1985 9.9 evinrude misfire

[Tiki91]

1985 9.9 evinrude 9.9 has misfire on lower cylinder has 110 compression on both. Cly getting spark on both as well as fuel.have swapped out coil,power pack stator and trigger within spec and no sigh of water intrusion.but is a excessive amount of unburnt fuel out the prop exhaust it will pop occasionally.did a drop test and stayed running on top cly but only for a few seconds on lower cylinder.any thoughts?

 

[racerone]

Checked fuel pump diaphragm? -----Cheap and easy to replace diaphragm if it is ruptured.

 

[cyclops222]

What ratio of oil to gasoline ? What brand of oil ? What is the oil rating for. ? 2 or 4 stroke rated ? Is there a white cream cheese glop on the lower unit ? When did this start ? change of oil or gasoline or sparkplugs ? What does the sparkplugs look like ? Can yo post a clear picture of the ends ?

 

[cyclops222]

What ratio of oil to gasoline ? What brand of oil ? What is the oil rating for. ? 2 or 4 stroke rated ? Is there a white cream cheese glop on the lower unit ? When did this start ? change of oil or gasoline or sparkplugs ? What does the sparkplugs look like ? Can you post a clear picture of the ends ?

 

[cyclops222]

What ratio of oil to gasoline ? What brand of oil ? What is the oil rating for. ? 2 or 4 stroke rated ? Is there a white cream cheese glop on the lower unit ? When did this start ? change of oil or gasoline or sparkplugs ? What do the sparkplugs look like ? Can you post a clear picture of the ends ?

 

[saltchuckmatt]

Describe how you tested the spark on your plugs?

These parts you swapped, brand new OEM parts?

 

[Tiki91]

Describe how you tested the spark on your plugs?

These parts you swapped, brand new OEM parts?

Spark tester . parts came off a good running motor.i have done dozens of these motors but this one has me baffled.

 

[Crosbyman]

did you replace/swap plug wires themselves.

what resistance do you see plug boots to engine frame ground . do you see steady resistance value if you flex the wires while measuring

 

[saltchuckmatt]

You need a spark JUMP tester. Nice, bright blue 3/8 jump.

Post two, fuel pump.
Have you pump the primer ball to see if it helps?

Does gas spray on your hand if you put your hand up close to the carb?

 

[cyclops222]

Being very lucky with used parts ? All gone.

 

[Tiki91]

did you replace/swap plug wires themselves.

what resistance do you see plug boots to engine frame ground . do you see steady resistance value if you flex the wires while measuring

Yes and yes

 

[Tiki91]

You need a spark JUMP tester. Nice, bright blue 3/8 jump.

Post two, fuel pump.
Have you pump the primer ball to see if it helps?

Does gas spray on your hand if you put your hand up close to the carb?

Reed valves are good engine starts very easily

 

[Tiki91]

Reed valves are good engine starts very easily

Primer ball pump no difference

 

[Tiki91]

did you replace/swap plug wires themselves.

what resistance do you see plug boots to engine frame ground . do you see steady resistance value if you flex the wires while measuring

 

[tphoyt]

Sounds like a silly question but have you tried new plugs? I once had a cracked plug that would randomly cause a miss fire. I found it by accident while running in the dark. It would occasionally ark to the head.
And how about that fuel pump diaphragm?

 

[saltchuckmatt]

Timing light out on the boat, gray or dark sky's and see if your loosing spark or the flash in this case.

Sounds spark related. Have you pulled the flywheel?

 

[Tiki91]

Sounds like a silly question but have you tried new plugs? I once had a cracked plug that would randomly cause a miss fire. I found it by accident while running in the dark. It would occasionally ark to the head.
And how about that fuel pump diaphragm?

3 different sets all the same results .new fuel pump also no difference

 

[tphoyt]

Crazy one you got there.
Matts plan with running with a timing light will at least confirm or deny a spark loss. It worth a try. Best of luck

 

[kbait]

Reed valves are good engine starts very easily

Did you pull intake manifold to check reeds? One leaf broken/blocked open will cause your issue and still start easily. Powerhead removal required, unless you can get to that bottom intake mounting bolt..
Leaky upper or lower crank seals could also cause issue, but rare on those motors.