Carver 356 RPM issues

[390Express]

Source of the post 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.

I could be wrong, but I think what Bud is trying to say, is that a sticky valve (tank selector valve) could allow air into the system, even if it is not wet or leaking. The introduction of air into your fuel system will cause a fuel starvation issue.

Have you replaced your fuel lines yet?

Also, to CPs point, if you install a small tank to run off of temporarily, you will have to run the return to the small tank also. I set up a 5 gallon tank to feed from, and left the return to the main tank hooked up. The return line emptied all 5 gallons back into the main tank in about a minute and a half, and I have a low pressure (12psi TBI) system. Mine wasn't complicated, I literally left the cap off of the small tank and just dangled the return line back into the small tank, and it worked fine. I did have someone standing near the engine bay and the engine bay open while running. It probably isn't the safest means of operation, but it was well ventilated, and I was only set up that way to test an issue. I ran the boat 2 min. down the canal, to the mouth of the marina, turned around and came back. Everything worked fine.

[bud37]

He has MPI, dont believe there is a return line.

[km1125]

Really do need a good summary of the current symptoms/issues.

But, based on what you said in these posts:

Source of the post
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.

This sounds like a fuel pressure problem. I would get have a gauge hooked up to the fuel rail and check pressure BEFORE you start, after you turn the key on, and then after it starts and runs. Also, you might try to cycle the key on two or three times (then leave off for ~10 seconds in between each) to let the fuel pump pressurize the system and see if that makes a difference after you start the engine. If it does, then the fuel pressure is bleeding off when the engine is off.

Source of the post
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.

This does sound like the engine is being starved of fuel. Either it's a flow problem though the filters getting to the engine, a bad fuel pump that can't keep up with engine demand, or too much fuel being diverted back to the tank. Running with a pressure gauge on the fuel rail will help ID it, but it would also help to have a vacuum guage before the pump (and after the filters) to see if you're dropping pressure there.

[cpoint]

km, Thanks for all the info. I will get those checked out and reply back here.

[Viper]

Source of the post.... if you install a small tank to run off of temporarily, you will have to run the return to the small tank also.....

Source of the post He has MPI, dont believe there is a return line.

Technically there is a fuel return circuit on these but it gets returned to the fuel filter housing, not the fuel tank unless the OEM has specifically asked Merc to set it up that way. If the retrun is to the filter houising as is the norm for these, you don't have to worry about setting up an extra line to the portable tank, just a feed line. I would not use any existing line in the boat. Disconnect the boat's feed line to the filter, and hook up a known new line from the tank to the filter. That eliminates the boat's system completely.

[cpoint]

I got a new mechanic coming by next week. I passed on all the info and what I got here from you all. But before I did, he said he was bringing his own tank to eliminate fuel tank/line issues to start with. So keeping fingers crossed... I'll update this issue next week after I meet him.

[Viper]

Does he have Merc diagnostic software to see what the engine's doing in case it's an engine problem?

[cpoint]

viper, not sure. he was recommended by a friend who is been using his services for many years. Although previous company I had working on it is mercury authorized legit company. I had it checked out with them since they been working on it past 3 years on and off. they claimed nothing out of ordinary showed up. Last I worked with them engine was was OK according to them. So we'll see if this is fuel side issue.

[390Express]

Because we seem to be having similar problems, here's an update on my issue. (will update my thread as well)

I went ahead and added a 2nd can style filter, in addition to the Oberg fuel filter. After adding the can style, I can that emphatically that I believe the can to be superior in virtually every way to the Oberg filter. In a perfect world, the Oberg works, and it has bonuses (easy to take the screen out and have a look at what's going on), but the can style filter is much, much more effective, and acts as a water separator, whether it's branded that way on the filter or not. I'm currently using FRAM EXTRA GUARD PH8A oil filters for $3.99, and they're working wonderfully. I'll edit my post to add pics of my setup, but it's worked great. In addition to sediment, I have found that I still have small amounts of water in my system, even after draining the tank twice and refilling with stabilize, enzyme treatment, and 30-40 gallons of good gas.

I've been cautioned on here about running two filters, and did not want to do it for a number of reasons, but read that it is perhaps necessary on the WIX page, whom seemed to provide an endorsement of the same. I know - Wix sells filters, they'll tell you anything, right? Well, they could say to eliminate your old system and install theirs, but the actually recommend adding a 2nd filter. After adding the 2nd filter I can now run my boat for about an hour and half. It's the size of the filter vs the Oberg that makes the biggest difference, and I love that the can style is trapping more water than my prior filter. (water was getting past my prior Oberg filter, and causing me RPM issues) Motor used to hesitate and sputter around 3000 RPM. I believe that was caused by the small amount of water in the gas. Now it rpms to 4000k no problem, and I'm confident that it will hit 4,500 if I ask it to. Ran the motor for about 5 hours last night. I had to drain the fuel filters of water twice, but was able to recycle them more or less (turn them upside down, and drain out the water and gas, and use them again). I plan on keeping 4 of them on the boat for when I'm out on the lake, but it's running for over an hour with its current setup. The extra filters are more precaution than anything.

If you don't have a can style, I would recommend adding one asap. Pics to follow. The system that I installed required no bolts, no modification, and can easily be switched back to the factory configuration in 10-15 miuntes. After running 40-50 gallons through it, I think I'll try going back to the Oberg alone. We'll see.

[km1125]

The Oberg is not really designed to be a good filter. Only good enough to protect the front-end low pressure pump from debris that could damage the pump. If you have mechanical pumps, that's not really a big issue, nor is a slight increase in the resistance from the tank, as a mechanical pump can overcome that much easier than an electric pump.

A screw-on filter probably has 10x the filtered area compared to an Oberg.