TOPIC: '72 Merc 650 3 CYL No Spark

Hi all,

Well after a long winter off it is time for me to get back to the frustration and hair pulling of restoring old motors/boats I pick up in the spring.

The Motor: Its a 1972 Mercury 650 which is a 3 CYL and the ignition is Type III Thunderbolt - Distributor C.D. Ignition -Pointless.

It's on a mid-70's Glastron and has not run in a long time. The Starter was removed and sitting rusty in pieces in the glove box.

Initial progress:

I put a replacement starter in and got it cranking.
- first thing I checked compression....good all 3 about 125.
- hooked up water hose...squirted premix in cyls and it fired.
- choke solenoid hot wire was rotten so I jumped it to get choke.
- plastic throttle actuator was broken so I wired the carb throttle a little advanced for starting.
- got it running though had to keep activating choke to keep it running (yea old dirty carbs).

Now I am pretty happy.

Next Steps:
- removed the carbs and thoroughly cleaned.
- while I was at it I noticed a lot of internal wiring with the typical cracked and fallen off insulation etc so I removed the whole harness and spliced new wires when necessary and taped up others that were cracking.
- Put it all together and in high anticipation of a smooth running motor after a carb cleaning....NO SPARK!!!! ARGH!!!

Troubleshooting:

Now here is where the frustration comes in.

I am very confident that I rewired everything correctly( I have restored lots of old mercs and have wiring diagrams and shop manuals etc) so I figured it must me an issue with one of the wires I spliced/fixed.
-started by checking continuity at all pins on internal adapter to wire ends and all is fine.

Now the search begins....

1) Switch Box Diagnostics using CDI instructions.
-first determined that I had 12v to red terminal always and to white when key was turned to on.
- did the jumper test to rule out various things.
- removing trigger wires( white/black, black, and blue) I jumped white/black and black terminals on switchbox. Turned key
to on and jumped jumped from blue terminal to ground(touching only) and as expected heard the coil snap.
- next step was to connect spark tester to #1 cyl ply wire, turn flywheel to TDC on cyl one and repeat. YES spark. Repeated for all 3 wires/cyls and had spark
Assumption... Switchbox, coil, and distributor should be ok right?

But still no spark.

Next I removed the distributor and when removing the stuck cap found the brush in the center of the cap broken(may have done it when prying the cap off)... I replaced with new. Inside of cap was dirty so I cleaned up including wire terminals and rotor etc.
BTW... the 3 trigger wires from the distributor to the switchbox seemed the best of any (although mostly covered in heavy insulation so I did not touch or replace any of them).

Still NO SPARK!!! ARG!!!

I am not sure what else to try. I don't have a fluke to test DVA etc.

Only other thing I can think of to mention is that it appears that the Mercury switch(that is normally connected to the same terminal on the switchbox as the white/black) is missing.

Sorry for the long story but I am open to any ideas that anyone can provide. Be glad to show pics of anything important to anyone.

THanks so much and glad to be back.

Tim.

there should be a mercury switch connected to the brown distributor wire that may be shorting to ground.

OK, from what I understand it passed the test in 1) with flying colors.

This means that the switchbox and coil are good. And that spark will travel from the coil, thru the distributor, rotor and plug wires, to all the holes.

So, that means besides coil and switchbox, your dist. rotor isn't shorted to ground, the distributor isn't arcing or doing other bad things, and your spark plug wires are good.

Test 1) is done to rule out things other than the distributor trigger.

Therefore, if you can get spark all the way thru to the plugs with the trigger bypassed, and it won't spark with the trigger reconnected, the trigger is bad.

Unfortunately, the trigger is encapsulated within the distributor housing and is nonreplaceable. You'll have to disassemble the dist and replace the housing. Renew the ball bearings at the same time, unless they are in like-new condition.

There's a bearing retaining snap ring in there that must be replaced, since they like to rust, break, then send metal bits flying around the distributor. Ask me how I know about this! Definitely a buzz-kill when the snap ring breaks and ends your day of skiing!

Sometimes you'll see good used dist assy's on eBay, since there are plenty of burnt-up 650-3's out there!! (hint hint replace the impeller every year on these!!).

