'94 Johnson 48hp SPL Bogging under throttle

[Arete]

I've been trying to fix a buddies '94 Johnson 48hp with zero luck. Problem: Under about 3/4 throttle the engine will bog down and come close to dying. It feels like fuel cut in a car. Once it happens, you then have to return to idle for a few minutes before you try to add throttle again or it will continue to bog at any throttle level. I've searched many threads and have seen this is a common problem. With that in hand, this is what I've done:

Fresh fuel; fuel tank are clean; tank pick up is clean; tank vent is clean; line from tank to quick disconnect is new along with a new primer bulb; quick disconnect is clean; fuel line from quick disconnect to fuel pump is new; fuel pump and fuel filter are new; fuel line from fuel filter to manifold is new; manifold is clean; fuel line from manifold to carbs is new; fuel line from manifold to primer solenoid is new; primer solenoid was rebuilt; fuel lines from primer solenoid to carbs are new; both carbs were rebuilt and checked (floats fine; needles fine); intake gasket replaced; carb gaskets replaced.

I've checked for any air or fuel leaks and things look fine. Under throttle I've tried to use the primer when the engine bogs with no luck. I've also tried to force fuel via the primer bulb with no luck.

The engine idles great in the driveway on the trailer, and even revs fine in the driveway as well. I thought this was a good sign but... When in the water the idle is fine, however, as soon as you start to give it throttle it bogs. Now even sooner then before all the things I did. Like at 3/8 throttle now.

Is there something I may have missed? I've checked fuel and air. All I have left is spark. Any ideas or things to check would be appreciated.

Really trying to fish this weekend...

 

[tx1961whaler]

Re: '94 Johnson 48hp SPL Bogging under throttle

The next thing to do is check the spark with a spark tester.

 

[Arete]

Re: '94 Johnson 48hp SPL Bogging under throttle

I had a buddy who does small engine repair (lawnmowers) bring a spark tester and compression tester over.
The spark tester showed what he said was a good spark on both cylinders. It was a purple and orange colored spark. His tester was the kind that uses an inline bulb.
The spark plugs were checked and looked fine. Gaps were properly set at 0.030".
An engine compression check showed 140 and 135 respectively. My buddy said that is good compression for a small engine.

We talked about what could be the problem. Is it possible that this could be an intermitten problem related to load. Example: Coil works fine at idle but cuts out when under load. Is there a way to check for this?
I read somewhere in my searching about a piece of the propeller shaft assembly wearing out and the prop not spinning under load causing a stumble. Anyone heard of this? Any more ideas of what to try and troubleshoot.