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Not Firing

R

rollercoaster

Contributing Member
"Back again, 40 hp Mercury 4 c

"Back again, 40 hp Mercury 4 cyl. not firing all cyl. Checked trigger wires DVA adapter, black to brown 6.1 volts, pink to white 6.7 volts. Checked stator red to red/white 39.2 volts, blue to blue white 3.6 volts. Test done with wires disconnected for trigger & stator. Tried connected for stator, 39 volts red to red/white, 17 volts blue to blue/white. still need help.
Would like to send photo of engine. How do you reduce size below 100kb?"
 
"Clarence,

You can use any

"Clarence,

You can use any photo editing program or we have a very basic resizing page on this site here.

I have posted your photo below.

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Lets find out what cyl isn&#39

Lets find out what cyl isn't firing with a timing light on each plug wire. Or due you mean the engine is not putting out much power? Check compression and then clean carbs if spark check is ok.
 
"Checked all cyl. with timing

"Checked all cyl. with timing light, non are firing. Tried removing black and yellow wire from switchbox, no fire. Trigger put out over 6 volts, black to brown and pink to white. What next?"
 
"I am thinking switchbox. Exac

"I am thinking switchbox. Exactly how does the switchbox work? Ther is voltage from the trigger to it, but non to coils. Is there a way to check switchbox?
Thanks!"
 
"Switchbox is kinda like the b

"Switchbox is kinda like the brain of the ignition system.

Stator produces AC power that is used for both the ignition and charging the battery depending on which bobbins are supplying the power.

The trigger produces an AC pulse to tell the cylinders which order to fire in.

The switchbox takes the ignition AC from the stator, converts it to DC (rectifies it) and stores it in a capacitor (one capacitor for each cylinder).

The switchbox also has an SCR switch in it (kinda electronic distributor). The SCR reads the pulse from the trigger and then releases the energy stored in the capacitor for the appropriate cylinder.

Other components of the switchbox include a couple circuits, blocking diodes and various other "stuff" (not the technical term)


That energy (which is usually between maybe 200-400 volts DC) is sent to the appropriate coil which up converts it to 45,000-55,000 volts to fire the spark plug.

There are no serviceable parts in the switchbox and if any of it's components get toasted, the entire unit must be replaced.

And as JB notes, it's easiest to test all the other components (stator, trigger, coils, wires and plugs) - all of which, save the plugs, can be tested with an ohm meter at least initially."
 
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