here one opinion from ai
what would cause a 1978 2hp Evinrude to appear weak at wot if compression is ok
If your Evinrude 2 HP Outboard (1978) has
good compression but feels weak at wide-open throttle (WOT), the problem is usually
fuel, ignition, or prop/load related. These small engines are simple, so a few common things cause this.
1. Partially clogged carburetor (very common)
Even if the engine runs, a
partially plugged high-speed jet will make it weak at WOT.
Symptoms:
- Starts and idles fine
- Runs but lacks power at full throttle
- May surge slightly
What to check:
- Remove carb bowl
- Clean main jet and passages
- Blow through with carb cleaner and compressed air
Old fuel residue often causes this.
2. Ignition coil or weak spark
Older small outboards often develop
weak spark under load.
Possible issues:
- Cracked ignition coil
- Weak condenser
- Points slightly oxidized or mis-gapped
What to do:
- Check spark color (should be strong blue)
- Inspect points and set gap (~.020")
3. Wrong fuel mixture or stale fuel
That engine typically runs
50:1 fuel/oil.
Weak power can happen if:
- Gas is old
- Oil mix is too heavy
- Water in fuel
Try fresh fuel mix.
4. Exhaust restriction
Carbon buildup in the
exhaust port or muffler housing can choke power.
Signs:
- Engine revs but doesn't push the boat well
Decarbonizing sometimes helps.
5. Propeller issues
Check the prop.
Possible problems:
- Bent prop blades
- Fishing line wrapped behind prop
- Shear pin partially broken (very common)
A slipping shear pin can make the motor
rev but push weakly.
6. Fuel flow restriction
Check:
- Tank vent open
- Fuel filter screen in carb
- Fuel line blockage
A restricted supply limits
high-speed fuel demand.
Most common causes on those little 2hp Evinrudes:
- Dirty carb jet
- Weak spark (coil/points)
- Partially sheared prop pin
Quick test:
Run the engine at WOT and
slightly close the choke.
- If power improves → carb is lean / dirty jet.
- If nothing changes → ignition or prop issue.
