Fuel system problem on 13 yo storage boat

[Moonstruck]

Resurrecting the 2000 3L 135hp engine. The boat was in storage for 13 years. The engine is running. Took it out for a test. When attempting to get on plane, or succesful plane run, after 30 to 90 seconds the engine looses power. It acts just like the throttle was pulled back. It usually keeps running at idle, but rough. It will smooth out and be ready for another pull after about 15 seconds. The amount of time it takes to loose power varies. It runs well and normal at idle or low speed maneuvering. I suspect a fuel delivery problem. Fuel filters were changed during the original rehab. I think the float bowl is not filling fast enough to keep up with a high fuel demand condition. The question is why.

What I plan:
1. Open fuel tank and inspect tank, fuel pick up, and fuel lines from tank to pump.
2. Recheck fuel filters.
3. Check for clear fuel line from pump to carburetor.
4. Check fuel flow from the mechanical pump.
5. If the above does not solve problem, rebuild carburetor.

How do I check fuel pump output? I was thinking of clamping a rubber line from the fuel line that feeds the carb, cranking the engine, and seeing how much fuel it delivers over 10 seconds. Is that the correct procedure? How much fuel should it put out? My recollection about these mechanical GM pumps in cars was that usually the diaphragm failed and leaked fuel out the weep hole, but they usually kept the engine running unless it really let loose. No fuel detected in the weep hole hose that runs back to the carb. Any other way to test the pump?
Any other thoughts or advice appreciated. Ty.

 

[Scott Danforth]

Clean the anti-siphon valve
Check the fuel pickup filter

Test fuel pressure with a pressure gauge (get the Mercruiser test fitting)

After 2 years any fuel turned to goo

After 13 years the goo would have dried to crusty bits

You added fresh fuel which now has those crusty bits plugging your carb, fuel filter, anti-siphon valve, etc

You need to clean. The whole fuel system

 

[flashback]

I'd say your list is a good one..13 years of old fuel would cause problems...

 

[Moonstruck]

The fuel tank was drained as much as a siphon could drain it. Fresh fuel added. Where, and what is the anti-siphon valve? The fuel pump is a mechanical pump, not electric. It will only pump in pulses when the engine turns to fill the float bowl. I would think there is a spec on volume/time fuel pumped. Is there a pressure spec on a mechanical pump?

 

[Scott Danforth]

The anti-siphon valve is the fitting at the fuel pickup tube the fuel line is connected to

Did you pull the sender to inspect the inside of the tank?

 

[Moonstruck]

The sender was pulled to siphon the old gas. Not much in there. It was drained down to close to empty when it was put up. What there was had what looked like some kind of algae growing in it and it stunk bad. It was siphoned and suctioned a bit. I will re-inspect the tank and anti siphon valve and lines with this new information.

 

[bbook83]

The following process helped me solve a similar problem: Run the engine under load on a remote fuel tank, which could be as simple as pulling the fuel line from the anti siphon valve barb and putting it in a half empty 5 gallon gas can of fresh gas. If you cannot do it that
way safely, use an outboard type remote tank. If the problems continue with that setup, your problem is downstream from the tank. If the remote tank setup eliminates the problem, or at least improves how the engine runs, look at the pickup fittings and tube and anti siphon valve. You can buy an endoscopic camera for $20 on Amazon, which can be inserted through the fuel gauge sender opening of the empty tank to see what foreign materials may be there that can be sucked out. After that, put a small amount of fresh gas in the tank and run it under load. If it starves of fuel, use the camera through the sender opening without submersing it, and see if you can determine if there is an obstruction from debris at the pickup.

 

[Moonstruck]

I will be removing the fuel pick up tube and anti-siphon valve for inspection and replacement if necessary. Is there supposed to be a screen or something similar in the end of the pickup tube as a strainer? When I put it back together, what should I use as thread sealant? I have some multi-purpose thread sealant that is rated for brass, aluminum, gasoline, and a long list of other things. Is this good or should I be using something else?

 

[kenny nunez]

There might be a fine screen filter inside the tube, be sure to remove and pitch it.

 

[bbook83]

I agree with Kenny as to the screen inside the pick up tube. A quick internet search will reveal hundreds of opinions as to using sealant on fuel fittings. The anti siphon valve into the pickup tube is an NPT thread, as is the pickup tube into the tank. In my humble opinion, no sealant is necessary.

 

[Moonstruck]

I took apart the anti-siphon valve and dip tube. The ball in the valve was stuck in a partially open but mostly closed position. A hard push with a paperclip, carb cleaner, and compressed air, it was functioning normal. Everything was put back together and tested on the lake. The engine runs well at all power settings. Tough little engine for all it has been through.

Thank you to everyone who had input on this and helped me figure it out. Happy boating!