No Spark - 8HP Mercury 1989 2 Stroke - Are these Coil, Stator, and Trigger Readings Good?

Hello,

I'm working on a 1989 8 HP Mercury 2 Stroke that has no spark.

I haven't been able to find out what readings I'm looking for on the coil, stator, or trigger assembly for this motor. Keep in mind these reading are made while the parts are still on the motor. If I need to remove them to make the readings let me know.

Left Coil

Between Positive and Negative Terminals - 0.1 Ohm
Between Positive and Spark Plug Wire - 903 Ohms
Between Negative Spark Plug Wire - 904 Ohms

Right Coil

Between Positive and Negative Terminals - 0.1 Ohm
Between Positive and Spark Plug Wire - 972 Ohms
Between Negative Spark Plug Wire - 973 Ohms

Stator

Between the wires - 3.121k Ohms
Between blk/ylw and ground - 3.257 Ohms
Between blk/wht and ground - 135.7 Ohms

Trigger Assembly

Between the wires - 735
Between brwn/ylw and ground - Nothing
Between brwn/wht and ground - Nothing

Are these readings any good?


I read somewhere I could test the kill switches or kill switch wires, but the instructions were unclear. If anyone can guide me on how to work the wires in order to test the kill switches let me know.

I also read it could be the switch box, but there are zero instructions on how to test the switch box. Anyone know how to go about testing the switch box?


Also, is there anything else I can test for?

Your numbers above look right in range - they sound good.

To test the kill switch you can just place your leads on either side of the switch. In the "off" position you should have (effectively) NO resistance (when you switch to off the ignition power which would typically go to the coils/plugs is sent to ground so the motor is "killed") - with the switch ON, you should have "significant" resistance.

If you follow the wires in/out of the kill switch you should find one end is a bullet connector back at the switchbox. The other end runs to the engine block. You could simply unplug the (bullet) and measure between (that) and anywhere on the block that is well grounded and try your switch.

If you have a tiller model there is also a kill switch right in the end of the tiller handle. That one is a (momentary "on") that kills the ignition when you use your thumb to depress the end of the handle. If you look in the front of the cowl under the carb you will see the two wires coming from the tiller handle assembly. Testing those two wires should result in "significant resistance" until you depress the button (at the end of the tiller handle) and then there should be near zero resistance.

While you have done all the resistance tests the stator or trigger still could be bad (but unlikely). If in doubt you can have them tested using a DVA meter (or regular multi-meter with a DVA adapter) which will measure the actual voltage output. Both the stator and trigger produce AC so you need a (Direct Voltage Adapter) to convert it to a readable number in "DC" which the ignition runs on.

Based on what you have posted I would suspect that unless you find an issue in the stop/kill circuit that you have a toasted switchbox. But given that, that part is the most expensive of all the possible components, you do want to rule out everything else first. And that is the "test" for the switchbox - prove it is "nothing else", and then replace it.

Wow your response is probably the best I've ever received on any forum. Answering all my questions and then some with clear instructions and information. Thank you so much for taking the time!

I tested the on/off kill switch at the front of the motor and it performed as you explained.

I tested the kill switch on the tiller handle and it reads "significant" resistance (no reading) for when it is pressed or not. However, if I understand this correctly, that wouldn't be a problem with the spark as the act of grounding is what is killing the motor, correct?

If that's the case, looks like I will be trying out a new switch box.

Curious, is it possible that the timing could be the cause? I also haven't been able to find much on how to check the timing on this motor. Seems like Mercury didn't sell too many of these. Information is scarce.

Correct - if you have (massive resistance) on the tiller handle kill switch whether depressed or not, it is not functioning but it is also NOT killing the ignition.

No, the timing will have no effect on a "no spark" condition. If the timing was off even by say 90 degrees you would still "get spark" just totally at the wrong time - but it would not prevent the (ignition) from producing power (stator), rectifying/storing it (switchbox), releasing it (trigger - but at the "wrong" time compared to the piston location in the cylinder) and then sending the power to the coils and ultimately the plugs.

And actually, the 8 horse was exactly the same platform as the 6 and 9.9 (until 1994 when the 9.9 went to the same platform as the 15 horse). Once you get it sorted out and "firing" you can post again I will put up the "synchronization" for it which includes the timing. On the flywheel there is a couple (sets) of white dots. Those are the timing marks, so there is no (worrying about) degrees when timing these small portables.

galamb said:

Correct - if you have (massive resistance) on the tiller handle kill switch whether depressed or not, it is not functioning but it is also NOT killing the ignition.

No, the timing will have no effect on a "no spark" condition. If the timing was off even by say 90 degrees you would still "get spark" just totally at the wrong time - but it would not prevent the (ignition) from producing power (stator), rectifying/storing it (switchbox), releasing it (trigger - but at the "wrong" time compared to the piston location in the cylinder) and then sending the power to the coils and ultimately the plugs.

And actually, the 8 horse was exactly the same platform as the 6 and 9.9 (until 1994 when the 9.9 went to the same platform as the 15 horse). Once you get it sorted out and "firing" you can post again I will put up the "synchronization" for it which includes the timing. On the flywheel there is a couple (sets) of white dots. Those are the timing marks, so there is no (worrying about) degrees when timing these small portables.

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Great information. Thanks again. Just ordered the switch box. Fingers crossed!

Update! She runs now! Thanks for the help!

Can I pick your brain apart just a little bit more if you don't mind?

No water was coming from the tell tale or exhaust. Just ordered a new impeller kit.

I had it running for maybe about a minute or two because I forgot to connect the switch to ground and finally while panicking I was able to remember I could just remove the spark plug connectors. Would this have caused much damage to the motor? Anything to keep an eye out for?

Not recommended obviously but running for a couple of minutes should not have hurt anything except the impeller which you are replacing anyhow.

When you have the lower unit off to service the water pump you might want to try jury rigging up a hose to the water tube just to make sure there are no blockages in the tube, water channels etc. You should get basically unobstructed water flow at about the same rate as coming out of the hose.

With these small portables I occasionally give them a good (de-scale). Even freshwater run they can build up lime and other minerals. There is commercially packaged products but vinegar works well and is super cheap (there is "cleaning" vinegar available that is double strength).

With the lower unit off I simply stand the motor upside down and use a funnel to fill from the water tube. Pour in the vinegar until it starts coming out the exhaust and leave it (inverted) for a couple days. The acid in the vinegar eats up all the (crud) and is safe enough that it doesn't hurt any gaskets/seals etc. It's worth doing, especially while waiting for a couple days when parts are ordered and you have it torn down anyhow...

Not sure if filling an upside down motor with a fluid is a good idea.

galamb said:

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Perfect thanks! I just used an air compressor for the test. No blockages.

I may have a problem though.. while I was taking off the water pump base, the shift shaft as well as the shift cam came out with it. I’m unable to put it back in right now.

The driveshaft right now is in a position where if you turn the driveshaft in either direction it will spin the propeller in that direction. If turning the propeller clockwise while holding the driveshaft still the lower unit will click.

I couldn’t find anything on this.. I’m really hoping you know what’s going on?

Just want to thank you again for all your help you’ve been great!