMAN]

Re: 1974 Mercury 650 - No spark

Sea Lemon<br />On that model the trigger is molded into the housing of the distributor under the cap, they need to replace the housing complete, and if you get this done get them to renew the 2 rollar bearings inside at the same time.<br /><br />Kiwi<br />RTFM

 

[Cohoho]

Re: 1974 Mercury 650 - No spark

Update on my "problem": I talked to the mechanic today about all of your suggestions. He said he could test various components, but I should try and fire it up before I brought it in. So I did.<br /><br />The battery that I cranked it with yesterday is pretty dead (that's the smaller trolling battery, just because it fits in the plastic battery case). So I connect the extra battery (a bigger one, also marine deep cell), and the motor fires right up. Is it possible that the small battery could have enough juice to crank the starter off and on for fully 20 minutes and not have enough juice to create spark for the plugs? Right now that's my operating theory, but it's not certain of course.<br /><br />I never make diagnosing easy, so there are a couple of other possibilities. I found that the coil wire has a little damage to the insulation (possibly caused by gas dripping out of the carbs after shutdown) and I fiddled with it before trying to start the motor today. Also, there is still the possibility of an intermittent problem that happened for the guy I bought the motor from, didn't happen for me for weeks, happened yesterday and not today. <br /><br />I plan to replace the coil wire just for peace of mind. Also the gas line between the tank hose connector and the fuel pump, which shows signs of deterioration. I certainly feel that easy repairs that look like possible future problems should be fixed before they leave me stranded. <br /><br />Thanks for all your help, and I am still interested in hearing your input. The problem has not convinced me that it is gone, so I will keep you all posted.

 

[KIWI MERCMAN]

Re: 1974 Mercury 650 - No spark

Sea Lemon<br />They are a 12v ignition system on that model, but its unlikely that your battery can crank your engine for that long and not have enough to start it.<br />These are the very things that a bad trigger does, I have replaced 100,s over the years and the only thing that most have in common is that they will work today and not tomorrow.They might run for 2 weeks then not, they might run for 2 hours then stop. <br />It is due to the vibration they have to put up with in that housing and the components fail.<br /><br />Dont let any one tell you that you cant have an intermitent CD ignition problem, you can!<br />Stators, power packs and triggers can all stop and start. Later model triggers are not so bad and tend to be either good or bad.<br /><br />I suggest that the next time it will not start, (maybe try it each day) if you can, take an old spark plug with you and take off one spark plug lead and check to see if there is any spark at your leads.Connent the spark to your engine block with a jumper lead and crank the engine. If no spark then a least you know that you have a ignition problem.<br /><br />Kiwi

 

[upstate]

Re: 1974 Mercury 650 - No spark

might want to test rectifier while yur at it sounds like it's not chargin yur battery while you are running

 

[SpinnerBait_Nut]

Re: 1974 Mercury 650 - No spark

Just a follow-up to KIWI MERCMAN's comment about the jumper lead. They make a nifty little tester that hooks to the plug and then your wire hooks to it. When you crank the engine, if it is firing, then this devise lights up. If no spark, no light. Works for me.

 

[mellowyellow]

Re: 1974 Mercury 650 - No spark

yes, an under-charged battery will get close to<br />starting, but won't. would be easy enough to eliminate... <br />upstate mentioned testing rectifier.<br />good idea! about $30 bucks? . it charges<br />battery and sends a signal to the Tach. (if u got 1)<br />good luck,<br />M.Y.

 

[Cohoho]

Re: 1974 Mercury 650 - No spark

I'm hoping that the battery is it, because that's easy to manage. I always hope and pray for the easy fix, and sometimes I get lucky.<br /><br />As for the rectifier, I will test it but I think I am charging my battery when running at decent RPMs. The last time I had the boat out was in the ship canal (no wake), so I was putt-putting around for an hour and a half. The time before that, I was out cruising I had no problem starting it up after. My new fishfinder will read voltage at the battery, so I should be able to tell if it's charging (I figure if I read 12.4 volts, the battery is being charged, correct??).<br /><br />I am swinging it by the mechanic today to test what he can and to show me what to check if it acts up again. I am also getting a coil wire and fuel hose replaced that look suspect. He said the trigger is a $300 part plus a fair amount of time to replace, so I am really hoping that ain't it.