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85 Barefoot

carb question/problem?

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85 Barefoot

1997 ski nautique with 351 (carb).  I bought it last summer and have put 50 hours on it in the last 10 months.  Requires some throttle pumping to start and a few minutes at high idle but otherwise, its run well.  1000 hours. 

This weekend when I was skiing (and driving, not at the same time), upon significant throttle application, the engine either died, or significantly cut out unless throttle was reduced.   Did it 6 times.  So, to pull up a skier it requires very light throttle application to get up to speed.  Gas is good and fresh.  The times it did not die it would sound like a cross between an aluminum can crunching and a P-51 at startup, one time, and then stumble and accelerate.  Was that a "real" backfire?  Thoughts as to problem and remedy?  Thanks.

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85 Barefoot
5 hours ago, 85 Barefoot said:

1997 ski nautique with 351 (carb).  I bought it last summer and have put 50 hours on it in the last 10 months.  Requires some throttle pumping to start and a few minutes at high idle but otherwise, its run well.  1000 hours. 

This weekend when I was skiing (and driving, not at the same time), upon significant throttle application, the engine either died, or significantly cut out unless throttle was reduced.   Did it 6 times.  So, to pull up a skier it requires very light throttle application to get up to speed.  Gas is good and fresh.  The times it did not die it would sound like a cross between an aluminum can crunching and a P-51 at startup, one time, and then stumble and accelerate.  Was that a "real" backfire?  Thoughts as to problem and remedy?  Thanks.

@Woodski

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csleaver

A low float level or problem with the accelerator pump circuit in the carb may cause that kind of running issue.  Low fuel flow to the carb caused by a faulty anti siphon valve, tank pickup tube, fuel supply line, fuel tank vent, inline filter or fuel pump could also cause it.  Or maybe even a combination of any of those things.

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85 Barefoot

wow...thanks, I think!  Whats next step?  A REAL mechanic to look at?

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MadMan

It sounds like the carb is running out of fuel.  The most common reason for this is the fuel pump.  I'd throw one on it.

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csleaver

I would run the boat on a small portable fuel tank, like outboard motors use, and connect it directly to the fuel pump. 

If the boat runs ok on the portable tank, the problem is with one of the fuel tank components, supply hose or filter.  Start with the easiest parts (fuel filter, supply hose) and work your way to the more difficult ones (tank pickup, anti siphon and vent hose/fittings).  

If it has the same running issues using the portable tank, then the problem is on the motor (check the fuel pump pressure, rebuild and adjust the carb, so on so forth).  After the boat runs right on the portable tank, hook the boat fuel system back up and see if it still runs properly (there may or may not be multiple issues causing the running problem).

Whenever there are running issues that seems like a fuel problem, I recommend an engine compression test first to make sure the motor can perform when the fuel and ignition system are also working properly.  It is also an ideal time to change the spark plugs (if you haven't done that in the last couple seasons).

All cylinders should test over 100 PSI and all should be within 30 percent of each other.  So, take the highest compression number you get, multiply it by 0.7, and no cylinder should be lower than that number.

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Woodski

@85 Barefoot:  Problem is obvious, can't believe @MadMan & @csleaver missed the 2 items:  1. Nautique and 2. Ford. 

Okay, in all seriousness, they are pointing in the right directions, an easy test and from your description it seems that maybe the accelerator pump is not squirting any fuel, simply pop off the spark arrestor and give the throttle a twist while looking down the carb throat (engine off) and see if it has a good strong fuel squirt.  As the guys noted, sounds like a lean misfire when you give it a decent amount of throttle.  It also sounds like the choke is not working correctly if it needs high idle to stay running when first started.  My buddies Nautique struggled with the fuel pump setup, but his was injected I have no idea on how a carbed Ford PCM is set up, is it a mechanical or electric fuel pump?

Did this problem suddenly crop up and if yes, what was done just previous to the problem, that may help you trace back to a cause.  I always look back at the last thing I did as a possible reason for my new problem.

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85 Barefoot
10 hours ago, Woodski said:

@85 Barefoot:  Problem is obvious, can't believe @MadMan & @csleaver missed the 2 items:  1. Nautique and 2. Ford. 

Okay, in all seriousness, they are pointing in the right directions, an easy test and from your description it seems that maybe the accelerator pump is not squirting any fuel, simply pop off the spark arrestor and give the throttle a twist while looking down the carb throat (engine off) and see if it has a good strong fuel squirt.  As the guys noted, sounds like a lean misfire when you give it a decent amount of throttle.  It also sounds like the choke is not working correctly if it needs high idle to stay running when first started.  My buddies Nautique struggled with the fuel pump setup, but his was injected I have no idea on how a carbed Ford PCM is set up, is it a mechanical or electric fuel pump?

Did this problem suddenly crop up and if yes, what was done just previous to the problem, that may help you trace back to a cause.  I always look back at the last thing I did as a possible reason for my new problem.

Not sure whether we would have had this problem in the past or not, but this past weekend was just the first we slalomed.  Prior to that boat was getting plenty of kids duty (ie no hard acceleration needed).  So, it could have been there but we didn't know it.  We haven't done anything to it  recently other than repaired the fuel line connection to the carb which had developed a leak and the barb was damaged.  

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MadMan
11 hours ago, 85 Barefoot said:

.  We haven't done anything to it  recently other than repaired the fuel line connection to the carb which had developed a leak and the barb was damaged.  

This  may not be a coincidence.  Like maybe during this fix some trash might have gotten into the carb.

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85 Barefoot
29 minutes ago, MadMan said:

This  may not be a coincidence.  Like maybe during this fix some trash might have gotten into the carb.

ok...so dumb question, where would that trash congregate?

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MadMan
20 minutes ago, 85 Barefoot said:

ok...so dumb question, where would that trash congregate?

To cause a problem they wouldn't be just laying in the float bowl.  They would be in an internal passage, restricting fuel flow.  Carb would likely need to be disassembled to clean it out.

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