The mystery Continues, any Ideas?

[gman2560]

Pardon the explanation as i wish to be thorough.

1977 Mercruiser Inline 6 250 Cu engine....
When running the boat, it will run fine for 30 or more minutes. All the sudden it will lurch (best description i have) a few times like it lost power and then stall. The engine starts right back up like nothing is wrong. Once it starts doing it, it will continue to act up like that. I can run at no wake back to the marina and it may only lurch and stall once or it may not, but any faster and its an issue.
First things first...replaced both fuel filters one at the pump and one at the carb. Still did it.
Siphoned remaining gas from tank (in case of contamination), Replaced the fuel pump, anti-siphon valve, and fuel line between pump and carb. Still did it.
The distributor is new and yesterday a mechanic removed and inspected the carb and said it was clean and good.
We have replaced the coil with a known good coil and intend to test it tomorrow. The mechanic speculated that perhaps the coil was marginal once it got hot causing lack of spark under a load.

Any ideas??? thanks!

 

[whywhyzed]

Re: The mystery Continues, any Ideas?

how soon after any work or parts replacement did this issue begin? Did it start with a small lurch and get worse? Or consistently the same lurch since the first time it did it?

ideas:
-faulty shift interrupter switch or wiring touching or grounding on something.
-key switch or wiring under the dash
-wiring or connector anywhere from dash to coil

sounds like your mechanic is a parts changer....

need someone handy with a multimeter to check power at the coil while you cruise around.... see if the Voltage drops when it stutters....

 

[Haut Medoc]

Re: The mystery Continues, any Ideas?

You did not mention pulling & looking at the fuel pickup tube & screen.....
Did you do that?.....
If I were to drain a tank, that is where I would do it from.....
With the boat at a suitable angle so that I might pump out everylast drop & whatever crap there is......
As far as it could be an electrical problem, you could pull the plug where the harnesses meet apart & make sure they are corrosion free....
Perform a 'wiggle test' on all electrical connections.....
Bring a DVM & a fuel pressure test gauge & the means to hook it up with you next time.....
I'm still leaning towards crap in your pick up......​

 

[Windykid]

Re: The mystery Continues, any Ideas?

Is there an inline filter in the carb?