2012 3.0L TKS runs great with muffs, but slow on lake...

[ESGWheel]

The pressure showing on the inline gauge did drop as the throttle was increased. It was idling at like 4.5 PSI, then at double the throttle, the PSI went down to 4.2 PSI closer to 3000 RPM.

Were you underway or on the muffs for those readings?

 

[Lou C]

Someone here mentioned that I would have to take the exhaust manifold off then (replace the gasket) to check to see if the flapper was in place. When you say, "missing and blocking the exhaust", do you mean that it might have overheated, crumbled, fallen down the exhaust and it remains are now blocking out drive? The videos that I've seen, this flapper looks like a rubber butterfly that barely touches the exhaust. either round or oval shape. I've attached a picture of my exhaust where the flapper might be. The large U-shape piece is cast iron, then a rubber boot, then back to cast iron. Would I be taking off the rubber boot only, or the entire pipe to check? I do have a video borescope with a 15' cable if I can find a place to insert it. Thanks...

What you can try is to spray the part of the down pipe (below the rubber hose) with silicone, loosen the clamps and spray silicone in the joint between the hose and the exhaust elbow (top curved U shape piece of cast iron) and the hose. Let soak in for a bit. Then try the move the hose up and down, side to side, and slide it down onto the down pipe. Then you should be able to see the exhaust flapper and inspect it for free movement. If it's there and moving freely exhaust restriction is not likely your problem. If it's not then you got more work to do, let us know what you find if you do investigate this....

 

[Lou C]

The pressure showing on the inline gauge did drop as the throttle was increased. It was idling at like 4.5 PSI, then at double the throttle, the PSI went down to 4.2 PSI closer to 3000 RPM.
Anti-Siphon Valve - What am I checking for here? Blockage, if the check ball is missing? Thanks.

two things, the anti-siphon valve can be gummed up with crud inside, the ball can corrode in place but also the part that it screws into (the dip tube or withdrawal tube as it's called) can have a screen on the bottom that can be blocked by crud also.
You can rule these out without taking anything apart by running the boat on an outboard fuel tank. That eliminates the boat fuel tank as a potential problem and leaves you with fuel pump/carb exhaust restriction to check.
If you do be careful, I have a set up to do this with a 6 gallon outboard tank, I put a short length of hose after the barb and added a shut off valve, just in case the fuel line to the fuel filter ever leaks! Also be sure to plug the fuel line coming from the boat's gas tank to make sure no fuel spills in the bilge.

 

[GeorgioP07]

The pressure showing on the inline gauge did drop as the throttle was increased. It was idling at like 4.5 PSI, then at double the throttle, the PSI went down to 4.2 PSI closer to 3000 RPM.
Anti-Siphon Valve - What am I checking for here, the valve with the green marker line on it? Checking it for any blockage, clean it out, verify that check ball is in place? Thanks.

 

[GeorgioP07]

Were you underway or on the muffs for those readings?

This was all performed while the engine was running on muffs in the garage. As for getting out on the lake, I might, have one weekend left, sadly.....the temps are getting into the 50's now, and getting close to winterizing the engine either way.

 

[Lou C]

Yes to the question on the anti siphon valve. The ball must move freely and not stick. Be careful removing it. Look inside the hole in the fitting (top part of the fuel pick up tube) it's screwed into, do you see crud in there? If so it should be removed from the tank and cleaned out or replaced. Both the fuel pick up tube and the anti siphon valve have pipe threads, that should get a bit of fuel resistant sealant when reinstalling.

 

[GeorgioP07]

try the move the hose up and down, side to side, and slide it down onto the down pipe. Then you should be able to see the exhaust flapper and inspect it for free movement. If it's there and moving freely exhaust restriction is not likely your problem.

Alright Lou, Thank you. I will let the boot area soak in silicone spray overnight. Even if I can get a 10mm opening between the rubber boot and the cast iron, I can slip my boroscope camera down there and check out the flapper. Thanks.

 

[Lou C]

Here's one on my V6 4.3 Cobra. middle pic is new
top & bottom is burned up from overheat
had to pull the outdrive to get all the bits out lol.
This an OMC but Mercru is similar...

 

[Bondo]

What you can try is to spray the part of the down pipe (below the rubber hose) with silicone, loosen the clamps and spray silicone in the joint between the hose and the exhaust elbow (top curved U shape piece of cast iron) and the hose. Let soak in for a bit. Then try the move the hose up and down, side to side, and slide it down onto the down pipe. Then you should be able to see the exhaust flapper and inspect it for free movement. If it's there and moving freely exhaust restriction is not likely your problem. If it's not then you got more work to do, let us know what you find if you do investigate this....

Ayuh,...... Instead of silicone, use Quicksilver Power Tune,.....
It makes rubber slicker than snot,.....

 

[GeorgioP07]

Good news is that the flapper is 100% intact.
I was able to open the rubber coupler enough to look down inside and see it. As to how pliable it is , - I put a blank arrow down there and one of the rubber flaps moved, so I think that it is pliable enough.
Bad news is that the anti-siphon valve snapped off and left about 4 threads into the elbow that comes out of the gas tank. No sign of the check ball and spring unless they went flying, or are still stuck in there.
It seems to be one of the aluminum ones that you are supposed to avoid, but it was in there already, and I think, a bit corroded (dielectric, galvanic corrosion) with the steel elbow.
I tried to loosen the elbow and it's pretty snug. Do you have any ideas as to how to remove that, replace it, or what that part is called? Thanks...

 

[Lou C]

That’s the fuel pick up tube also called the fuel withdrawal tube. Use penetrating oil, time & patience. Do not force it work it back & forth just a bit spray more penetrating oil, get it to move a bit more etc. Dang aluminum!