Fuel shutoff

[Helmsman]

I have a 2006 Carver 33 SS with Crusader 6.0 l gas engines installed. I am planning to replace my fuel filters. My port engine rpm's are cycling up and down, up to 300 rpm's when I accelerate from 1000 rpm's to 2500 while underway. Once I reach 2500 the problem seems to "go away". In neutral, I don't have the same problem. I have read in other forums that the filters may need changing. If anyone here has other ideas or thoughts on the problem I would appreciate it.

I have studied how to change both the pre-filter and the water separator filter in the Crusader manuals. I have a returnless system with a Racor 110 AT separator which uses a Crusader 47047 filter. I feel pretty comfortable changing the filters except for one issue I can't seem to get an answer for. I traced the fuel supply line back to the tank. I don't see a manual fuel shutoff valve anywhere. Perhaps I am missing it, but in reading some forums, the answers aren't clear. Is there something I need to do to keep the fuel from siphoning out?

Before I install the filters, is there anyone here who could help me with this question?

Thanks!

Nate

[bud37]

Hi Nate......our boat does not have shut offs either, I thought the same as you but changed the fuel sep filters on the mercs with no drama other than the usual towels, zip lock bags and try not to spill fuel and be very safe ( power off 12v/110 etc). These filters are fairly low on the engines.I guess you could have a pair of vice grips handy to pinch the fuel line shut if need be.There actually should be an anti-syphon valve at your fuel tank connection,it is just the fitting with a spring and check ball affair the stops the fuel syphoning to the bilge in case of a leak, which if plugged can cause some interesting issues.
At some point I will be adding shutoffs at the tank,its on the list...lol........

[Viper]

Correct. You'll may get some fuel draining back that's in the lines but the purpose of the anti-siphon valves is to prevent siphoning. You need more vacuum than just a siphoning action to overcome the valves. Having said that, this safety system only works if the valves are working properly. Some vessels won't have manual shut off valves, some will, and some will have electric ones but unless the vessel is really old or a previous owner has removed them, there should be anti-siphon valves.

Don't pinch the fuel lines. The newer standard line (ethanol safe) has a plastic inner wall that you'll crush if you do.

Ventilate ventilate ventilate!

[Helmsman]

Thanks. Looks like there is an anti-siphon valve. In the manual it mentions a fuel shutoff valve, but that is where the anti-siphon valve is. I will have the engine compartment wide open, the 110/12 both off and take my time. Appreciate your help. Hope this fixes the issue!

[Helmsman]

Ok. Was able to change the fuel water separator filter. The port engine fuel in the canister was dark grey, so I am hoping that fixed it. Also noticed some transmission fluid leaking from the port transmission. That may also have something to do wit it. Am going to take the boat out later for a spin to see if the erratic RPM issue is fixed. I changed out the transmission cooler on that transmission last fall and am hoping that caused the leak. We will see.

[bud37]

Qr Bbpost Ok. Was able to change the fuel water separator filter. The port engine fuel in the canister was dark grey, so I am hoping that fixed it. Also noticed some transmission fluid leaking from the port transmission. That may also have something to do wit it. Am going to take the boat out later for a spin to see if the erratic RPM issue is fixed. I changed out the transmission cooler on that transmission last fall and am hoping that caused the leak. We will see.

Question for ya....have you recently started using fuel with ethanol, or has marina switched..maybe you just filled up before this started.....??

[Helmsman]

Bud, we have ethanol free fuel here on lake chickamauga. I did top off the tanks (both of them) on our first trip this summer. Could certainly have been bad gas. So, the erratic RPM is fixed with the fuel filter change.

However, the vibration problem on the port engine is still a problem. It is the transmission I think. I will start a new thread.

Thanks for the help, everybody.