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454XL, lacks power and won't rev past 2800 RPMs

May I ask what the purpose of doing the drop test is?
The spark plugs have been replaced (new)
The distributor has been replaced (new)
All spart plug wires have been replaced (new)
The ignition coil has been replaced (new)
 
May I ask what the purpose of doing the drop test is?
The spark plugs have been replaced (new)
The distributor has been replaced (new)
All spart plug wires have been replaced (new)
The ignition coil has been replaced (new)

Purpose of so-called "drop test" is to see if all cylinders are firing. This is more often done at idle, but could be done at any power setting.
Replacing all the ignition components doesn't guarantee all holes are making power.
You might consider yanking a wire out of the distributor, one at a time, and take the boat to WOT. Record each rpm. If the 8 rpm numbers are reasonably close, and a drop is noted from 2800, then we will all agree that all cylinders are actually firing and we can drop that thought.
I had to run a BB without 2 cylinders firing one time, for about 4 hours, across a 60 mile ocean passage. It was pretty smooth. btw, it was not suffering from an ignition problem either.
 
Hello
A little update,
I took the props out and double checked them. They are perfect, 19X17.5, 4 blade.
checked the stuffing boxes and are both good. I can turn the shaft with my hand with a little effort. that area is ruled out.
Not sure what else I can do. I am at a loss with this engine. I have taken 3 mechanics already and no luck.
It does the exact same thing.
Engine runs smooth at idle, no back fire, no strange noise, very smooth. The timing is right at 12 degrees and advanced to 30.
The boat throttles up to about 2500 RPMs and tops there, it does not bog down, miss, back fire or anything. It feels like a golf cart when it reaches the governed speed.
I have changed just about every system on this engine and the results are the same.
Any new ideas will be greatly appreciated
 
If you believe that you have exhausted all possibilities with regard to fuel and spark causes, then the next big rpm related issue would be valve train failure to perform at high rpm (valves not fully closing or not fully opening). The engine performance at low rpm and the compression check suggest that the valve train operates adequately at lower engine speeds. Possibilities that would cause high rpm breathing problems include incorrect (weak) valve springs, incorrect or failing (because of poor heat treat causing lobe wear) camshaft, camshaft timed to the crank incorrectly, and collapsing lifters (either failing or being supplied with foamed oil). Assuming your oil levels are correct, in a new long block all of these should be the responsibility of the supplier of the block. Maybe it's time for a phone call.
 
Have you verified clear exhaust path? no flappers laying anywhere? partially clogged elbow? collapsing hose or bad water muffler?
I had an issue on a IO single that drove me nuts...turned out the flapper rotted out of the y pipe and would intermittently partially block the exhaust. When this happened the boat seemed like it went into limp mode, wouldn't rev past 2-2500rpm. Just throwing out an idea in case you haven't looked. It's terrible what you're going through.
Good Luck!!
J
 
Thank you shock loaded
I did take the hoses off from the elbows back and stuck my hand in the muffler. I did not see anything out of the ordinary . all seemed OK.
I don't think I have any flappers in my mufflers. It is just a fiberglass wall inside. I will take it apart again and check the other side to see if there is any difference. I will also take apart the elbows and see if there is anything wrong there. I did do a vacuum test at around 2000RPMs at idle and the vacuum didn't drop, which would be indicative of a blockage, but I did that a long time ago and to be honest, I am not sure of the result so I ll probably not only run a vacuum test again, but will take apart the whole exhaust and visually inspect it.
I ll post the findings.
Thank you
 
Hello Makomark
The props are the originals that come with that Wellcraft 3300 Sportbridge
They are 19 X18 (mine according tho the propeller shop are 19x17.5) The transmissions are ZF63A, 1.5 to 1
 
Hello Makomark
The props are the originals that come with that Wellcraft 3300 Sportbridge
They are 19 X18 (mine according tho the propeller shop are 19x17.5) The transmissions are ZF63A, 1.5 to 1


That then means this should be a 33 to 35 kt boat when healthy.
 
When setting the static timing did you use a shunt plug which locks out any advance ? The presentation is exactly like insufficient spark advance although previous testing seems contrary. Might consider advancing the static timing a few degrees and see if there is any difference in top end performance. Any pinging orbackfire would require immediate back throttle and the assumption that insufficient timing advance is not the problem. The working theory is that something is wrong with timing and maybe the indicated timing is not correct. Just about out of guesses on this one. This caper is long overdue a success story. Hope you crack the code soon.
 
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Hello Makomark
The props are the originals that come with that Wellcraft 3300 Sportbridge
They are 19 X18 (mine according tho the propeller shop are 19x17.5) The transmissions are ZF63A, 1.5 to 1

That sounds like a 3 blade prop/gear ratio not 4 blade. My Sea Ray 390C runs 18X17 three blades with 1.5/1 ratio.
 
I had the same issue. I resolved the issue by installing a new gas filter in the inlet of the carburetor. When I removed the old filter, I couldn’t blow through it. It was almost totally clogged. Now I’m running 20 knots at 3200 RPMS which is the sweet spot for my 34’ Silverton Convertible.
 
I had a fuel pick up tube or straw that was kinda loose on the anti siphon valve. It would let fuel flow fine but if it wobbled just enough around the barbs on the fitting it would restrict the fuel flow. We pulled it off cut about 1/2 off the end and put it back on. That problem was solved and it was alittle frustrating to try and track that down. I have also in a rush put one of the little fuel filters at the carb in backwards and the motor ran almost exactly the way he mentioned uhck
 
Do everything you can to resolve fuel delivery issues first (check fuel pressure at the rail, both at idle and underway), empty your fuel water separator and/or change the filter, see if you have any other screens/obstructions, take off the anti-siphon valve and clean it out, blow through the gas tank vent to make sure that the vent isn't clogged.

If none of that helps start on ignition, but you have coil packs and computer control, correct?
 
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