3.0L OMC High RPM sputtering

[sweaver76]

Hey all, I've been doing some research on this site, but have not been able to identify my problem yet. <br />3.0L OMC Cobra stern drive, 140HP. <br />Engine runs fine in neutral. <br />In drive, boat runs good from idle to about 3000RPM. Can hold 3000RPM continuously.<br />However, from 3000 to WOT (about 4200) it will run strong for about 10-20 seconds, then sputter and surge and usually stall, unless i reduce throttle. If I save it from stalling, and go back to full throttle, the cycle will repeat itself. It will not run at WOT for more than 30 seconds, usually closer to 10 seconds. But it always gets up to at least 4000 RPM or so before it begins to die again, even if i go from a near stall, right back to full throttle.<br />I have replaced plugs, Fuel filter/water separator, cleaned air intake on top of carb (flame arrestor?). Any ideas as to where I should be looking next? Thanks

 

[waterone1@aol.com]

Re: 3.0L OMC High RPM sputtering

I think it is definetly a fuel issue. The easiest thing to check for first would be a partially obstructed gas tank vent line. Remove or loosen the gas cap and try running it. Next thought would be to check all gas lines and hose clamps for tightness, any leak before the fuel pump would cause loss of fuel pressure or air to be in the line. The screen on the end of the gas tank pickup line could be partially blocked. You would have to consult a manual, but some carbs have a filter built-in to the fuel inlet, if equipped that filter could be clogged. In my opinion, what is happening, as the engine needs more gas (at full throttle)something is causing a disruption and the float bowl level is dropping.

 

[SeaSkwurrel]

Re: 3.0L OMC High RPM sputtering

Just a thought-possibly a low float level could do this? Or bad power piston/valve?

 

[sweaver76]

Re: 3.0L OMC High RPM sputtering

Thanks for the inputs! I am not real familiar with gasoline engines. I can do some basic stuff. But I am more familiar with aircraft engines (jets). So i can learn pretty quick.<br />I appreciate the help, but you may get a stupid question here and there.<br />I checked for leaks...none found, also opened he fuel cap...no difference. I am about to check the filters, but got a couple questions. From the filter/seperator, the fuel line goes to the pump then a metal line up to the carb (also a clear rubber tube...looks like air though). Where would the filter be?<br />Unfortunately, I don't think a manual is possible...nobody's even heard of "tiberias boats" before. Not even Google!<br />Lastly, waterone, is the float bowl just a reserve of fuel in the carb for acceleration? So you would be suggesting that at full throttle, the engine is using more fuel than it can replace into the carb because of a blocked fuel line? If so, shouldn't I be able to remove the flame arrestor on the carb after just idleing or low rpm cruising and see if there is fuel in the bowl, then run it at WOT, let it sputter and stall and see if fuel is still in there? If no fuel in the float bowl after the stall/sputter, wouldn't that confirm my issue is a fuel issue?<br />THANKS SO MUCH!! the marina says 3 weeks to turn it around....i'd rather not lose all of july and part of august without it!