Exhaust "POP" on shut down.

[WCTori]

Hi guys, i've got a '93 Bayliner Jazz w/90hp Force/Merc Sportjet set up. Can anyone tell me what causes it to "pop" thru the exhaust when i shut it off.

It is one single, loud, pop. Doesn't matter if the engine has run for 5 seconds, or 30 minutes. Hot or cold. I've seen other outboards do this on shut down, and wonder why.

 

[jerryjerry05]

Timing?
Too much fuel in the system pinhole in the diaphragm?
Idle too high ?​

 

[WCTori]

This whole engine was recently at the shop and had the ignition upgrade. I assume timing is correct. It starts at a blip of the key, so i feel everything is correct. Would be good to verify i suppose. Anyone know the timing spec ? I haven't found an online service manual yet. I'll check to see if it'll idle down any further. I can see how that would make it do this, but im pretty sure all the throttle linkage has remained untouched.

Thanks for the suggestions.

 

[jerryjerry05]

Top of the Force Forum are posts that link to timing and synchronizing the carbs.
I worked with a guy who "​ Timed by ear"
I had to go fix his "fixes" when customers had trouble.
One motor was 30d off and started great but ran horrible.
Not saying yours is off but something to look into.
Do a compression test too.
What's the "upgrade"??

Assume, NOTHING ​

 

[WCTori]

I'll give the timing tutorial a look and check mine out. Mine not only starts well, but it runs perfect too. Thanks for the tip on the tutorial.

I believe it was the BOATS DOT NET site that listed "CDM CONV KIT (835084A1) COMPONENT PARTS" which i ignorantly mentioned at "upgrade" that is the commonly replaced RED STATOR, Harness, Flywheel,....etc.

 

[WCTori]

Alright, some insight to this strangeness.... Spent some time with this at the lake this weekend. It only does the pop if i turn it off with the switch. If i pull the lanyard, it does not pop on shut down. Any one know what the lanyard disconnects as opposed to what the switch turns off to shut the engine off ?

Checked the timing and it was reading at 0* @ idle. But then afterward i noticed my timing light was set on 10* (adjustable type) so i need to recheck it again with it dialed in at 0.

 

[Frank Acampora]

If it is NOT mercury ignition the lanyard (kill switch) and ignition switch are wired in parallel The both short the CD units capacitors to ground, preventing spark

 

[pnwboat]

Maybe give the ignition switch contacts a shot of contact cleaner, WD-40 or CRC. Like Frank says, there should be no difference between using the ignition switch or pulling the lanyard to stop the motor.

 

[WCTori]

Frank, any chance you have a wiring schematic you could share ?