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 Mercruiser 7.4L PT Bravo III wont stay above idle.
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Author Previous Topic: Buying 1993 Ventura 9.8 Topic Next Topic: Free Dock  Mat for 4080/3880 Owner in NC Area  


RO# 30614

Posted - Sep 07 2009 :  21:38:18  Show Profile  Reply with Quote

Just hand pumped out 60 Gallons of 2 year old fuel, then changed the oil. then put in 6 Gallons of good gas and started her up after non using for 3-4 months. Started her on the trailer on land with a hose. Idles fine after a few minutes I tried to rev higher gradually and it starts to idle unevenly then (while keep ramping the throttle up) I hear what sounds like a swooshing air sound and then it starts to slow down and sputter. If I quickly ramp down (back to idle) it recovers, and idles nicely... Then ramping it up again, it runs a bit faster maybe 1200-1500 RPM then giver her more gas and swooshing and then same thing -sputter like it's going to sputter and quit and it does if I just leave it there...

So I, turned it off, took the flame arrester off and notice a bit of white powdery mold in the vanes and on some hoses. So I cleaned it... And I sprayed Starting fluid in the the edelbrock carb and cleaned it a bit. Put it all back together and started her up This time if runs better... It will rev up 3000-3600 but wont hold any RPMS above say 1500 without sputtering, slowing down and then quitting. If I listen for the swoosh air sound when giving it throttle and keep it right where that swoosh comes on, it will rev up (like I'm pumping the gas) to 3000 and then back down to 1500 then up to 2700 for 5 seconds then down then 1300 for 3 seconds then Up to 2500 for 4 seconds etc... but I'm not moving the throttle.

So it wont keep a steady RPM and seems that goosing it revs it up but floods it.

Anyone with experience want to weigh in on possible things it could be?

Previous owner was an engineer and put in 2 fuel oil separators with fuel cut off valves all over the place, and I've worried since I bought it that that would restrict fuel flow... But I don't have any experience with Mercruiser engines or running off the hose... Please weigh in with any info/ideas! The boat is new to me!

P.S. yes I know I shouldn't be going above idle on the hose but I'm watching the temp gauge, and main thing I don't want to launch & find out all I can do is idle. So I'm testing it to see if I can hold a RPM for 10 seconds or so... Thanks for any info!

Homeport: Jupiter FL


RO# 9068

Posted - Apr 15 2011 :  11:06:55  Show Profile  Reply with Quote
Time to rebuild the carb. When it sits for that long the gas turns to slug in the carb. It may seem to be fine but not where the eye can't see.

Homeport: Rock Hill CT Go to Top of Page
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