I have a 1983 35 hp Evinrude 2 stroke. It’s running ok. I cleaned and rebuilt the carb. New plugs, new impeller, serviced lower unit….basically got it ready for the season. Compression is good 100 on both cylinders.
What’s making me crazy is, when it’s idling cold it misses about every 30 to 60 seconds and blows a puff of smoke from the exhaust port. When it’s warmed up the missing lessens to about every couple minutes it’ll miss without the smoke.
On the water it runs fine but still gets a hiccup every now and then. Any hints on how to clean that up?

Could be a bad spark plug wire, loose connection, coil or weak power pack. I had 35HP Johnson and it was a great engine many years of service running the marsh eventually I went to a larger boat and a 40HP Mercury. The only issue I ever experienced with the 35 HP Johnson was the power pack failed but it was cheap and very easy to replace. Went to the local dealer bought a new PP and was on the water the next day.

Possible lean sneeze? If it has one on the carb, might try turning the idle/air mix screw out I believe it is, just a tad. Maybe a 1/4 turn.

It's a rich cough, your just a little to rich on the idle circuit. When she warms up you said it lessens and no smoke which is the engine is burning the idle mixture better when it gets to temp.

Now, you make certain you have the correct Champion plugs, these motors were built to run the Champion plugs not NGK. You got that and gapped right, you need just ever so small amount of the idle fuel mix pulled out of her. These motors will have trouble running on fuel with any amount of ethanol, best to use alcohol free fuel, as that can make them cough like you mentioned also. So make your fuel right before doing any adjustments on carbs.

My boat motor runs better on non ethanol gas

I have a 40 HP mercury 2 stroke 4 cyl. I had so many issues with this engine coils,hard starting, powerpack etc. smoked like crazy until hot. Well, found out a past owner installed the wrong spark plug. This engine uses a surface discharge spark plug "no gap to adjust" Plugs installed were a gap of .071. The plugs I needed had a gap of .016...
Runs great now.
Rule of thumb is check everything. When you assume well you know...

Lots of the older Mercury's were built to use the surface gap plugs. I prefer them when you can run them too. There are several advantages to using them, when ran on the right engine and the right environment. NGK builds some really hard to beat ground electrode gapped plugs though.