SoCal Jet Boats
Tech Talk => Engine Mechanical / Electrical => Topic started by: GArnold on May 29, 2023, 06:21:06 PM
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I have a 1998 Marine Power 454 and I launched the boat last weekend and after about 3 minutes idling, the engine sputters and kills itself. It would only start if I pumped/feather the gas pedal but would never remain idling. I put on a new Quadrajet and boat started right up and died again. If I manually held the choke closed the boat would idle fine. I started pumping the mechanical assembly that controls the secondary flaps and it started to idle on its own.
I was able to hit the gas and take off and seemed to only have about 60% throttle when I had the pedal fully pressed. It continued to run the same then grabbed and took off wide open throttle 100%. After about one minute, the engine bogged down and shut off. White smoke started billowing out the top of the carb and out of both valve cover breathers. Now there is a nasty metal/screech sound when I try and start it.
I am on my last leg with this boat because I have sank several thousands into complete rebuilt and still have issues. ANY help is appreciated.
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White smoke sounds like water getting into the cylinders ?. Do you have water in the oil?
And what do you mean completely rebuilt? Like motor totally gone thru?
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I checked the oil which only had less than 5 hours on it and it looked good. There has been two times the motor was pulled out and rebuilt. The first time was about 4 years ago and it got all new pistons and internal parts. Last year the exhaust flaps broke and water went through the exhaust and into the motor. The motor was pulled again and replaced the damaged parts.
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Are you running logs? What are the cam specs do you think it could be reversion? Does it do the same thing on the trailer running it dry
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Sounds like carburetor problems.
Start with the basics, a compression check.
If that is good, then it's sounds like carburetion.
Q-jets aren't your friend here. They belong on tow trucks and motorhomes. (In my honest opinion)
Tuning a q-jet can be done, but isn't as simple as a Holley.
Metering rods and and jets for a truck and usually too lean for a jet boat. The idle quality sounds like something is suspect. Q-jet should have a good idle, even on a jet boat.
Fuel pressure sounds like it's not steady at 7ish lbs to keep you running.
Non vented fuel tank(s) could cause this too, as well as a clogged fuel filter.
Several things you need to look into.
Make sure initial timing is good to go and your ignition system isn't failing either (bad coil or module?)
Dan'l
Just my $0.02.
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White smoke out of the carb sounds like you have too much fuel pressure and are overflowing the bowls but some of the other symptoms seem like its not getting enough fuel.
What is the fuel pressure to the carb?
I have a marine power 454 with quadrajet and the thing starts and idles like fuel injection.