Or check your local Craigslist, you may find a parts motor for cheaper than the price of a new trigger assy.

The Merc P/N 4797A 3 is an "obsolete" part and was over $464 when last priced.

CDI Electronics doesn't even make a new replacement trigger assy for this model (probably isn't enough demand, unlike Inline Fours and Sixes); but they will rebuild your old unit. You'd have to contact them for a price quote.

www.cdielectronics.com/AppGuide.aspx

Here's one I found on eBay by querying on the part number, hard to say if the trigger's good for sure, but at least it's cheap!



Here's another one for $72 shipped, the wires look good, and they claim it was pulled from a working motor:



At least that one has a 7-day exchange policy on dead electrical parts.

Anyway, HTH & G'luck........ed

p.s. the missing mercury switch would have nothing to do with the problem, it's only there to kill spark in case the motor hits a submerged object and goes flying up.

HOW IS THE TIMING BELT ?

Thanks Ed for the clear explaination and clarification that I am pretty clear with what I have found so far and it certainly looks like trigger issue. THanks also for the links to the parts on Ebay. One of them is actually here in Rochester so I hope I can avoid the shipping.

I'll give it a shot.

Dave... the belt is dry and showing cracks so I will need to replace...but it is tight and functioning now while I work on getting it running right.

I also figured out my rectifier is bad(after doing some of Dr F'Merc's tests.) It will have to be replaced but for now I just have it unhooked. I assume it is only for charging battery in this motor and wont affect starting?

THanks
Tim

barnfinder wrote:

I also figured out my rectifier is bad(after doing some of Dr F'Merc's tests.) It will have to be replaced but for now I just have it unhooked. I assume it is only for charging battery in this motor and wont affect starting?THanks Tim

Yeah, the ADI models can be affected by rectifier problems, but distributor igns won't be bothered by a blown rectifier (unless your battery voltage drops to nuthin' because of that!).....ed

Getting nowhere fast. Found a donor distributor and switch box. I switched out the distributor thinking it might be the trigger....No Spark. So I switched out the switchbox....No Spark.

Gonna do the CDI jumper test again to see if I can spark the coil and the plugs again.

Lost and out of ideas.

Progress. I picked up another used distributor that was in really rough shape(the cap that is....wires were cut off/yanked cause they didnt realize that they screwed out....cap was cracked bad and inside the brush was in pieces.)

BUT... I paired it with my cap and wires and threw it together and she had spark.

Ran out and got a new impellar and replaced and she started right up. Though without the controls on it was scrambling to keep it in neutral and adjust the throttle manually.

Hooked up the throttle and shift cables on the controls I was using to start it and it is racing like crazy so I shut it down.

Appears that the throttle cable is setting the the throttle linkage back to idle setting etc. about as far as it can go but it is still idling WAY too fast.

What might be causing this? Only thing that comes to mind is that I replaced the original coil in my process with a new coil I had that was from an 89 Merc Classic 40....that wouldn't do it would it?


BTW....it started racing when I first had it running without the cables on about the same time it jumped into gear(even with the throttle turned back manually to the idle stop.....if that helps?

I am excited to start tweeking the idle screws on the carbs etc but can't do much with it racing like this.

To set the timing pulley do I:
1) Do as I usually do....remove the cap on the distributor pulley and align the arrow on the pulley with the alignment mark on the flywheel OR
2) As my manual says: Observe the straight line mark on the flywheel and the plastic timing indicator(which btw is missing on this motor)on the crankcase. Align the cast tab on the pulley with the cast mark on the distributor adapter. (***NO mention here of the arrow on the pulley aligned with the mark on the flywheel***).

Thanks.

Tim

Ok now I am getting really frustrated. Got back to it now and I am back to having NO spark again.....without even touching it since last night when it was racing at idle.

I do have a complete parts motor I just picked up for it on Sunday so I think it is time to start by replacing the internal wiring harness that is in good condition as opposed to the ratty one I spliced and patched on this one.

I think the BIG question here is ...What would be a possible cause of intermittent spark. It first fired right up....removed/cleaned carbs and fixed rotten wiring harness. No spark. Replaced distributor and switch box....No spark...replaced with another distributor...Spark and run. Overnight ...no spark.