50 HP MERC holds top RPM about 10 seconds - then idle speed

[jjkos]

50 HP MERC holds top RPM about 10 seconds - then idle speed, outboard is about 15 years old. bulb on fuel supply line was completely sucked in when running. So I thought that was the problem, changed out the bulb with a new one. And now the Motor still does this. IT doesn't die out it just goes to idle speed no matter when the throttle is placed. After I wait a minute or two it will go back to full throttle, then it dies out again. I have tried to run it with the fuel cap open and it doesn't help. After I installed the new bulb It seems the problem got worse and it runs even shorter. Thank you for any advice! It a short season where I live and I would love to get a few more weeks in!

 

[Chris1956]

You have a restriction between the primer bulb and the fuel tank. Since you opened the fuel tank cap, it is not the vent. If it is a built-in tank, I would suspect the anti-siphon valve. The sometimes have filters on that that clog.

if portable tank, I would suspect the fuel pickup screen.

 

[jjkos]

Great! Thanks Chris! its a built in tank, any idea where tge anti-siphon valve is located? Is it usually next to opening where you would refuel?

 

[Chris1956]

The antisiphon valve usually (usually) screws into the fuel pickup tube elbow. I would remove the fuel pickup tube and inspect the fuel screen on the end. Then I would unscrew the A-S valve and see what is what.

On another note, my old SeaRay had the A-S valve in the fuel pickup tube itself. It had a filter that could clog. The fuel pickup tube that went into the tank, unscrewed from the elbow to expose the A-S valve and that pesky filter.

 

[jjkos]

ok I will check it all out this weekend, Thanks Chris

 

[jjkos]

Here is what is on top of my fuel tank, I removed fuel supply line, but I was not able to unscrew this part. it was stuck in place and would not budge at all. Any suggestions on how to safely remove this valve without breaking it. ?

 

[Chris1956]

Tricks to remove that fitting? Spray it with penetrating oil. Remember to put a wrench on both the tank hex fitting and the elbow. That's about it. You do not want to break that fitting. Is it aluminum? Tank is steel or aluminum?

Steel and aluminum tanks are quite old by now. any chance of replacing it with a new tank?

I would first try a portable tank and see if fixes your problem. If so, the installed fuel tank is likely the culprit, and you need to remove that fitting.

 

[jjkos]

brilliant! great Ideas. I have a portable I will try, never thought of that!! The tank is a plastic tank.

 

[bwkre]

I suggest you thread a fitting into that street elbow before trying to remove it. It doesn't have to be real tight, just in there. It will prevent distortion of the female threads in the elbow when you crank on it to remove it Important if you plan to reuse it. If it's stainless, put a bit of oil on the threads to lubricate them, less chance of damage to the threads.

 

[Texasmark]

If you have been using ethanol, you could have clogging in your fuel line between the tank and the engine. At 10 years of age, I had tan crud in chunks that followed the contour of the hose plus small pieces clog my squeeze bulb and accumulate at the fitting at the engine....the hose was Quicksilver OEM gray, appeared to be silicon and the inside of it didn't appear to be degraded. The crud had to come from somewhere and that was my first engine to ever have that kind of a problem and the first engine to run ethanol. Go figure!