Fuel system question

[parrott04]

Ok I need help I have a 1964 41 DC that I have had a problem with now for weeks I bought the boat last year as a project the boat had been a liveaboard untill Isbel set it on a dock so it had not run in at least a two years am not sure how long before that, it has gas motors that run out of fuel I have rebuilt the carbs built new pick up tubes pumped all the old gas out and replaced the filters an cross over valve and replaced the copper piping with hose from the bulkhead to the motors with new filters and valves you can prime the carb start the motors and sitting at the dock they will run forever you can untie the boat clear the no wake zone power up the motors and it will go about 200 yards and one engine will start missing and then die and it will be have no gas in the carb not sure what to try next.

[mike]

Need more info to do a good job of trouble shooting. When you say new pick-up tubes are your referring to the carbs or the fuel tanks? Are the tanks the std Hatteras GRP units? Assumining you have sufficient fuel on board and the filters are not plugging up, I would confirm that the fuel pick-ups in the tanks are ok and not being covered by some debris. Something may be coverning the tank pick-up as you power-up. Another test is to setup temporary tanks (6 gal plastic outboard tanks will work) and validate that the fuel system is working from the temp tanks and new hoses to the engines. Does this happen to both engines? If not have you tried switching between tanks? If you switch between tanks does the problem follow? As you know this becomes a process of validation and elimination of each component as the root cause. FWIW, I would draw a schmetic of the system with each component, isolate and check each, working back from the carb, assuming I could get the boat to run on the temporary tanks. You did not mention if you replaced the fuel pumps? Sometimes pumps will draw sufficient fuel for non-loaded conditions, but under load fail. Also make certain the fuel lines from the tanks to the shut-off valves are not leaking, a little air leak in the line can be a problem under load, but not at idle. Check the fuel pressure, it should be at least 4 psi or greater.

[MikeP]

All of Mike's points are excellent.

I went through an almost identical situation a couple of years ago. It ended up being fuel tanks with a huge amount of cr@p and sediment that was clogging the fuel filters AND check valves quickly and completely. It would run forever at the dock/idling out of the harbor but would not run for more than a few minutes under power. Check your filters and check your check valves. If there is a lot of stuff in the tanks, the check valves will also clog and restrict the fuel flow to nearly nothing even if the filters remain fairly clean.

When I discovered the problem, I made a a portable fuel polishing system using a holley fuel pump and a gulf coast F1 filter. I vacuumed the bottoms tanks with the unit, polished all the fuel, and I never had any further problem.

If it turns out that your problem is the same thing, let me know and I can give you some more details on the specifics that worked for me.

[67hat34c]

What engines do you have?

regarding fuel pumps, look at the overflow bowl or overflow tube comming from pumps, if there is gas in there then the pump is shot. if pumps are gone then convert to electric fuel pumps.

trace out the entire fuel system look for added filters and check valves along the line.

clean out fuel tank, i like the idea of the portable fuel polishing system. would like to make one of my own. Mike can you provide more info on your system

[Pascal]

can you try to increase the load only on one engine, letting the other one idle? maybe with a few passengers at the bow to minimize bow rise? if each engine can sustain the load, then it means that you have some "stuff" in the tanks which is moving back to the pick ups as the bow lifts.

[MikeP]

Here is a picture of my portable fuel polisher. It consists of a 12V holley 87GPH fuel pump, a Gulf coast F1 filter, and some hose and clear tubing with a copper tube "wand" on the input end.

You can use the wand to vacuum the bottom of the tank, working it all around as best you can through whatever openings are available in the top of the tank. The clear tubing will allow you to see what is going into the filter and what is coming out.

The best way to do this, if you are lucky enough to have less than 1/2 tanks of fuel is to vacuum the bottom of tank 1 until you get no more cr@p and then pump the remainder of that fuel into tank 2. Then vacuum tank 2 and pump all the fuel through the filter and into tank 1. If you can't split them that way, just vacuum one tank, with the return line running back into the same tank.

It may take quite a bit of vacuuming with the wand to get all the junk out. You might be amazed at the black gunk that is in the tanks. The larger the tubing size you can use, the better. I used 3/8 but I will replace it with 1/2 the next time I need to use it.

There are probably cheaper filters that will work well but the F1 has a very large capacity for trapping water compared to smaller filters.

[hcalmar]

I have a friend who was vexed by a similar problem for a whole summer after he repowered. Turned out the new pickups were too close to the bottom of the tank and starved the engines as he powered up. May be worth a check. Hal

[parrott04]

Great ideas, thanks I did build new pick up tubs in the tanks the ones that were on the boat were cracked and rotten what they looked like they were just a peice of 3/8 copper and a male fitting that screwed into the tank I am not sure there are any check valves in the fuel system I have thought about 12 volt fuel pumps is there any thing I would have to worry about with them and what kind would I need to look for the motors are 440 several things in the other post would make since I did replace all the piping from the bulkhead wall foward and I also replaced cross over valve with newand new filters that took out a lot of screw fittings and now are barb fittings with clamps I will try new fuel pumps maybe pull the pick up tubes out and take another 3/4'" off of them also will try the 6 gallon fuel tanks and see how it runs with them, I will update if we find out what it is........ Thanks for all the ideas.

[MikeP]

If the top of the fuel tanks are above the level of the carburetors, check valves are required to eliminate the possibility of fuel syphoning out of the tank. However, the requirement doesn't mean they are there. People often remove them to incorrectly solve fuel delivery problems associated with dirty tanks. But without them, the only thing keeping the engine and boat from filling with gasoline is the needles and seats in the carburetors. A fuel-logged float or a particle of whatever between the needle and seat will allow however much fuel is in the tank above the level of the carb to drain into the engine. When the cylinders with open intake valves are full of gas, the intake manifold will fill. When that's full, it will spill into the bilges...

12V fuel pumps will work fine. There are many to choose from. Be sure it is ignition protected. Wire it so it will not run if the engine is off. Typically it is wired through an engine oil pressure sensor switch. Until oil pressure comes up to 10-15psi, which it will while cranking, the pump will not run.

Remove the mechanical pump and put a block-off plate on the engine boss where the current pump is attached. If you want to be able to run the pump with the engine off to prime the system or whatever, you could install a spring-loaded momentary-on switch to supply power to the pump, bypassing the oil Press switch.

[Vic Clevenger]

Hi parrott04. A few years ago I had a similar problem in my 454 powered 86 sedan cruiser. It would run fine at the dock or anywhere at idle. But when powered up, one engine would starve. I was on a cruise and away from my home port. An older, retired boat mechanic was summoned to help me. The first thing he said was "older Hatt with gas engines, I bet it is the anti-siphon valves". He pulled them out and sure enough they were clogged with fiberglass shavings (hairs) from the tank. He blew them out with compressed air, dried them, re-installed, and everything was fine. They are located just past the shut off valves on top of the fuel tank. My boat has three of them, one for the port engine, one for the starboard, and one for the genny. Just a thought, it could be these check valves. Vic Clevenger
1986 SC