300XS Soft Primer Bulb / Power Loss After High RPM Runs????

**wasvette** · 03-22-2017, 08:25 AM

Water tested yesterday 3/29; runs perfectly. Eliminating the anti-siphon valve and the trash in it solved hesitation,etc. Primer bulb has never gotten as hard as it does now in the ~ year we've owned the boat. Thanks to everyone for your input. Thanks S&F!
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Help - Please!! Hoping someone else here has run into this before. 2013 300XS with 400 hours; just had an extensive once over performed on the engine since it is new to us...new plugs, wires, fuel filter, good compression on all 6, new tracker valve, rebuilt pulse pump, fuel rail test good, digital pressure test, water pump, lower gear oil, etc, etc - all by a 40 year+ Merc tech. No issue first couple times out after this service.

Now, between Nov last year and today....

* Idle for long period (~ 4-5 min), stall ----- pump primer bulb; re-starts fine, runs fine.

* Run WOT (or close to it) 2 - 3 min, no problem; slow down to lower RPM, power loss, hesitation - turn off, pump primer bulb, runs great.

I'm assuming everything is good at the engine and that the issue is it is not getting fuel from tank? Again, there is no hesitation at high RPM.
What would cause the primer bulb to go soft at lower rpms? Could this be an issue at the engine? The fuel line (gray Merc) and primer bulb are new.

Would a 3 - 4 lb electric fuel pump be better in place of the primer bulb? I think this is what Wildman does on all the new Libs he builds. There seems to be
a split camp on this topic....some all for it, some adamantly opposed.

Any ideas would be greatly appreciated!! Very frustrating.

**RSWORDS** · 03-22-2017, 09:22 AM

Air leak. Try running it with a full portable tank hooked directly to the pulse pump inlet. This will tell you if your issue is on the boat side or the motor side.

Also, in the last few we have seen a HUGE increase in the number of pickup tubes that develop small hairline cracks and suck air in due to the ethonal gas.

**wasvette** · 03-22-2017, 09:31 AM

Originally Posted by RSWORDS

Air leak. Try running it with a full portable tank hooked directly to the pulse pump inlet. This will tell you if your issue is on the boat side or the motor side.

Also, in the last few we have seen a HUGE increase in the number of pickup tubes that develop small hairline cracks and suck air in due to the ethonal gas.

Great info; thank you! I will do this asap. The tank is probably original 1996 so anything is possible. Thanks for taking the time to reply!

**kct11** · 03-22-2017, 09:43 AM

There is no reason to have a primer bulb on there once the vst canister is full. Take it off and leave it on the boat for emergency. They are known to go bad.

**RSWORDS** · 03-22-2017, 10:10 AM

Yep, I would definitely check all fittings, lines, and pick up tubes. Just replace the tube if you pull it anyway.

**wasvette** · 03-22-2017, 10:46 AM

Thanks guys - I think I'm going to start with the pick up tube due to it's age and it's cheap - going to be a PITA to get the tank out where I can pull it out but gotta do it! If it's still persists I'll try the external tank test.

**XstreamVking** · 03-22-2017, 11:40 AM

There is a fuel connection in the rigging tube/hose that can develop a air leak on some motors. I remove it when I rig a motor since it is a bietch to get to. Also a oil line connection same place, I remove it too....

**wasvette** · 03-22-2017, 12:18 PM

Not sure if this could be it but this old anti-siphon valve appeared to have trash in it when I pulled it.

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I'll be replacing it and the fuel pick up.

**wasvette** · 03-22-2017, 12:20 PM

Originally Posted by XstreamVking

There is a fuel connection in the rigging tube/hose that can develop a air leak on some motors. I remove it when I rig a motor since it is a bietch to get to. Also a oil line connection same place, I remove it too....

Are you talking about in the black accordian rigging tube between the boat and the engine? If so, I've already replaced the fuel line and it's one continuous line from the primer bulb to the pulse pump inlet.

**XstreamVking** · 03-22-2017, 02:09 PM

Yes... Good thing to do, one pc hose less chance of problems. Anti siphon prob the culprit.

**RSWORDS** · 03-22-2017, 06:34 PM

Definitely get rid of it. But a restriction (like a clogged AS valve) on the tank side of the ball will pull the ball flat usually.

Originally Posted by wasvette

Not sure if this could be it but this old anti-siphon valve appeared to have trash in it when I pulled it.

I'll be replacing it and the fuel pick up.

**mjw930** · 03-22-2017, 09:36 PM

Originally Posted by XstreamVking

There is a fuel connection in the rigging tube/hose that can develop a air leak on some motors. I remove it when I rig a motor since it is a bietch to get to. Also a oil line connection same place, I remove it too....

I spent time today rigging my new 300XS and to say the way they make that connection part way down the rigging tube is insane. I fought with it and got it done but I'm not happy with the way it fits so I'm pulling it apart tomorrow or Friday and running the oil and fuel lines directly to the motor to eliminate that midstream connection. It will also allow me to properly dress the wires, hoses and cables within the tube. Call me anal but that's why I'm rigging my new boat and not someone else.

I've rigged dozens of high performance boats over the years but this is my first outboard so I figured I'd go with the way Mercury designed it but they really screwed up on this design.

**wasvette** · 03-23-2017, 07:27 AM

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So I'm guessing this older (circa 1996?) metal fuel tank has a permanently welded in fuel pick up tube? Is this common on older tanks? I purchased a new Moeller with the plastic pick up before I pulled the fitting on the tank (IMG 1461) but can't use it. As you can see in 1461 nothing was attached to the fitting when I removed it.

I also punched out the ball bearing in the anti-siphon valve per my mechanic. He said it's not necessary on this outboard set up. So with $5.00 in thread sealant and existing parts, I'll be putting it all back together and water testing.
I'm optimistic (always love that word) that the trash in the check valve was the issue.
Thanks to all for the help & thanks to Scream and Fly!

**RSWORDS** · 03-23-2017, 01:04 PM

I'd take a portable tank with you just in case you need to do more troubleshooting.

**WILDMAN** · 03-23-2017, 06:45 PM

I have always run one piece lines and hoses without the splices. It's much easier.

Originally Posted by mjw930

I spent time today rigging my new 300XS and to say the way they make that connection part way down the rigging tube is insane. I fought with it and got it done but I'm not happy with the way it fits so I'm pulling it apart tomorrow or Friday and running the oil and fuel lines directly to the motor to eliminate that midstream connection. It will also allow me to properly dress the wires, hoses and cables within the tube. Call me anal but that's why I'm rigging my new boat and not someone else.

I've rigged dozens of high performance boats over the years but this is my first outboard so I figured I'd go with the way Mercury designed it but they really screwed up on this design.