3.0 Mercruiser

[Tavinthor06]

Yes I tried that no pressure when opening the cap and same issue while cap is off.

 

[airshot]

Try adding a squeeze ball in the fuel line like they use on outboard motors. When it acts up, check the ball, if not collapsed pumpnit and see ir the engine comes back to life. If it does, you have a pickup or pump issue.

 

[Scott06]

Spark is on point, no issue there, I know it's a fuel issue all lines are cleared no clogs no pressure build up in the tank. Just not figuring out why it'll run so amazing for over an hour then just suddenly die. Aside from taking the carburetor apart or the fuel pump I'm not seeming to figure it out

Well if you made this much improvement by cleaning the tank and lines would think taking the carb apart for cleaning would be worth knocking off the list. The anitsiphon valve might be worth pullling to see if it hangs up intermittently, are the inside of the hoses degraded ?

 

[Tavinthor06]

The hoses were replaced two years ago with Trident hoses and look very good no sign of issue there. Think it's time to take the carburetor apart to see if there's gunk in the accelerator pump or if the float is sticking.

 

[airshot]

When hises fail it is from the inside even with the outside looking great. My own fuel line was just replaced less than 3 years back, but after my inspection before retiring the boat for the winter, I removed a couple fittings and found the inside of the fuel line beginning to come apart. Ordered a new one for next season.

 

[Tavinthor06]

Changed the mechanical fuel pump, took it out and it ran absolutely amazing for almost three hours then died on me again, could start it right up but as soon as I'd put it into gear and gave it fuel it would die. Put carb cleaner in the carb got it fired up and it trash amazing again so took it into dock without issue about 40 minute ride. Still puzzled as to what's causing this. Guess it's time to strip the carb and give it an overhaul.

 

[QBhoy]

Hi. As long as your filter in at the mechanical fuel pump is clean, the insert filter you might have at the fuel pipe fitting going onto the carb too (don’t think you’ve mentioned this, if she has one that is) and your pick up and check valve aren’t getting clogged (sounds like it to me), then you need to take the carb off again. Thoroughly clean it. Ever last and tiniest part. Make sure in particular that the float valve mechanism and needle are as they should be

 

[bbook83]

I see you mentioned you ”cleaned the tank”, but without removal, it is difficult to confirm you have all debris removed. The pickup tube can still periodically plug with debris, which then drops off as the suction reduces. You had two suggestions to run on a remote tank to isolate the problem. I don’t see where you say you did that. It is easily done and well worth doing.

 

[Simoniz]

I see you mentioned you ”cleaned the tank”, but without removal, it is difficult to confirm you have all debris removed. The pickup tube can still periodically plug with debris, which then drops off as the suction reduces. You had two suggestions to run on a remote tank to isolate the problem. I don’t see where you say you did that. It is easily done and well worth doing.

I once had a car which did exactly as your boat is doing. After trying all sorts, I eventually arrived at the fuel tank pick up, and the pick up pipe, which was positioned too close to the bottom of the tank, with end being cut at an angle such that the end of the pipe would suck itself flat onto the wall of the tank, thus creating a near perfect seal.
Had the pipe been cut off straight, or mounted further from the bottom of the tank, it would not have been able to do so. I simply bent the pipe slightly, so that it could no longer touch onto the tank inner wall, and it was fine.
Long story short - I reckon you might have a similar issue here, or debris floating about which periodically blocks the pipe. Try a remote tank.