2001 2 stroke v60 150 backfire??

[Jquest]

I haven't been able to get out in like 2 months. I usually start my engine once a week. Last two times...I've had a single back fire on the initial start. I let her warm up and shut her down. On the warm up she revs down(900rpm) as the temp comes up. She reaches normal operating temp and stays there. On the restart she doesn't do it. I replaced the pulse limiter two years ago. I've done the timing with the OMC module that connects to the engine. I know if I let this persist...I can blow the reeds. Any pointers would be gladly appreciated.

 

[HighTrim]

Re: 2001 2 stroke v60 150 backfire??

Backfiring out of the exhaust port is caused by having the ignition system fire a particular cylinder when the exhaust port is open ( ie piston down). This would sound like a shotgun going off..... is this the condition that you're experiencing?

This is usually due to a sheared flywheel key, a flywheel with melted (moved) center sensor magnets if they exist, timer base leads routed incorrectly to the powerpack, or having the leads from the powerpack to the coils reversed to mention a few.

Spitting back, sounding like a mild backfire, indicates a carb slow speed restricted jet..... something causing a lean carburetor scenario.

Remove the carb face plate and with the engine running and with that coughing condition existing, stick two fingers into the carb throats, one carb throat at a time. This action will be a manual choke of sorts.

If you find a problem carb, the RPMS should increase a bit and the coughing should stop. This would reveal an idle air bleed jet that has a slightly too large ID.

If you can't find anything wrong with the fuel system, consider a possible leaky lower crankshaft seal, admitting air to the lower cylinder and resulting in a lean sneeze.