454 NO POWER

HI I have a merc454 carburated

HI I have a merc454 carburated W/ thunderbolt igniton when i when i frist leave the dock i will bring it up to 3300 rpms and she runs like a top but when i bring the engine back down to an idle and try to go fast again the engine has no power but it seems to be running on all cylinder at idle but no power in nutural or drive BUT if i shut the engine down for like 10 or 15 minutes and start it back up it will go to 3300 no problem but when i slow down it does the same thing

"Well,what type of boat is it

"Well,what type of boat is it in,is 3300 your max rpm wide open? You could be in need of a carburetor rebuild. There is not much to go by from what you said. When was the last time the engine was serviced? It could just need a good tune-up.
Sorry can't be of more help."

3300 is not my max thats what

3300 is not my max thats what i always run at it had a full tune up 4 years ago and carb was rebulit 2 years ago

"4 years since it was tuned? I

"4 years since it was tuned? I think that would be a good starting point. What do you think? Sounds like the boat needs a complete service. When was the last time these services were done?Oil changed both engine and outdrive. Water pump output checked, U joints + all fittings on outdrive greased.inspection of bellows,shift cable,gimble bearing,sea pump checked if it has one. Condition of power steering oil. Trim oil and all hoses on all systems. Thermostat replaced when? Engine alignment to outdrive last checked. Engine compression was last checked when? Were the plug wires and cap,rotor replaced with last tune-up? Now with a tune-up thats about 5 or 600 bucks worth of work easy. The problem should show up in there at some point. Good luck."

the boat is stright inboard an

the boat is stright inboard and i am a machanic myself and i keep the engines is very good tune the oil is changed often and the cap rotor look good i have never had trouble with these engines till now and i cant figure out this problem

I can think of only 3 things 1

I can think of only 3 things 1. Clogged fuel filter 2.Fuel tank vent is plugged 3. Ignition Amplifier. ON the outside chance (It happen to a boat I was working on). The person was using a fuel additive. That silver cover on the bottle must have come off and went into the tank. if you kept the tank half full the boat ran great as soon as it fell below 1/2 the engine ran crummy what was happening the top that fell in the tank
was getting caoght on the fuel pick-up tube and resriction the fuel.

"It would have saved me a lot

"It would have saved me a lot of time if you had said that it was a inboard in the first place when I asked what type of boat it was in. What model / brand carburetor is on it? If Holly may have power valve / metering plate problem. Q-jet, sticking metering rods, secondary valves sticking? Vacuum check? Is it worse with more throttle? Does it come out of it with WOT? Is it running too lean / rich?
Is this only when you back off and power back up? If you do not slow down,does it stay running the same or does it loose power on it's own with no throttle change?"

"Being a mechanic, I guess you

"Being a mechanic, I guess you checked all the basics. Could it be a bad ground or connection going to the ignition module? When it is running bad, work the trim tabs or some other high amp electrics. Does it get worse? That happened on my Searay and it turns out I had a bad ground. Good luck."

when i am running at 3300 i ca

when i am running at 3300 i can give it more with no promblem and it will run all day at that speed but when shes brought down to an idle it will have no power but it will idle all day at 640rpms all day

Maybe the thunderbolt ignition

Maybe the thunderbolt ignition isn't giving any advance during that intermediate stage. Have a timing light ready when it happens again. The only other thing I can think of is some crap on the bottom of the float bowl.