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Weak Idle, Stalling Out


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So I tried to search this issue and there were quite a few explanations but they are going right over my head :). Definitely a novice mechanic. I just got my 1995 Malibu Sunsetter on the water for the first time after winter storage in the mines. I stored it with 2/3 tank of gas and topped it off before putting it on the water. On the ramp it started great and would idle and run at low RMPS without issue. After only 10 minutes it began to have a weak Idle and would at times stall out. Anytime I'm at the higher RPMs it seems to be running strong. When I come down to low RPMs in gear or come out of gear it goes right back to the weak Idle or stalls out. When I lifted the cover I noticed a very very small amount of smoke or steam from either side of the flame arrestor. Any advice? Should I consider a fuel additive? Running a MerCruiser 350 Mag.

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How's the engine temp? If that's high you need to check out your raw water impeller. 

If temp is okay I would change fuel filters.

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Engine temp is normal and the impeller and housing were just changed last July. Where is the best place to get a fuel filter for a MC 350m?

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I don't see myself blowing up the boat changing a filter so I'm going to give that a try! Is there a Fram or Napa equivalent that I could pickup today?

 

Thanks!

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2 minutes ago, thomasjg23 said:

I don't see myself blowing up the boat changing a filter so I'm going to give that a try! Is there a Fram or Napa equivalent that I could pickup today?

 

Thanks!

Not a good way to answer that, you need to see what you have.  Mercury motor could have just an inline filter or also a water separating filter.  If you have a water separating filter then when was the last time you changed it?

 

Inline filter is on the left side of the engine down low on my inlaws Merc powered 04 LXI and the oil filter looking water separating filter is on the right side if I recall correctly.

Edited by oldjeep
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I have a question. If your getting steam outside of the flame arrestor how is that a fuel delivery problem. I do agree that you should always have clean filters but a clean filter has nothing to do with steam coming out your flame arrestor. 

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3 hours ago, thomasjg23 said:

I don't see myself blowing up the boat changing a filter so I'm going to give that a try! Is there a Fram or Napa equivalent that I could pickup today?

 

water/fuel seperator: 3225 gold series Napa

The mercury filter probably can be had at a wal-mart too.

 

Napa should be able to cross check with the Merc Number:  35-802893Q

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When was the last time you had the carb rebuilt? My guess is either a stuck float or needle. The smoke you see is from the carb leaking into the hot motor and steaming off per say. Usually but not always a clogged filter will cause the boat to stall at high speed because it can't get enough fuel and starves itself. Low speed or idle is fine because it can get the required fuel.  

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Here's a test: have the boat in the water, start the engine and make sure it's idling smooth, then rock the boat side-to-side (gently) getting about 6-10" of height variation on the gunnels; If the engine dies you need to investigate the distributor shaft bushing. In my '93 the distributor shaft bushings has worn out at ~900 hours and it really seemed like a carb problem with floats, fuel leakage, and the like. I had the carb rebuilt and the problem persisted, then when troubleshooting I had to hop across the boat when the engine was running, as the boat rocked the engine died. It would fire right back up without a problem, but rocking the boat at idle would cause it to die. I tried the same thing with the engine revved up to ~1500 RPM and it wouldn't die (centrifugal force of the distributor shaft held it in place). I pulled the cap and when I was pulling the rotor discovered that there was waaay too much movement in the shaft, so I pulled it and went to a local auto parts store (Napa/Stewart Industrial Supply). The parts guy at the counter looked at it and gave me an ol' timer speech "I can get you a new one in about 3 days, or I can press a new bushing on there in 20 minutes for $5." 

He pressed the bushing on to the shaft and I had the boat back up and running that afternoon, I didn't have any more ignition problems as long as I owned that boat. (sold it with ~1600 hrs)

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As an update, I added stabilizer and there wasn't much improvement, I changed the fuel filter and it started running much better but still struggled with the stop, go, and low RPMs of wakeboarding (I ripped some arms out). The biggest improvement came from two dang zip ties that I just added today. I pulled the fuel line away from the motor and it really helped. I haven't gone back out to ski to test that it truly is fixed but I'm crossing my fingers. Updates to come.

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On 6/14/2016 at 7:19 AM, thomasjg23 said:

So I tried to search this issue and there were quite a few explanations but they are going right over my head :). Definitely a novice mechanic. I just got my 1995 Malibu Sunsetter on the water for the first time after winter storage in the mines. I stored it with 2/3 tank of gas and topped it off before putting it on the water. On the ramp it started great and would idle and run at low RMPS without issue. After only 10 minutes it began to have a weak Idle and would at times stall out. Anytime I'm at the higher RPMs it seems to be running strong. When I come down to low RPMs in gear or come out of gear it goes right back to the weak Idle or stalls out. When I lifted the cover I noticed a very very small amount of smoke or steam from either side of the flame arrestor. Any advice? Should I consider a fuel additive? Running a MerCruiser 350 Mag.

Probably nothing, but could you please elaborate on this?  Were you running at the boat ramp, or on it (and out of the water)?  Between that comment and the steam I can't help but wonder if somehow the impeller is toast and overheated the engine...

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