Unfortunately in the cyberspace day and age, a click of a mouse is all it takes, and once you do it, the thread is Gone with a capital "G". Your nice post about check valves, siphoning, 600 cfm carb on a 350Q, etc., was mistakenly deleted when I intended to delete my own post in order to edit it.
You installed rubber hose on the tank side of the fuel pump due to your research indicating it's okay to do so if it withstands fire for 2 minutes. You installed check valves to avoid anti siphon back to the tank. Your 350Q will run much higher rpm than most of us are willing to run, so we're interested in how you do this and why.
The comments about bilge are good, please eleaborate.
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Here's what my post said, too bad yours isn't here any more, very sorry, Please post again!
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This is a generic photo of a 350, feel free to send in photos of your boat and the motors!
You don't have to have a Commander to post here, (you don't even have to have a boat or a name!)
Your comments are appreciated, as they help build a database for all Chris Craft engine diagnostics, etc. The fuel obstruction thing is pretty common these days, many of us have either experienced it directly or know someone who has. The shut-off valves are suspect, but so are those check valves you installed. Yours are new and work fine, but I know a guy with a fairly new boat and his have given him a lot of trouble, as they represent an obstruction that apparently can (and did) collect debris and form a blockage. I guess it depends on whether they’re on the tank side or motor side of the filter.
The comment about fuel siphoning back into the tank is VERY INTERESTING to me. Tell me more. Is that prevalent with mechanical pumps and carb systems? It would appear on my boat that the bottom of the tank is lower than the carb, in which case siphoning while sitting over a period of time could be an issue.
Regarding your Catalina, I think (not sure) they share the same hull as a Commander from the waterline down to the keel. Changes may have been made from the water up, in order to make them a one piece casting. Hopefully someone who knows the answer will chime in on this one, as we need some sort of a link between the Commander and Catalina.
Calvin, if you asked about using rubber fuel hose, it is OK to do so as long as you use USCG Type A1 hose (it will have a red stripe along one side, and say USCG Type A1 every foot or so).
Here is a picture which I posted before of some mods we did to our fuel system -- the hose you see is that Coast Guard approved red-stripe hose, and the fuel pumps are marine rated:
I am interested in the anti-siphon topic. Our boat is a Sportfisher model which has a lower cockpit floor than non-SF Commanders. Since the fuel tanks are located under the cockpit, the tops of the carbs are higher than the tops of our fuel tanks. Our new Carter rotary vane fuel pumps have no built-in check valve -- when you turn the engines off and the pumps quite running, there is nothing to prevent the fuel from draining back into the tanks. Air can get in through the carbs on the main engines (and/or the genset) if the carb floats drop a little due to boat rocking or fuel evaporation. As soon as air gets in, the whole fuel empties itself back into the fuel tanks.
This is not all bad -- it is kind of a good saftey feature. But it does complicate things a bit. As you can see at the top of the picture, I added a fuel pump priming switch to the system so we can manually prime the fuel system -- that way we don't need to run the engine starter for 20 or 30 seconds while the fuel lines prime. But things would be easier if our fuel lines didn't completely drain back to the tanks so often.
If we had mechanical fuel pumps, or even diaphram electric fuel pumps, I don't think fuel could flow backward through them due to the internal check valves inherent in their design, and we wouldn't lose our prime.
I think I am going to add some fuel pressure regulators just downstream from the fuel pumps. Not only will those positively regulate the pressure to a safe 6 psi (our pumps now can put out slightly more than that), but I believe (but I do not know for sure) that the pressure regulators will also serve as a backflow preventer, so our fuel system will hold its prime.
What has got me thinking about this topic lately is we had our main engines off and tried to run our genset the other day. It ran for a short time, then slowed to idle speed -- and the speed couldn't be changed by manually changing the genset throttle position or even by running the choke fully closed. We turned off the run switch, and took the carb off the genset engine to see if it was obstructed. I found the carb bowl didn't have a drop of gas in it. Now I was really baffled -- not only was the genset running at idle and wouldn't yield to manual throttle control, but it was doing that on no gasoline! I finally realized that the genset wasn't really "running" -- it was just being spun over by it's starter, which I think is direct drive via a starter winding in the generator. That starter doesn't make a sound and is so smooth that you really can't tell it is running, and the genset engine appeared to be running at idle.
The reason the genset quit running was that the fuel had all siphoned back into our fuel tanks, and the little genset fuel pump couldn't suck hard enough re-establish the prime. Once I ran my manual priming switch and wetted up the fuel lines, the genset started right up and ran fine again. This is the event that has caused my current interest in the anti-siphoning topic.
I'll keep you-all posted. If anyone has any thoughts, I'm all ears.
Best wishes, Curt...
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1967 fiberglass 38' Chris Craft Commander Sportfisher with twin 427 CID 300 HP engines.
Once again, please remember that I am no mechanic.
