fuel tank issues

[9325luhrs]

93 luhrs 25 with twin Merc. vortex 5.7 late 90's inboards.

While accelerating one engine will not exceed 3000 rpm. It will cruse fine at 3000 rpm.

I have isolated the problem to be in the port fuel tank, by supplying fuel direct from each tank to each motor and then switching lines at the tank. Some of the other items that have been replaced or checked are, filters, pumps, anti-siphon valves, fuel lines, ball valves, cylinder compression, timing, etc?

Do fuel pick ups have any type of filter or strain? And how do you access it?

 

[Bondo]

Re: fuel tank issues

Do fuel pick ups have any type of filter or strain? And how do you access it?

Ayuh,.......... Usually........

Unscrewing the outlet elbow will usually bring the pick up tube with it.......

 

[Haut Medoc]

Re: fuel tank issues

Generally, yes they do & there is usually a deck access fitting......
One more thing to check is the tank vent.....
Welcome to iboats, btw......​

 

[Haut Medoc]

Re: fuel tank issues


Quote:
Originally Posted by Don S
Here is a list of possible causes of low WOT. Mark them off as they are actually checked and actually do the tests and you will find your problem.

Engine Won't Reach Operating RPM. Check

• Fuel condition. Type and Octane possibly old fuel
• Propeller pitch or diameter, damaged blades
• Restricted fuel pickup tube or anti siphon valve Fuel System Test
• Crankcase oil volume, high oil level can cause aerated oil and lifter collapse
• Marine growth on hull and outdrive
• Wrong gear ratio in outdrive
• Restricted carburetor air intake (clogged flame arrestor)
• Restricted exhaust system (broken exhaust shutters/flappers) in engine transom shield or drive
• Poor cylinder compression Compression Test
• Carburetor defective, or wrong type.
• Fuel pump pressure and vacuum
• Boat overloaded, improperly loaded, or improperly trimmed.
• Engine Overheating
• Engine timing and ignition system operation
• Remote control cables and linkage for proper travel to open throttle plates fully.

__________________
Here's the rest of the checklist.......

 

[9325luhrs]

Re: fuel tank issues

Quote:
Originally Posted by Don S
Here is a list of possible causes of low WOT. Mark them off as they are actually checked and actually do the tests and you will find your problem.

Engine Won't Reach Operating RPM. Check

• Fuel condition. Type and Octane possibly old fuel all fuel was replaced
• Propeller pitch or diameter, damaged blades just taken out of the water, painted and checked both props closely.
• Restricted fuel pickup tube or anti siphon valvereplaced both lines, and changed the valve. Fuel System Test
• Crankcase oil volume, high oil level can cause aerated oil and lifter collapse oil checked after every run and changed ever 25hours
• Marine growth on hull and outdrivejust painted and no out drive
• Wrong gear ratio in outdrive i don't think luhrs would put the wrong trans in the boat, but maybe
• Restricted carburetor air intake (clogged flame arrestor) carbs just rebuilt
• Restricted exhaust system (broken exhaust shutters/flappers) in engine transom shield or driveproblem moves when fuel lines are switched
• Poor cylinder compression Compression Testmotors just removed and all compressions test were preformed by a trust worthy mechanic
• Carburetor defective, or wrong type.again problems moves when you switch fuel lines
• Fuel pump pressure and vacuumread above
• Boat overloaded, improperly loaded, or improperly trimmed.boat is empty besides gas, fresh water two engines and trans
• Engine Overheatingi think i would notice that on the the gauges since they were just replaced and seem to be working fine according to a temp gun
• Engine timing and ignition system operationjust switched to electronic ingnition and both idle and advanced timeing has been set.
• Remote control cables and linkage for proper travel to open throttle plates fully.

agian read above

__________________
Here's the rest of the checklist.......

read the question before answering.

 

[9325luhrs]

Re: fuel tank issues

Generally, yes they do & there is usually a deck access fitting......
One more thing to check is the tank vent.....
Welcome to iboats, btw......​

Thank you for the vent idea. hadn't thought of that. but it seems to be working fine. pulled the vent off the tank and was able to blow both ways very easy.

the pick up tube can't be removed since it is welded to the inside of the tank. there is no strainer or filter within the pick up tube. i have replaced all items in line from tank to engine. i think it is time to drill out the pick up tube and put in a new one. unless anyone else has any thoughts.

 

[Bondo]

Re: fuel tank issues

problem moves when fuel lines are switched

Ayuh,........

I guess you've Found the right neighborhood,......

Now you've got to figure out Why you can't get the fuel From that tank.......

 

[farmboy]

Re: fuel tank issues

Assuming the problem existed before all the new equipment was installed, but is the anti-siphon device flow in the correct direction? Can you move compressed air through the fuel pick-up back into the tank? Is it possible to rout the pick-up tube with a rod? I think an old shift cable might work for the task due to its flexibility.

 

[flabum]

Re: fuel tank issues

Sometimes there are spare pickups in the tank, do you have any spare pickups?

Drilling out the old pickup tube can be exremely dangerous. If you are sure it is the pickup, remove the tank and clean it out real well. I use Joy dish washing soap. Then leave the tank full of water. Then you can attempt to do the repair safely.

If you have a welding shop nearby, for $20, they can weld in a new bung for you (leave the old one in and cap it) and you can screw in a new pickup tube.