Dan has been dealing with some pretty heavy issues lately….Please forgive him….
While Dan is truly the go to guy on these engines, there are others of us here that can help out I’m sure….
OK, did my best to read all yours/Dan’s posts on that website…
So, you premix, correct?
Let’s back up a bit and talk about the history of this engine/rig. When was the last time it idled/accelerated OK? How long was it between the last time it idled/accelerated OK and the next time you used it when it didn’t run OK?
I understand you use the rig at altitude sometimes, which would probably have the effect of making the engine idle a bit richer. And, like Dan says, the idle air bleeds are handled in just the opposite manner as conventional fuel jets, which gets confusing…But, I am assuming you have not changed any air bleed sizes, just performed the old toothpick trick. Dan’s information concerning trim position is spot on, but you are correct also. Trying to accelerate when trimmed out will result in poor acceleration and ventilation (prop loses its bite on the water and slips, causing the engine to rev up but boat speed does not increase)…Sounds like you experienced propeller ventilation, not an engine problem, when you accelerated while trimmed up a bit. Generally, it is best to trim out a bit while idling around the harbor, but then you will have to trim down again before accelerating.
When the engine idles poorly, is it sneezing/coughing when it stalls? If so, that is generally an indication of a lean condition. Resolving the idle condition will probably repair the off idle/acceleration problem.
Is this engine developing full power? What RPM does the engine turn up when properly trimmed at WOT? Do you know the style/pitch size of the propeller? An engine that isn’t developing full power is not going to accelerate/idle properly. When was the last time this engine has a compression test? Perhaps the engine is not running on all six cylinders for one reason or another.
Sounds like you have had the carburetors apart a few times. But, there is a synchronization procedure that must be right or the engine will never idle/accelerate properly. All the new carburetors/jet changes will not compensate for a carb that is not closing fully at idle, cam pick that is off, or ignition pick up timing that is wrong.
These engine also have an ugly issue where the timing magnet sensor ring comes loose under the flywheel, which can cause erratic/no idle conditions, the flywheel key could be sheared as well, this will have the same negative effects. Flywheel key condition can be checked using the TDC tool to check flywheel location. Yes, you could remove the flywheel to check the key, but this is near impossible without the proper tools. A loose flywheel timing magnet will show up on a timing light, a sheared flywheel key will not.
So, I’m thinking we need to back up a bit, you have had the carbs apart a few times. Dan spoke of the top gaskets getting crushed causing a fuel restriction, it’s amazing how they look like "they were made that way" when you inspect them. If the gaskets are tan in color, they are the newer design that is not prone to this problem.
If it were mine, I would start with the compression test. From there, I would take the time to synchronize the engine properly, using the TDC tool to check flywheel positioning on the crank. Like Dan says, the engine will idle poorly if it does not get up to temperature. I’m not sure if this engine has the quikstart feature, which messed with idle timing to help the engine warm up. If so, this could be an issue.
The other thing I thought of is a leaky electric primer, which would cause a rich condition at low speeds, but not effect WOT performance that much. But, if the engine sneezes/coughs/spits, this is an indication of a lean condition, which more or less rules out a leaky primer…..