Economy plummeting

Hi I have a 290 luhrs with 350 crusader tbi's and all of a sudden the fuel burn almost doubled. I did 70 miles and burned about 120gallons when it should have been 70 gallons. I cleaned the bottom and running gear, that's all fine. Engines seem to be running great. Except my port transmission, it has always spun in neutral sense I got the boat a year ago, but today it slipped a couple times when I floored it and I had to back off so it would catch and keep going. Fuel burn was bad on the last trip to with no transmission issue. Any ideas?


also I should be getting 300-400 more rpm out of wide open

I meant I did 50 miles and should burn 70 gallons but used 120

See if the flame arrestor needs cleaning. Seriously. Mine was dirty and it used a lot more fuel.

Jeff

I can give it a shot but burning 50 gallons extra is a lot

The gear slipping won't help but sounds like that isn't the primary contributor....when was the last tune up done? FWIW, ignition cables have a finite lifetime, especially on a boat, and intermittent loss of spark can do just what you described.....and you need a really keen ear to even hear it. any floscan or equivalent in use? just wondering if it is both engines vs one....

makomark said:

The gear slipping won't help but sounds like that isn't the primary contributor....when was the last tune up done? FWIW, ignition cables have a finite lifetime, especially on a boat, and intermittent loss of spark can do just what you described.....and you need a really keen ear to even hear it. any floscan or equivalent in use? just wondering if it is both engines vs one....

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Plugs were done lastyear and I'm not sure about the wires. And no there is not a flowscan
also what is fwiw, not sure if I've heard that before

I know you said bottom cleaned, but R the props really cleaned of all hard stuff? WOT is a good test of overall condition, and down 400 says something is wrong with the boat hull, and maybe both engines. You say "should get 400 more"; does that mean "it used to get 400 more"? sorry for all the semantics, but i'm a long ways away here. Also, one more time: check plugs, for nothing else than a rich plug set or a single bad wire. This might instantly lead U to the problem engine. You need a port clutch pack, but you already know that. Of course, slipping at speed is big time heat going out the ATF cooler, and that kills economy. Per MM point, I crossed the gulf stream once with a single V8, that had two totally inop. cylinders. The wife, onboard, never knew; it was still pretty smooth.

Yes I lost 1000 hp so I cleaned the bottom and running gear and now I'm loosing 400, I talked to a mechanic and he said if the tranny slips it revs up. But it didn't it was revving down, so now I'm starting to think its fuel or spark

and yes thanks I do need a clutch kit

IF that tranny was slipping that bad, it would have fried itself within minutes.

Jeff

check the spark advance too....