Mercruiser 3.0 loss of power

[Farina]

Hello, I have an older 3.0, it's a little hard to start, once I get going it runs fine after 20 minutes or so you bring it back to idle and full engine warm up it will not go back to full power, only 2500 rpm, the anti syphon valve was removed by the former owner and I replaced the pick up tube. Any ideas

 

[tpenfield]

Welcome to iBoats. . .

For the best responses it is always good to post the serial number of your engine, if you have it handy.

 

[Scott06]

Sounds like previous owner and yourself have been tracking down and a fuel supply issue?

So symptoms are -
hard to start , then runs ok ( gets up to 4500 rpms or so ?)
After 20 minutes of normal running (at speed under load) then you cannot get over 2500 rpm under load?

If that's the case first thing I would try is opening the fuel tank cap to see if the vent is plugged and under vacuum.

Have you measured the fuel pressure while running?
Also start with some basics - compression check (prob ok it it runs well at times), check of ignition components (good spark - check with cheap spark gap tester? cap and rotor plugs etc ok?) and check ignition timing- both initial and total advance.

What does fuel filter in bowl of fuel pump look like? water debris?

If you have an older points distributor with advance weights could be hanging up the advance mechanism

 

[Farina]

Thanks for replying, update, I disconnected the fuel line from the tank , nofuel was in the line, I connected a fuel line with a external tank and a squeeze bowl. Started up and idle was very high, it just started to rain so I shut it down, I am thinking maybe a fuel pump? Your opinion
Thanks

 

[Scott06]

Thanks for replying, update, I disconnected the fuel line from the tank , nofuel was in the line, I connected a fuel line with a external tank and a squeeze bowl. Started up and idle was very high, it just started to rain so I shut it down, I am thinking maybe a fuel pump? Your opinion
Thanks

Could be fuel pump, could be blocked pick up, could be clogged fuel filter in pump, could be clogged fuel tank vent , Could be clogged fuel line , air leak on suction side of pump....Basically work back carb to pump to tank and see where you aren't getting gas before you throw parts at it.

If I were a betting man I would think you probably got junk in your fuel tank and lines, probably have to take them apart clean them, replace any degraded rubber hose etc, then probably clean out your carb... but hard to tell until you look into it.

 

[Farina]

Thanks for all input, problem solved, bad fuel line