What could it be?

Dry Run · 11 July 2016, 08:41

Hi,

Just posting this in case anyone else has suffered similar symptoms and found the cure!

I have an intermittent fuel problem that seems unsolvable without cutting up the decks and removing the fuel tank (which we'd rather not do). The RIB is an 8m Cobra with a Yamaha 350hp 4-stroke.

Problem is that sometimes when cruising at mid range/high revs, the engine cuts down on revs and sometimes dies. Other times as the speed decreases, the engine comes back to life again. This seems to happen more in rougher seas., On occasions where the engine cuts completely, we have noticed that the primer bulb has been sucked flat suggesting a fuel blockage between the tank and the primer bulb. Engineer has checked fuel lines and replaced primer bulb, sea-trialed it for 40-mins and it didn't miss a beat. Next trip out - same problem!

My thinking is there could be something in the tank that is periodically blocking the outlet and then unblocking as the speed decreases and fuel moves around in the tank?

Could it be anything else that I haven't thought of?

Any advice welcome

Regards

Steve

matt h · 11 July 2016, 09:17

Def sounds like a blockage from the Primer Bulb to the Fuel tank.. might be worth changing the Primer bulb.. Also make sure the fuel tap is fully open as a process of elimination.

jeffstevens763@g · 11 July 2016, 09:54

if you have changed all external hoses and bulb is the pick up pipe plastic or rubber which could have perished but i would say you have something floating around Steve could be anything really any chance you could get a camera in to have a look you could hire one from HSS intrinsically safe. or its empty the tank and wash out, if the pick up pipe is removable then by emptying the fuel through it you might be lucky and pick the blockage up.
or siphon out through the filler large bore pipe but you would need to have the boat positioned so the fuel went to the pipe[might not be easy]

Dry Run · 11 July 2016, 10:09

Cheers guys

A camera is probably the next move after we've run it on a remote tank for a few trips. Problem is a 25l remote tank wont feed a 350 for very long

jeffstevens763@g · 11 July 2016, 10:45

Quote:

Originally Posted by Dry Run

Cheers guys

A camera is probably the next move after we've run it on a remote tank for a few trips. Problem is a 25l remote tank wont feed a 350 for very long

yep know that i had a ride on ribquest with twin 300 hp verardo's £140.00 20 mins

John Kennett · 11 July 2016, 11:01

I've had this a couple of times. Once it was a dodgy primer bulb, the other it turned out to be lumps of sealant which had been over enthusiastically applied to the fuel tank access hatch.

You've tried the primer bulb, so that suggests something in the tank. Do you have access to an inspection hatch? Is the fuel pickup accessible? As an interim fix, rather than draining the tank and cleaning out every last bit of silicone, a filter on the pickup worked for us.

Ribtec1 · 11 July 2016, 11:19

Hi
I had the same problem after i got my boat. The engine carried on exactly the same way as yours. I found that the fuel sender had dissolved ( through electrolysis )and debris entered the tank. My tank is stainless steel and has baffles so I am not sure that a camera will help. I ended up cutting a 4" hole in the deck and a small 1 in the tank. I was careful to fill the tank with water to avoid a possible explosion with all the fumes.
The fuel line is small with a bore of the inside of a biro so I can get blocked quite easily. It runs along the floor of the tank towards the stern of the boat. After cleaning the tank I resealed it and fitted one of those small inspection hatches. The biggest problem I had was getting information on the exact location of the tank so that I could drill in the right place.
Hope this helps

jeffstevens763@g · 11 July 2016, 12:48

if you can get the pick up out you could cut notches in it so the likely hood of all the notches sealing would be remote as a quick fix until you can sort properly

whiskylee · 11 July 2016, 18:08

We had a fuel tank vent hose full of water where it coiled under the deck, this caused us similar issues

Portholme · 11 July 2016, 18:41

i had the same problem with my Scorpion and it turned out to be old fuel that had turned to varnish and then flaked off. When i stripped it down there were flakes in the fuel pick up and right up to the water separator.

i replaced all fuel pipes and filters, emptied the tank and then cleaned it. it was not a fun job!

interestingly i think i have the same problem on my current boat as after an hour running i had the same symptoms, checked and the bulb was compressed. pulled the pick up and the filter was covered in what looked like wool. I wonder if my fuel tank air vent has been a hide away for insects! No flakes though, so very happy with that!

Dry Run · 12 July 2016, 08:40

Hi,

Thank you everyone for the suggestions. I think John's thoughts on silicon and Portholme saying about possible fuel contaminants could be spot on! Interestingly, Cobra agree with Ribtec1 about cutting a hole in the deck/tank and that's probably the route we'll go. Thanks to Whiskylee for the vent pipe suggestion, but we have run with the fuel cap off and the problem still persists, so I'm guessing it's not that.

I'll report back on what we find when the tank is drained/cleaned.

Thanks once again to everyone who posted.

Kind regards

Steve