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fuel supply/fuel vent

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decsdad
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fuel supply/fuel vent

Post by decsdad » Sat Mar 10, 2012 12:13 pm

let me preface this with a huge thanks for the information/support this site continues to give, i only wish i could contribute in some way other than keeping a classic CC afloat and running.
boat: '70 17' corsair, 327Q
situation #1: the supply side of the fuel line just before the inline filter.
problem: the fuel does not stay under pressure, it drops down between start ups. this causes me to have to crank it a few times to "push" the fuel back up enough to supply engine. (priming the throttle does not take care of it)
any ideas/advice on how to keep the fuel somewhat pressured from falling back? -or is this the whole idea of fuel injection?
situation #2: the vent for my gas tank has no "saddle" or trap in the vent pipe causing fuel to leak out the vent on take offs. (lost half a tank on the trailer before the boat ever hit the water for the first time). sorry for no picture; the vent pipe is located at the top of the tank but then runs parallel to the rear vent so it literally flows straight out any time i take off. is it as simple as replacing the line with one that saddles or could that possibly be dangerous?
thank you in advance for any input...

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mfine
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Post by mfine » Sat Mar 10, 2012 4:44 pm

1) If I understand correctly, I don't think this is a preasure thing as much as a carb thing. Modern gas is more volatile than it used to be AND ethanol makes it even worse, so you are going to have evaporation out of the carb and if the boat sits too long, you will need to crank a bit (or quite a bit) until the bowl in the carb fills back up.

The solution I have chosen is to go to an electric fuel pump (with oil preassure shut off switch!) which can fill the carb bowls much quicker with less starter wear.

The cheap and keep it original "solution" is to crank with the throttle closed and choke on (should be auto on yours)WITH NO PUMPING until the carb bowls fill up. You may want to limit how long you crank without pausing for a minute or two to let the starter cool. Once the bowls fill up, you can crack the throttle or if you need to pump the throttle which uses the accelerator pump to squirt gas as a poor mans prime.

Another one I have seen people do is to keep a small bottle of gas on the boat and manually fill the carb. This is a bit of a pain and has a few safety issues, so I don't recomend it but thought I would mention it.

2) I had the same issue and decided to put the "saddle" in. Don't know if there are downsides I didn't think of, but I have not noticed anything yet.

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quitchabitchin
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Post by quitchabitchin » Sun Mar 11, 2012 9:34 pm

I have the '69 version. The fuel vent is a terrible design. I put a saddle in as high as I could and still leak fuel if the tank is completely full. I am going to make the vent hole a second bilge pump discharge, for a rear bilge pump, and install a modern clamshell style vent directly above the tank vent opening.

As far as the fuel goes, there are two shut off valves. One on top of the tank behind the rear seat and another in the line near the strainer. If you have to crank excessively between startups on the same day, it is not the fuel flowing back into the tank. There may be another issue. You could try pumping the throttle a few times before you turn the key as the accelerator pump will spray a little fuel into the intake and it may fire quicker. The fuel cannot flow back into the tank as the top of the tank, where the pickup tube connects, is much higher than the strainer, pump, and carb, therefore the fuel will not flow uphill. If you have trouble starting each time you go out, it is probably like mfine suggests fuel evaporating out of the bowl. I always close the one closest to the strainer just to make sure the fuel does not get sucked out of the fuel line due to expansion and contraction while on the trailer.
FLASH1969 Chris Craft Cavalier Ski-230 HP 327Q

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decsdad
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Post by decsdad » Tue Mar 13, 2012 8:38 am

thank you both.
the clamshell vent would mean having an additional piece of chrome on the body, correct?
that seems to be a simple enough solution especially if you say the saddle didn't work. you saved me some heartache, thank you!
i'm looking into the electronic fuel pump.

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quitchabitchin
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Post by quitchabitchin » Tue Mar 13, 2012 8:11 pm

Just to give you an idea of how poor that design is, last summer we were fueling up at the dock and a rather large friend was sitting in the rear seat on the starboard side, right in front of the vent. The dock boy kept pumping and pumping until there was fuel gushing out of the vent. It continued to gush out until I told my friend to stand up and go to the other side or the middle. It finally quit pouring out into the water after he stood up near the engine. We probably lost a gallon or more of gasoline...not only is it a fire hazard, bad for the fishes, but it was also pushing 5 bucks a gallon.

