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Engine trouble

6K views 19 replies 7 participants last post by  Blu 
QUOTE(Blu @ Aug 14 2009, 04:26 PM) <{POST_SNAPBACK}>Hi,

I'm having trouble tracking down an engine issue. Boat is a 1986 Sea Ray with a 5.0L 230HP mercruiser engine.

The problem is that the boat will only run above 3000 RPM for about 10 seconds before it starts to hesitate and buck. I don't hear an electrical miss. Watching the tach - I will see it drop several hundred RPM and then bounce back up and all over until I drop the throttle back and get it under about 3000 RPM. The water seperater/fuel filter only has about 20 hours on it. The in-lin fuel filter is brand new and the cap/rotor/wires/plugs all look like new.

Can a fuel pump just get weak or something? Any suggestions?

Thanks for looking!

How old is the gas in the tank. Filters and seperators won't always get water and/or dirty gas. The first place I look with those symptoms is the gas itself. If it isn't fresh ie. a fair amount of gas run through the tank It is worth checking. Contaminated gas can clog filters quite quickly.

I did have a coil wire crack that also produced similar symptoms on the same engine you have so after gas look to ignition. Fuel pump wouldn't be my first guess as it seems you are pumping fuel fine up to 3000RPM and should maintain enough fuel pressure in the lines.

I start with the simple fixes and then look elsewhere if the problem isn't found. Hope you find the issue soon enough.
 
QUOTE(Blu @ Aug 15 2009, 09:24 AM) <{POST_SNAPBACK}>Thanks for all the replies! I have already checked the Cap/rotor/ plugs and wires. All looked good. Also, when the tach jumps, it's not a false reading. The engine is bogging down for a sec then ramping back up. Like it's going to stall then comes back to life - repeatedly. It has never backfired either.

I'll start with removing the water seperator and checking it for water. I'll probably add some Sea Foam to the fuel too.

Is it a big job to remove and clean the carb?

Doesn't seem to be heat related. Will happen as soon as I'm coming out of the river from port.

The sea Foam is a great idea and really good stuff. I'd give that a chance to work. I would not rush in to the carb. until you have checked fuel and ignition issues as mentioned above. Given the year and make of the engine it is probably a Quadra Jet carb. They are a good carburetor but can get real finicky when messed with. There are only a few people who are really good rebuilding them and I have seen times where messing with them leads to buying a replacement for big bucks. You are on the right track with the low cost easy fixes. You are not spending a lot of money and everything you are doing is good maintenance for your boat/engine. Check all that stuff out before any removal or disassembly of components. Chances are you will clear it up before getting in too deep. Good luck.
 
Given the symptoms you described and your description of the clogged fuel pick-up screen that you cleaned it is my guess you found the problem. Fingers crossed as well but high probability that was your culprit.

Just a note, it is not uncommon for this type of problem to reoccur until you can run out any contamination in the tank. Not always but it can happen again. Bad thing about boats in this region, they have to sit too long in the winter. They would behave so much better if we ran them all year. At least you will know where to start if it acts up again.

Looking forward to you report.
 
QUOTE(SCMSDON @ Sep 6 2009, 09:56 PM) <{POST_SNAPBACK}>This is not a fuel issue.
What you are discribing makes me think that you are "losing" the hub on the flywheel or the propeller.
Call me @ 586.954.3330 We'll talk about it!
Have a safe and blessed weekend!
DON
Good news. I made it out this evening and she ran like a champ!
Thanks for everyones input.
 
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