Mercury 115 2+2 Backfire

[Cweaver]

My 96 Mercury 115 is backfiring through the carbs around 2000 RPM either when throttling up and coming down. Runs perfect at idle and once you get it above 2500 just spits 3 or 4 times at around 2000 rpm then goes to normal. I just changed switchbox and trigger a few months back to fix another problem then this started. Looking for any suggestions. Thinking it could be in the accelerator pump when cylinders 3 or 4 come online since it is around that 2000 rpm range. Since it runs fine at idle and high rpm I don't think timing is an issue. Really appreciate any input

[nitro_rat]

Maybe yank the air box and run it to see for sure what cylinders are having a problem and go from there...

[Dave Strong]

You changed the trigger, did you do a complete link and sync after. These motors need it done exactly right or they will run poorly. Why did you originally replace switch box and trigger?

Dave

[Cweaver]

replaced switchbox because the kill circuit was shorting out internally after motor warmed up only reason I replace trigger was because it was the only electrical component on the engine that has not been replaced recently. I have not done the link and sync procedure, it runs so good at idle and cruise I didn't think I would need to.

[Dave Strong]

Must do a complete link and sync after replacing trigger.

Dave

[Capt.Insane-o]

The past couple years I've replaced a few accelerator pump diaphragms. They are starting to get stiff and the nylon plunger we're swollen and sticking in the bores.