I have a 1996 evinrude 35 hp that has not been run in 3 years it trys to start some but i have intermitted spark to the plugs and if it does run it is only 1 cylinder

Based on the information provided, it seems like you have already checked and replaced some common components that could cause the described issue. However, there could be several other potential causes for the problem you're experiencing with your Evinrude E-TEC outboard motor.
Here are a few additional suggestions to consider:
1. Ignition System: Check the ignition coils, ignition timing, and spark plug wires for any signs of damage or malfunction. Ensure that the spark plugs are properly gapped and the correct type for your engine.
2. Carburetor or Fuel Injectors: If your outboard motor has a carburetor, it may be clogged or in need of adjustment. Cleaning the carburetor or checking the fuel injectors for proper operation could help resolve the issue.
3. Air Intake System: Inspect the air filter and intake manifold for any obstructions or blockages that may restrict airflow to the engine. Make sure the air filter is clean and functioning correctly.
4. Compression: Low compression in one or more cylinders can cause poor starting and running issues. Consider performing a compression test to determine if there are any abnormalities in the engine's compression.
5. Electrical System: Check the battery voltage and connections to ensure they are in good condition. Faulty electrical connections or a weak battery can affect the starting and running of the engine.
If you have performed all these checks and are still unable to diagnose the issue, it may be best to consult a certified marine mechanic or an authorized Evinrude service center. They will have the expertise and specialized equipment to diagnose and resolve the problem with your outboard motor.

OK, spark plugs wet. We both know that means flooding. Try a start with ether. Then if it fires, it's either fuel pump or carbs.

evinrude 1978 -1979 have a capacity discharge ignition unit as the control for the spark system
it runs wires to an ignition coil
so I would be suspicious of that unit
check all connections for corrosion and bad connections
I typed in electrical schematics for 1978 evinrude out board engine and found a site --www.maxrules.com which in the list of schematics has 55hp 1977-1978
press on that and you get a schematics of the wiring diagram evinrude 1978-1979 55hp
now I am aware that you state that yours is 35 hp but if it has 2 cylinders then it is a fair bet that the wiring diagram will be the same
any way there are plenty of other sites that may be of benefit

The float in the carburetor has sunk or the fuel inlet valve is leaking letting in too much fuel.

1978 It is in the model on an Evinrude. 6804.... 6 HP.....1978

Checked the vent cap on the fuel tank?
Check if it runs again great after pumping fuel...
Check when it drops power if both spark plugs still sparks...
You can have a bad coil or cdi...

any colour differance with both spark plugs

carb is CV type with diapharm may be deterioated, gummed up from cleaners

or water in the carb bowls drain them

other is ignition issues or bad plug

FIRST CHANE THE PLUGS DONT CLEAN CHANGE

Hello enjoy42. From the information you have provided I would lean to the weak cylinder coil. Unplug the good spark plug wire & test run the engine on the weak cylinder. You could go to swapping the coils on the cylinders. Check your wiring terminals on the coils. Check with a marine dealer for the correct plug. I owned a 35 Evinrude on a Bass boat & it would out run my buddys 40 Mercury. Good Fishing.