1991 mercury 90hp 3 cylinder running rough

[Eoughphily]

I have a new to me boat I purchased with a 1991 mercury 90hp outboard. When I start it up, it seems to be misfiring/popping and will not idle. Once it gets below 1200 rpms it starts to shutdown. I cannot get it to idle long enough to put in gear when in the water or under load. Sometimes I can when I have the muffs hooked up. I can rev it up to higher rpms, but you can here the popping still just much faster. I started troubleshooting and have exhausted my knowledge of what is causing this. Below is a list of things I have done so far.

Serial number
0D028331

Current idler screw adjustment
Top - 1 1/4
Middle - 1 1/4
Bottom - 1 1/4

Seated idler adjustment screws and pulled out 1 1/2. Adjusted 1/8 at a time each way but there is no change in the misfire/popping.

Checked compression.
Top - 95
Middle - 95
Bottom - 100

Ignition coil resistance test
Top - posts .4 and wire to post 951
Middle - posts .5 and wire to post 917
Bottom - posts .3 and wire to posts 918

Attached in line spark tester on each plug and all are lighting up good.
Performed 1/4" spark gap test - has spark

Replaced fuel hose between inline filter and carburetor. There are no air bubbles. Fuel pump should be good.

Rebuilt carburetors, no gunk or anything found to be causing any problems.

Inspected read valves through inlet while carbs were off. Also examined carbs with air vents removed for any blow back. None seen, also air vents were clean.

Replaced spark plugs even though they looked ok.
Here is a video of it running.
Misfire?

Replaced inline fuel filter with a clear view glass filter.

Here is a link to a youtube video of it running.
https://youtu.be/-wqvtFeYtHs

At this point I am unsure if this is fuel or spark related. I havent done a cdi test with a dva adapter yet because I dont have one, it will be here on monday.

I did some further tests on the ignition system.* Below are the ohm readings I'm getting.

Trigger
Range is 800 - 1400
Wht/blk to brn 1216
Wht/blk to wht 1218
Wht/blk to vio 1220

Stator
Red to grd (low side)106 range is 75-90
Blue to grd (high side) 3780 range is 3250 to 3650

My readings are a little high out of range on the stator, could this be an issue? Any thoughts or ideas to help point me in the right direction would be so much appreciated. Thank you

 

[fastjeff]

That 1 1/4 turns is merely a starting point. Each carb needs to be adjusted correctly.

Jeff

 

[Eoughphily]

That 1 1/4 turns is merely a starting point. Each carb needs to be adjusted correctly.

Jeff

Thank you for your input Jeff. I agree, 1 1/4 turn is just a starting point. This is where it was when I bought it of which the owner claimed he just had it serviced.

Over the weekend I went through the entire fuel system again including a full carb adjustment. Any adjustments I make to the carb either makes it worse or doesnt make any improvements. I have also replaced fuel lines and filters with no change at all.

I have concluded the issue I am experiencing is related to the cdi ignition system. I have measured ohms and all look good there, but doesnt mean there still isn't a problem. I have a dva adapter arriving in the mail today to test the voltage. I'm hoping it isn't stator related, but if it is, im prepared to do everything it takes to get this baby purring.

If you have any experience in this area or any knowledge you can pass on I am all ears.