BGS

Bogs down under load

9 posts in this topic

2002 Chap 186SSI 5.0 Merc with Carb. Always use non ethanol gas.

I had my boat de-winterized, oil, filters and impleller changed last month, took it out twice this year and it ran fine. Then when I went out for the third time it ran fine until I shut it down to float for a while. When I started it to head in to the dock, it bogged down under load. Won't plane out, and wont go over 3,000 rpm. Took it to the shop and they said it runs fine in the shop, checked fuel pressure which was good. I thought maybe it was an over load of Staybil and whatever the shop winterized the gas with so I put in 30 gallons of fresh 87 octane, non-ethanol gas. Back to the lake, bogged down at first then started running good. Figured it was bad gas in the lines. After I shut it down to float it wouldn't run right again for the rest of the day. I'm thinking Carb issue, but am up for any suggestions. Idles fine. Ran great all last year.

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It could be a number of different things, and I am by no means an engine expert.

But, I had the same problem a while back. Right out of the marina it would run great, no problems, but after a while especially if I was cruising at low speed I would lose all of the power when trying to get on to plane. Would not get past 3000 RPM at all. But then, sometimes it would fire right up on to plane and run great. Tried all of the same things you did with regards to gas.

Had it in for service, could not figure it out the first few times and ran fine at the shop. They took it out on the lake and after some time reproduced it. Back to the shop and after going through everything in detail it turned out to be a short in one of the spark plug wires causing it to miss on a cylinder. The wire would only short out when the exhaust manifold got hot enough (the spark plug wire was too close to it) and then it was hit or miss. Sometimes it never happened.

Long story short, replaced the spark plug wire and no problems since. So I guess my point is, check your spark plug wires to makes sure they are all in good shape. In my case, a casual inspection of the wires did not show the problem because it was a hard thing to see. But pulling them off and inspecting them all in detail revealed it.

It certainly sounds like you have an intermittent miss on a cylinder which will cause the exact problem you are experiencing. And it can be hard to notice or tell that it is missing and running rough.

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Check the carb inlet screen. Fuel pressure is checked after the filter/separator and before this little filter. It is located in the fuel bowl housing at the extream end of the fuel line as it enteres the carb. Pretty hard to over Sta-Bil.

W

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Thanks, I will check both and bought some seafoam to run through it. Even though the boat doesnt have many hours, it is 10 years old. Probably time for new plugs and wires anyway.

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Ran 2 cans of Seafoam and two bottles of Heet through it, it bogged down off the trailer and for a few minutes, then started to spin up so I ran laps around the lake for about an hour at WOT and now it seems to run fine. Guess it was either water or gummed up carb. Thanks for the advice. BTW inlet screen was clean, but now I know where to check.

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On the in-line fuel filter on a Quadra-Jet, 2-Jet, or 2 bbl. MerCarb (like yours) one will want to check for fuel leaks at the fuel filter fittings with the engine turned off after the engine has been run for a few minutes.

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When was the last time you had a tune up? Look for corrosion under the distributor cap and on the rotor. Check your plugs & ignition module.

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I have 185 hours on the boat, and I'm sure it has never been tuned up as it had about 60 when I bought it. I think the bogging down problem is fixed but still feel that it lacks power out of the hole. I ordered Cap, Plugs and Wires from Rock Auto to see if that helps the holeshot. If not I may try a 17 pitch prop even though that seems a little extreme for that boat.

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What you describe in your original post is pretty much what my boat did. Then I was idling back into the harbor and it died & wouldn't start. The mechanic came out, and it started (of course). He took the distributor cap off and showed me the corrosion on the contacts & rotor. Then he pulled a plug, and you could see they needed to be replaced. Fixed it all, boat ran fine in the slip. Everyone got in the boat I put it in gear and it died and wouldn't start. Called the mechanic, he came back pulled the ignition module, and now the boat runs great. If after you change cap, plugs, wires and it still runs bad, check the module. It is located under the distributor. Good Luck!

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