1996 90HP evinrude backfiring every so often

I have a 1996 90hp evinrude that has been running good for many trips out then it picked up a through exhaust backfire. The first trip I noticed a problem it was mid trip and it felt like it was missing and fiddling with it I found a lose plug wire and ran good back to the no wake zone and I noticed it again. Plug wire seemed good then heard a backfire. I checked spark and compression made sure everything looked tight and clean. Ran it again on the river and had no problems. Went for a ocean trip and had a few random backfirings.
I had a throttle adjustment that was not budging so I dropped it off with a local mechanic to look at both things. He took one side of the carbs off and said they looked real clean. It's a fairly new motor to me but it seemed well cared for. He put them back on and fixed the throttle problem and didn't get a back fire from it. I brought it back home and ran it before the next trip on muffs and it is still back firing. It has to warm up before it starts and it's random and at idle. I gave him a call, he said it's probably the power pack and he professed how much he didn't like this model for electrical issues. I replaced the power pack and it's back fires a little less frequently. I tried to consult him again and it seams he wants nothing to do with it. I replaced the coil packs as they looked a little cracked. I did skip the plug wires and I think maybe that lose wire and the backfiring have something to do with each other, and I should do the wires.
I've always heard that backfires through prop are electrical and through carbs are gas. Should I be looking at the carbs or dig deeper in the electrical?

Although I retired in 1991 and your engine design and circuitry may be foreign to me... many boaters confuse "Backfiring" with running "Lean" which is a common problem, hence my jumping in here.

If the engine is actually "Backfiring", that is actually backfiring like a shotgun blast out the exhaust... I'd be very surprised that it ran at all.... and there would be no mistaking that sound, especially when running on a flushette. Is this what you're encountering?

Or... is this more like a sudden hiccup, a sudden hesitation, a spitting back through a carburetor as you mention in not so many words within your last sentence? Regardless... do this quick test on your flushette as I've done countless times when working, as follows.

With the carburetor face plate(s) off.... the engine warmed up and at whatever rpm this problem is encountered (Not Over 1800 Though).... stick two fingers into the carburetor throat, acting as a manual choke, going from carburetor to carburetor.... when, if, the engine smooths out and the "backfiring" ceases, you've found a carburetor/cylinder that's running slightly lean.

Let us know the results of that test and we'll go from there.

There are 2 different 90 hp models in 96.----Post model # .-----Post compression values as well.

It is a E90ELEDR and the compression was 130 across them all.

The thing I am seeing is a noticeable puff out the prop, certainly not a bang. I have heard that bang out of an old 9.5 years ago. I may be chasing the wrong thing. The mechanic felt he resolved it after he was fussing with one set of the carbs. But it wasn't. I will run through those tests and get back to you with the results. Hopefully it will stop raining one of these days soon.
Thank you
Florida is tough this year with all the rain.

So I ran the carb test today. It takes a lot of time waiting between "sneezes", maybe 1-3 minutes between events. I started when I had heard three of them to be sure it was having the problem often enough. I ran the carbs through twice because the first time I got no sneezes. Second run through I heard sneezes on both lower carbs after about two minutes. When covering the bottom port side the rpms dropped to 800, others didn't change that much. The top port side one took a little longer, but after what seemed like many minutes the with fingers over it I did hear one. When testing the top starboard I just didn't get a sneeze. I am sure I waited many minutes listening for one. So I am thinking that this carb is my culprit.
With the fact that it can be minutes between sneezes I am thinking that I have some particle that is randomly moving around. Rebuild or just try to adjust. It has also gotten a little slow to start from a cold start recently.
One strange thing that happened while testing is each carb that I held my fingers over developed a puddle of white liquid in the mouth of the carb. I am thinking super aerated gas? One other thing is a few trips before ever having problems I added a water separator, the type with a clear bottom you can drain. I have checked it two times and found only a tiny speck of water one time.

The terminology you're using..... "When covering the bottom port side"... "with fingers over it"...

What exactly are you doing with your fingers?

I am speaking of actually sticking two (2) fingers directly into the carburetor throat. This in effect is changing the diameter of the venturi (hole through the carburetor), restricting the air flow and causing the fuel to flow into the intake manifold at a higher rate.

If there was anything wrong with the carburetors, it wouldn't come and go... it would be steady and you surely wouldn't have to wait the time period as you explained.

What you've had to say in your answers doesn't spell "carburetors" to me... With the engine having this problem, pump the fuel primer bulb constant and steady, acting as a manual fuel pump. Let us know what effect, if any, this has on the engine.

You mention in post #4..."Florida is tough this year with all the rain." Yeah, I know... just east of Tampa. And you are where?
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I had done the fuel pump check a couple weeks ago while trying to rule things out. No change.
It starts up a minute or two after the motor warms up and can be subtle or enough to stall it.
I had covered each carb with two fingers across the front not inserted.
So your not thinking carbs? I am going to bypass the water serparater with a spare tank to be sure there.
I am in Levy county near Bronson

Its not unusual for one to sneeze/backfire on muffs as these models(60 degree) needs backpressure on exhaust. As pop from exhaust is electrical/timing and a sneeze from carbs is fuel/carb related. These are known for bad plug wires also as wire burns off at spring terminal in boot...

I've taken it for a couple rides between repair attempts. Its been a confusing problem. After I replaced the power pack I took it to the river and a casual trip around with lots of idling had no problem. Took it out to fish in the gulf and had a few sneezes here and there during the trip.
Then replaced the coil packs since they were cracked a bit. No change. I know these older motors are not perfectly smooth idling but it didn't use to do this and it can be strong enough to stall it.
I am seeing it through the prop not the carbs.. plug wire connecters look good.

Change the optical eye