engine bogs down

[douginmn]

I have an older ( mid 1970s) Mercruiser 165 inline 6 cyl. when I first take it out, it runs great (for the first hour) If I putt around the lake for an hour or more at low RPMs and then try to go fast, it struggles to get up to speed (in fact, it will not get up to speed) when I give it more throttle, it wants to cut out. I don't know if it is a fuel problem or an electrical issue. could someone please give me a starting point? much appreciated, Doug.

 

[Lwarden]

Re: engine bogs down

I have an older ( mid 1970s) Mercruiser 165 inline 6 cyl. when I first take it out, it runs great (for the first hour) If I putt around the lake for an hour or more at low RPMs and then try to go fast, it struggles to get up to speed (in fact, it will not get up to speed) when I give it more throttle, it wants to cut out. I don't know if it is a fuel problem or an electrical issue. could someone please give me a starting point? much appreciated, Doug.

sounds like the fuel pump to me but Id start by cleaning all the filters/water fuel separator. And check to see if there's a filter at the carburetor housing too. Mine was doing the same thing even though it is a V8 it ended up being the fuel pump.

 

[Silly Seville]

Re: engine bogs down

Sounds electrical to me. Heat builds up, resistance increases, lack of spark to plugs...bingo, no power!

When was your last tune up? There are many points of contact/resistance in the ignition system. Battery faulty, ground faults, coil, wires, plugs, distributor cap, points, rotor, condenser. Did I miss anything?

 

[BarryF]

Re: engine bogs down

sounds like the fuel pump to me but Id start by cleaning all the filters/water fuel separator. And check to see if there's a filter at the carburetor housing too. Mine was doing the same thing even though it is a V8 it ended up being the fuel pump.

I am having the same symptoms with my '94 Stingray with 3.0l Mercruiser. [Let me know if I should start a separate thread]
I changed the plugs, cleaned the flame arrestor (was VERY clogged), 'cleaned' the carb (simply sprayed carb cleaner while running), treated fuel with Seafoam with no improvement.

Next step is to check the fuel filter(s) and check fuel vent for blockage (read in another thread that it could be vacuum lock). Will also check the fuel pump.

Now the newbie questions:
Where is/are the fuel filter(s)? Not sure if I have a water fuel separator.
How do you diagnose the fuel pump?
Are there diagrams for the Mercruiser 3.0l to help identify the parts?

Thanks in advance for helpful tips. Again, let me know if I should start another thread. The symptoms matched exactly so I thought it would help to keep them together.

Barry

 

[generator12]

Re: engine bogs down

One step you could take is to tee a gauge off the line between the fuel pump and the carb. Should stay somewhere between 5 and 7PSI. It would be interesting to see if the pressure drops off between the point where it's running well and failing.

 

[douginmn]

Re: engine bogs down

hey thanks for the advice, I have the new points, condenser and rotor. Also, have you ever heard of the coil getting too hot and not throwing a good spark? someone told me that but I'm not sure if it's true. thanks again, Doug

 

[Silly Seville]

Re: engine bogs down

...have you ever heard of the coil getting too hot and not throwing a good spark? someone told me that but I'm not sure if it's true

YES YES YES!

If the coil is too hot to hold, you have problems. That is a symptom of windings breaking down and generating too much resistance. Thus the lack of required spark energy for the engine to perform well at high rpm, where the greatest electrical charge is necessary.