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496 ho questions?

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Old 01-20-2009, 05:09 PM
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Default 496 ho questions?

1st thing....I'm new to the whole big block thing being that I've been into drag outboards for so long but am willing to learn and somewhat mechanically inclined.....Just haven't done a whole lot on car motors!

#1. Boat has been sitting for around a year now and has around 8 gals. of old gas in it. I put 10 gals of 93 oct. in with some booster and fired it up and started missing a lil on one side. Should I drain all fuel and start fresh?or just add some seafoam and fuel injection cleaner and run all the fuel out?

#2. Before she sat for a year I was having some water pressure issues and the buzzer was going off. Kinda wierd b/c It would be normal on a run then you stop, fire it up again and the pressure would be low....Would'nt it be a steady lower pressure for a water pump problem? Sounds to me kinda like a floating blockage somewhere? Where do I start looking? Heat exchanger?


Thanks ahead guys....
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Old 01-21-2009, 08:53 AM
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Drain all the old fuel and start with fresh 87 octane.

Impellers are cheap for the 496. Remove the old one...it may be missing some vanes and on the way out. Backflush the system to ensure you do not have pieces of old impeller floating around somewhere.
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Old 01-21-2009, 09:24 AM
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K4Me is right on the mark... Flush/Impeller/Clean Fuel/Injector Cleaner.. in that order.
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Old 01-21-2009, 10:26 AM
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The heat exchanger does tend to catch pebbles so along with the new impeller (which will likely need a new housing as well) I'd pull the exchange apart as well as it's a 10min job at most.
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Old 01-21-2009, 10:55 AM
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Make sure you relieve the pressure on the heat exchanger if you haven't done it and before you replace any parts for water pressure. They could have been pumped out and need to have the air pressure relieved by pulling the release valve above and on the right side of each heat exchange cylinder.

If that doesn't do it then follow the good advice above and you should be ok. Also, if the gas replacement doesn't do it you may need to clean or replace the injectors but that's not that big of a deal (I hear).
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Old 01-21-2009, 05:30 PM
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Thanks guys!, Will drain the fuel today and get started.....How do you backflush the raw water cooling system?
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