1984 Evinrude 70hp

[Mfisher0918]

I am at my wits end and hoping someone can help. I have a 1984 Evinrude 70hp on a 20ft pontoon boat. It idles fine but falls flat on acceleration. (Only in the water under load). I can "feather" the butterflies and get it to "catch" and then I can take it to full throttle and it runs like a champ. I can also engage the electronic primer to get to full throttle. This motor came off of a 14ft V-hull and runs perfectly on muffs.

Here is what I have done so far:

Rebuilt carbs, also took them back apart twice to double check and make sure everything is clean - it is. These carbs have fixed orifices so no jet adjustment

New plugs/wires

Checked resistance on all three coil packs - Good

All new fuel lines/primer

Rebuilt fuel pump - I believe it is working because pumping the primer bulb during attempted acceleration does nothing

Compression check - 125ish on all three cylinders

Spark test - good spark

Timed and synced per manual with timing light

I have no idea where to go from here. I have spoken to a talented Yamaha mechanic and he also has no answer.

Please help!?

 

[w2much]

compression check ? fuel delivery from tank. check for air leaks . spray some wd or starter fluid around the manifold.check your hoses are not deceiving you with cracks or holes. be certain of your plug gap.Let us kknow how you make out.

 

[Mfisher0918]

I have been through most of that. new plugs (gap set), all new lines with new clamps. Haven't tried spraying starting fluid around the intake