Anti-siphoning valve: If you’re going to install them, there should be one per fuel line. As per you picture, you would need three. Install them as close to the tank as possible. This will keep the maximum amount of fuel in the lines at all times. Yes, I have heard of them jamming up occasionally. I view this as a minor problem. I would rather replace a $2 piece and solve the problem, than tearing apart an entire fuel system trying to figure out why I can get gas to the carburetor.
Fuel pump mounting: My fuel pumps are mounted on top of the motor. It looks like we may be using the same kind. Mounting them on top of the motor helps them work better. Most people forget that although the pump is pulling fuel though it, it is also pushing fuel out of it. Pumps are designed to pull fuel. If the distance from your fuel source to the pump is less than the distance from your fuel pump to the carburetor, your pump is pushing. Most pumps do a good job of both pulling and pushing fuel through the line. Unfortunately, in this situation, our older boats were equipped with mechanical pumps that were stronger and could handle pulling fuel from the tank and pushing it the full length of the boat if necessary.
The Smell: On my boat 1978 Catalina 350, there are hollowed out areas underneath each engine that are designed to keep anything from falling/leaking from the motors, (Oil, fuel, broken spark plugs), from getting into the central bilge. From time to time this area gets something in it. Like any part of the bilge, it should be kept clean. Not sterile, just clean. Use some simple green or any non-corrosive degreaser. I have heard that foaming carpet cleaner works well. Spray it on, let it set for a few minutes and wipe it of. If you’re worried about any chemicals eating your hull, Rinse the area with clean water.
Carborators: Edelbrock 4 barrel 600cfi marine carborators are expensive. If you buy them retail from a marina or dry dock, the are about $490 off the shelf. Search the internet, You can probibly find them for half of that. This was a hard lesson to learn.
If your curious about mounting the fuel filter on top of the engine, let me know and I will get some pictures for you.
If you have any more questions, don’t hesitate to ask.
Here is the repost requested. Paul, no worries about the accidental delete, accidents happen.
From 28 June 2006.
I have read all your threads and laugh because I have experienced all of these problems, every single one of them. My engine knowledge is limited to the fuel spark rule but I learned a few things.
Engine stalls out after running for a while:
1) I solved this by simplifying things. First I removed the fuel filter and water fuel separator from the area between the transom and the engines. Chris Craft is notorious for overkill. I own a 1978 Chris Craft 350 with dual 35Qs. At the aft of the boat, above the fuel tanks, there are giant fuel filters. Then there is hard-line all the way to the transom. There are three shut off valves at the tanks. Then from the transom to the motor it goes (Shutoff valve to the water fuel separator to another smaller fuel filter to another shutoff valve). Pulling all that out solved the fuel flow problem. I did some research and from the transom forward you are allowed to use soft line as long as it is USCG A1 which resists fire for 2.5 minutes. I replaced that junk and whalah, no more fuel problems.
2) I replaced my mechanical fuel pumps with electrical pumps. Most fuel pumps only pull about 7 psi. The mechanical pumps were better but they are old and I had to replace one anyway. I also installed flow stopping valves at the tank. This keeps the fuel in the line when the motor stops pumping, not allowing the fuel to reverse back into the tank.
3) Lastly, I replaced the original carburetors with Edelbrock 600 cfi marine carburetors and set the idles at 900 rpm.
I haven’t had a single problem with it since I made these changes.
I have had the motor to 5500 rpm. I agree that 3500 should be the max you push your motor. But having the extra power to maneuver with when you need it is nice.
The smell - Sir, without sounding disrespectful, clean your bilge. To be more exact, clean the areas under your motors. Chris craft built little divots under the engines to keep engine seepage from getting into the central bilge. This is great for containing the seepage but awful for the hull and for the smell of your boat. Get some degreaser and put it under your motors. Cleaning out that area will get rid of most of the smell. The smell reminded me of an old greasy auto shop.
I really felt bad about deleting your post, thanks for reposting it. With computers, it always pays to think again before you hit the ole delete button!
In the "Sawdust in Fuel Tank" thread of May 4, 2006, I posted "fuel plumbing specs and other stuff" with USCG and ABYC specs for gasoline powered boat fuel systems. These specs are quite specific about fuel line materials and electric fuel pump installations - especially the wiring and the placement of the pumps. Read carefully.
Bertram used check valves in the fuel supply lines of their gasoline powered boats in the 1970's. I've never seen check valves on a Chris-Craft.
The check valves I made reference to were in a Bluewater Yacht, with big block gas power. The boat is essentially "in new condition", not really my cup of tea, but an expensive boat with low hours and lots of interior space.
The check valves were of a design that over a short period of time apparently collected debris and became clogged. He went through the whole routine, coils, filters, etc.
The symptoms were, fine starting from cold, good running for a couple miles and then at the same general location along the route, one engine would sputter and would still run but would not come up to power. He thought it was heat related, but apparently it took that long for the remaining opening in the fuel passage to become constricted.
Once they tossed the check valves, no more problems.
One wonders however, why the check valves were there, and if they provide a particular safety feature for that particular design.
I can see him in a future survey, looking at the report "NO CHECK VALVES", ha.
