Carver 356 RPM issues

[Viper]

I don't recall if you did this or not but some time ago ( I believe last year) I had recommended isolating the engines from the boat's fuel delivery system by hooking up a portable fuel tank directly to an engine. In doing so, if the engines act the same then you're wasting your time and money with the boat's fuel lines as the fault would be the engines. If they run fine on the portable tank, then the issue is the boat's fuel system and not the engines. Has this been done yet?

[cpoint]

Viper, Thanks. I was going through this long thread at this point, which I had promised to summarize and restart a clean slate, but did not get a chance. but in any case, I did see your message and had not done that. I need to get one of those tanks. I assume 10 gallon should do? So task would be to close the fuel line at the switch (OFF position). unhook the fuel line from switch and hook to the external tank, is that correct?

[km1125]

Just remember, if this is a fuel injected engine that has a return line to the tank, then either the return line should also go to that temporary tank, or you need to be aware of two other things: 1) that fuel economy will be much less (because the extra fuel is going into the original tank) and 2) that the original tank has enough empty volume to carry most of the fuel in the portable tank. (to make sure there's no possibility of overflow)

[cpoint]

km, economy is not an issue at this point, I just want to remove the fuel line from my list. I took the boat out this weekend, as long as I am going about 2k RPM (about 8 knots), it was fine, smooth ride. The other thing I can say is, when I start it first time of the week (as I get to it on the weekends), after not using it a week, the engine turned over nicely, but then dies even if I give it gas slight before it dies. Usually it take a 2-3 more tries than its all fine. It feels like the fuel is drained from it? but once it is started it will start fine next time in the same day. Any ideas what that would mean. That's why with lack of my mechanical knowledge, it made sense there was an issue on the fuel line, that it was not having fuel in the line enough and took few tries for it to get it going. Which is also made me assume that after 2k RPM it was not maybe getting enough fuel. Because after 2k RPM, if both engines are reved up starboard uses much more gas and I can feel it start pushing towards port side, so I compensate to starboard via steering. since last fill up I ended up using 1/4 tank more fuel on starboard then on port side, mostly it was 2k RPM, and there was some 2.5K RPM where starboard definitely ended up using more fuel. Again there is no difference in the engine noise as far as reving strange when it is over 2K RPM.

[bud37]

Can I make a small suggestion.......because this thread is very long, we have lost track....if you could post your engine make ( black , blue , red ), size, hp, whether EFI, multi port injection ( MPI ) , perhaps a serial number of one side ( port or stbd )...thanks man, this could help the guys on this stuff.I apologize if you have, I just didn't see it.

[cpoint]

Bud,

Info below is from survey report

Model: 356 Motor Yacht --- Length: 41’2” --- Year: 2000
Engines Information:
Engines make: Mercruiser
Fuel type: Gasoline
Engines model: 454 MPI
Induction: Natural
Engines serial #: Port: 0L-393265
# of cylinders: 8 Rated
horsepower: 310
Rated RPM: 4400/4800
Injection: EFI
Engine hours: Port: below 600
Fuel primer pump: N/A
Alternator: 12 volts
Transmissions: Velvet drive Model: 20-01-005 Ratio: 2.45 to 1
Transmissions serial # Port: 6241
Stuffing boxes: Dripless Condition: No leaks noted
Engines oil level: Correct
Transmissions oil level: Correct

Fuel Tank Filters and Fuel Hoses:
Tanks construction: 5052 Aluminum Tanks
location: Engine room
Tanks capacity: 350 gals
Injection pump type: Electric
Fuel Delivery: Flex lines and formed steel
System static suppression: yes
System bonding: Available
Main engine fuel filter: Spin
Venting system: Overboard Fuel fill hose: A 2
Fuel manifold valves: Operational (Binding)

[km1125]

My point about the 'economy', wasn't really about 'economy'. If you were testing on a 10 Gal tank and thinking you could go 5 miles to test, you might be surprised that you empty the tank, as some of that fuel is going past the regulator and into your main tank. Just something to keep an eye on when you're running the test from the temporary tank, if the return line is still going to the main tank.

Also, did you ever check your tanks and the fuel pick-up tubes. I'm sure I posted this before, but there was an issue with some early 356 tanks. The tanks were aluminum and the pickup tubes copper. After a while (and might be dependent on environment and fuel), the copper tubes would begin to oxidize and the particles would end up in the fuel line. If you get the numbers off the tank and contact the manufacturer you might be able to rule that out on yours.

It would be good if you reposted the symptoms/observations and KNOWN results of tests so far. Reading different threads makes it hard to keep the symptoms straight between the different issues different folks are having.

[cpoint]

km, I recall last time they were cleaning out the tank, they told me lines were clean. Not sure how they checked. The other thing, again, if that's the case, when I switch to aux, it should not be an issue. Because aux feed to starboard is perfectly fine. Unless there are 2 feeders from aux, separate for each engine when selected?

[bud37]

Source of the post km, I recall last time they were cleaning out the tank, they told me lines were clean. Not sure how they checked. The other thing, again, if that's the case, when I switch to aux, it should not be an issue. Because aux feed to starboard is perfectly fine. Unless there are 2 feeders from aux, separate for each engine when selected?

In any situation where you have the choice of multiple tanks etc , you need to be sure of what orientation the fuel feed valves are in........I will give you an example.....say you had two tanks with the choices on the valve being #1, #2 or both......now if # 1 tank is empty and that feed valve was partially on #1 or the both position that would pull air from the empty tank and create havoc for the engine , the valve would have to be clearly in the #2 position.

So after saying all this, it might have nothing to do with your case, but I did notice on the report you posted that the surveyor reported that the fuel manifold valves were binding, I have been thru this before and I can tell you they will pull air without leaking fuel, so well worth checking....again, good luck, hope you find your problem and thanks for posting the numbers.

[cpoint]

Bud thanks. I mean at no time my tanks are completely empty. AUX tank has maybe 25-30 gallon fuel in it and port and starboard also same. However, any idea why the initial start does not keep on port side. I mean engine turns over, 2-3 seconds later it dies, even if I try to give it gas to rev it up it wont do it. 2nd or 3rd attempt it will start and stay on, or I may assist by giving a slight gas as it turns over and I notice it seems to be about to shut off. I mean it definitely looks like a fuel issue but what do I know But you are correct, I do have the switch in correct position. Unless the switch has some issue not opening perfectly and not enough fuel flowing through.