You can use the modern mini clamshell or there is also a chrome round vent available as well. Just make sure you do something with the rear vent hole or you will take on water as the boat rocks or when you slow down. If you want to leave it there, you could attach a cap to the inside of that fitting. It's pretty tough to reach over the fuel tank, it just takes a little patience and long arms.
FLASH1969 Chris Craft Cavalier Ski-230 HP 327Q

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Paul P
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Post by Paul P » Thu Apr 12, 2012 8:33 am

With that much fuel loss you have a very serious problem. I would seriously consider a check valve in the vent line, or run the darn line forward to another location because it makes no difference where the vent is as long as it functions. The problem is, if it gets fuel in it at a low spot in the line it may act like a p-trap in your bathroom and keep the tank from venting properly. In any case, with fuel loss like that you need to tend to that issue and fix it, because that is totally unacceptable in any boat.

Also the cranking, sounds like you have Carter AFB carbs. They are NOTORIOUS for drain-back, evaporation, and literally cooking on top of an iron intake manifold. There are some purists I know who go after that little brass check valve on the bottom of the fuel bowl on a Carter, that does not appear in the rebuild kits, and they claim this will stop the drainback or whatever is actually happening to the Carters. Those carbs run well when they are being used regularly but if the boat (or car) sits very long they require cranking. Also I have discovered the chokes on these Carters don't want to close as far as they should, and if you hold one tightly closed a motor will jump to life with a full choke charge. The electric fuel pump idea is valid, but only if connected to an oil pressure switch acting as a safety disconnect (very common system for electric fuel pumps on boats).

regards,

Paul
1956 17' CC Sportsman, 300-hp
1957 17' CC Sportsman, 95-hp
1966 20' CC fiberglass Sea Skiff, 210-hp+
1973 23' CC Lancer inboard project, 427/375-hp.
1966 38' CC Commander Express, 427/300-hp(2)

So many boats.........so little time.....but what a way to go!!

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quitchabitchin
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Post by quitchabitchin » Thu Apr 12, 2012 8:35 pm

The carb would be a Carter AVS. With the intake design, there is no crossover, and the intake is actually pretty deep at the center point, so I doubt fuel is boiling or evaporating from heat. It could be but it doesn't seem as likely without the crossover.

The saddle I put in is basically an upside down P trap. The vent tube is standard 1/2" copper, so I pulled the line, measured out some fittings, marked it and sweated it together. I plan on attaching a flexible vent hose to a new chrome fitting on the back of the boat, just above the vent opening. I am going to put a second bilge pump with a float switch in the rear and attach it to the current vent fitting. When the front bilge pump is working, there still seems to be quite a bit of water in the rear of the boat when you take off. Chris Craft had an issue on these boats with the seal between the deck and hull, so when you make a turn, water runs down the sides into the hull. I am going to seal this better, but want to be sure if ay water does collect in the bilge, it will be pumped out upon takeoff.
FLASH1969 Chris Craft Cavalier Ski-230 HP 327Q

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Paul P
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Post by Paul P » Fri Apr 13, 2012 9:42 am

Yes the comment about no crossover is valid for sure, but the iron will still get hot due to heat soak and being bolted directly to the cylinder heads. The cranking and starting is one issue, and you might try my trick of holding the choke fully shut and see what happens, if it starts right up then that old style Carter choke furnace and thermocouple may need adjusting, or you could just install a manual and be done with it.

On my 38 Commander my 427 engines need a lot of coaxing before they start, unless I hold that choke fully shut. The older the carb the more air leaks in around the shafts, so what used to be a full choke is no more on some of these old carbs. I am considering a manual system that I can reach easily upon lifting the engine hatch, as I always lift the hatch and sniff for gas vapors as a habit anyway. At that point with hatch open I can activate the chokes, start up, let engines warm for a moment, shut off the choke and close the hatch. Another good thing about that would be you would always knwo the choke was fully open too.

Hope your venting works out okay, it is a serious issue. As for the bilge pumping, remember the vent tubes the wood speedboats use? Once running you never have to even think about a bilge pump unless you are really taking on a lot of water. One of those would be a functional feature.

best,

Paul
1956 17' CC Sportsman, 300-hp
1957 17' CC Sportsman, 95-hp
1966 20' CC fiberglass Sea Skiff, 210-hp+
1973 23' CC Lancer inboard project, 427/375-hp.
1966 38' CC Commander Express, 427/300-hp(2)

So many boats.........so little time.....but what a way to go!!

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