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11-22-2017, 08:45 PM #16
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11-22-2017, 09:29 PM #175000 RPM
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Shift interrupter works as follows. It takes a fair amount of effort to make a big horsepower motor come out of gear. Both fwd and reverse. More so out of fwd because you're going WOT in fwd compared to reverse. . One reason for the extra effort is the "back-cut" of the dogs on the shifter/clutch dog and also on the matching dogs on the gears. And, the more hp, the more torque that is generated as the engine revs faster. That torque can be held gear against gear (dog against dog???) even when you come back off throttle. So, to minimize the effort to get those gears apart/break the torque. OMC decided to hesitate the ignition momentarily, as you shift the control box into neutrel. It happens coming out of fwd AND reverse. The shift interrupter mechanism is on the stb side of the shift linkage on the 'end" of the horizontal shaft at the fwd lower part of the block. It has 2 wires, blk=ground and blk/yellow= kill circuit to the power pack. This circuit is provided with a diode so that the ignition is only activated to the stb side ignition spark and not the port side. Some engines had two packs and only the stbd one was effected. As you shift out of gear, the switch rocks and grounds out the intrernals of the pack and hense, no spark to the three stbd coils. The engine continues to run but "stumbles' cause 3 of 6 cylinders are not firing. This happens fairly quickly and in no time you are in neutrel, the switch reverts back to "normal" position, the switch goes "open" and the engine now idles in neutrel back on all 6 cylinders. OMC had a fair amount of issues early on when they introduded this system but that was a few years earlier. Hopes this helps.
Last edited by King Dad; 11-22-2017 at 09:32 PM.
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11-22-2017, 09:36 PM #18Junior Member
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So basically, the design is to momentarily kill the engine?
If the interrupter switch is bad, what is the symptom?
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11-22-2017, 10:02 PM #19
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11-23-2017, 11:24 AM #20Junior Member
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05-14-2018, 07:08 PM #21Junior Member
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Hello,
I thought I'd come back and report what the issue finally appears to have been all along.
There is one screw on the spark lever. It wouldn't get a bite anymore in the plastic hole it sits in. This was causing the roller on the end of the spark lever to be about an inch away from the throttle cam after shifting back to neutral from foward. The roller needs to be just touching the throttle cam in neutral. But with that stripped screw, the spark lever could not be tightened to keep the roller where it needed to be. Hopefully this might help someone with stalling after shifting.
The 1-inch travel of the roller befoe touching the throttle cam was causing the engine to stall after shifting.
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05-15-2018, 01:40 AM #225000 RPM
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Another thing that I have found with those plastic carbs.
There is a plate on the starboard side held on with 5 screws.
This seems to be the idle circuit.
I have noticed on quite a few engines that you can get an air leak past the gasket.
I take the plate off on these engines and put a bit of a curve in the plate and re-assemble
This stops the air leak, which would make it run leaner at idle
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