1984 Evinrude 8hp pulsates at WOT. Puzzled by this one

[Doubledame]

Take a look at the video and you'll see the pulsating issue I'm talking about. I've worked on tons of these and I've been messing with this one for a bit and it's driving me nuts. Curious if anyone knows what might be causing this. When I pull the hood off it improved and it doesn't pulsate as bad and can get it up to higher RPM before the pulsating kicks in. I did some research on this and found some suggestion that it could be the exhaust housing gasket. Before I go that far I thought I'd check with forum folks.

I've pulled and gone through all the basics...pulled the carb & cleaned meticulously multiple times, excellent compression, spark is great, good gas.

Thank you if you can help!!
DJN

 

[jimmbo]

Might be an exhaust leak, But it might be an intermittent loss of spark. Examine all wiring pertaining to the ignition system. Observe the throttle linkages as you accelerate the engine to see if any wires are being pinched. Loose connections. What condition are the spark plugs in? You say the spark is "Great". Is it jumping a 3/8" gap?

 

[Bosunsmate]

look at your two plugs, any difference?
Maybe its the bottom seal (thats a wildcard)

 

[flyingscott]

What does it do on the lake in gear? A miss in neutral while overreving does not mean a thing. And your tub does not have enough water.

 

[jimmbo]

It must have been deep enough to prime the pump, as it is pumping water.

 

[Doubledame]

So a couple things...spark does jump a 3/8" gap. No difference between running in tank and on the lake. In fact, it bogs out a little quicker under load. Plugs were replaced early on the diagnosis process and look the same after inspection and running it. I've gone through the wiring as suggested in the post. I'm wising it was something and most times it is. I haven't looked under the flywheel yet, but I'll keep checking things off the list. Thanks for messages so far.

 

[flyingscott]

Have the fuel pump and/or carb been serviced lately? Tried a different tank?

 

[jimmbo]

Do you have a video of it doing that with the cowl off, taken on the Port side?

 

[Doubledame]

Have the fuel pump and/or carb been serviced lately? Tried a different tank?

Yes, both have....the pulsating happens immediately so I'm doubting anything with the fuel pump

 

[racerone]

Run with timing light and observe what spark is doing.----Test both cylinders.-----Use a strong fan to blow the exhaust away from your test tank.------Check flywheel key.-----Check for throttle plate opening too early.

 

[Doubledame]

Run with timing light and observe what spark is doing.----Test both cylinders.-----Use a strong fan to blow the exhaust away from your test tank.------Check flywheel key.-----Check for throttle plate opening too early.

I'll check on the cylinders with a timing light....others I've done/checked. Thanks!