97 Challenger 787 rough idle, low to mid Accel hesitation

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Chadwicksracing

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Hello

Just bought this boat a month ago. Got her in the water over the weekend and found some issues. When I bought it we ran it for a a min, and it started.

So when it starts, it doesn't want to start takes some time to crank, then it runs very rough. Dies many times and mis fires. Once it's warmed up it idles fine at 1500.

Even you get it out on the water, and give it throttle, it takes a while to build speed and the engine hesitate. There is allot of white smoke coming from the exhaust. Once it's on plane and up to 5000 rpm, it runs and drives nice.

Previous owner said it ran last summer, and had the wear ring replaced.

I thought it might be bad gas, so I added fresh gas. Added seafoam.

I talked to mechanic, and he said it seen allot of gasket's leak in this engine. Crank or cylinder leak is what he mentioned. Telling me to spray crab cleaner on the gasket to see if it boggs or kills the engine.

So I need to trouble shoot. What is the do safest way to run this boat out side is water? I know you can hook a hose and run it with the water hose.

What you think? Carb issue, bad gasket or other issue. Before I pull the motor to get it rebuilt, maybe we can fix this...
 
You can run it for about a minute with a hose hooked up. Always start the engine before you turn on the water and turn off the water before you stop the engine. This is different than a regular boat.
Sounds like a carb problem to me. You should check the compression too.
 
Likely needs a thorough carb cleaning or a rebuild kit. It is 22 years old and may never have been done.
 
Good job! Those aluminum carbs make a squeaking noise while corroding if you listen very carefully on a quiet night.

After a few years or when hesitation begins to occur, just open them up and clean them out like you did. Get rid of any original grey fuel lines, something about the polymers in the rubber/plastic or metallic filler causes them to corrode and contaminate the carbs as well.
 
Good job! Those aluminum carbs make a squeaking noise while corroding if you listen very carefully on a quiet night.

After a few years or when hesitation begins to occur, just open them up and clean them out like you did. Get rid of any original grey fuel lines, something about the polymers in the rubber/plastic or metallic filler causes them to corrode and contaminate the carbs as well.

Thanks! Fuel lines are Black. Looked good when Carb was off.

Report:
1.The boat does not want to start with the choke on. Any ideas on that? It will start without choke fine.

2. Seems like I have a bit of hesitation on low-mid acceleration. Was thinking that RAVE values needs to be cleaned, or carb low speed is not set right (set to 1 turn from 0 per shop man) (Hi speed set to 0).

3. Water pressure valve on exhaust resonator is leaking. What is the remedy to this? What do I look for when trying to fix it?
 
If a cold engine floods easily with some choke, it sounds like too much fuel This results in the opposite of fuel starvation, it's not lean hesitation, it's pig rich, possibly.

The 1st course of action is to check the pop-off pressure, this can be accomplished without removing the carbs. If the pressure bleeds off rather quickly an/or cannot build pressure, the fuel metering needle inside the carb is leaking. This will cause hard starting and a very fuel rich condition.

FWIW, lean hesitation is a result of lack of fuel, commonly the engine will fall flat on it's face and suddenly quit just like it ran out of fuel, b/c it did!

4-stroking is a sign you're not experiencing lean hesitation (fuel starvation).


The water box valve has a rubber diaphragm inside, usually with a steel clamp to hold the inner diameter in place. This steel clamp often rusts then busts over time, and can tear a hole in the rubber diaphragm. So check the diaphragm for a small hole and if the clamp is rusted/busted a tie wrap can be used in it's place. Remove the wire bail holding the top cap in place and lift the top cap away. I'm pretty sure your water box valve is nearly identical to mine.

Also, if you can remove the tubing attached and unscrew the valve from the water box, you'll see it's a pintle valve that's operated by exhaust pressure. The pintle may be jammed with debris from the water supply so it may need cleaning to free it up and restore operation.

Let us know what you discover!
 
The PTO needle is is bad. When I did the pop off test, it didn't seal. But popped off around 29 psi, so I kept. Knowing that I would have to change it at the end of the season.

I bought a new set of plugs to tune in the carb. When I am up at the lake on the 4th I will put those in and do the low speed run..ect to the get a read on what the carbs are doing.

I will listen for 4 stroking.. :)

Will report back! Thanks so much for the info and help
 
Agreed, the rubber-tipped metering needle is the one part I always replace b/c a grove develops and the rubber is impregnated with a lubricant like graphite that wears away over the years. They come with a new brass seat and o-ring seal so I replace those for the benefit of the o-ring which can leak from age as well.

Be sure to order the correct seat orifice diameter else if it's not the correct orifice re-using the original seat is acceptable as long as it's not damaged somehow, IMO.

Good luck!
 
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