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comptiger5000
RO# 30050
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 Posted - Jun 19 2010 : 20:39:22
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Recently, my starboard engine has had an intermittent stalling problem at idle. It's a 1986 Mercruiser MIE 340 (454) with a 4bbl Quadrajet. Engine has 1300 hours, carb has never been rebuilt.
It starts fine, runs fine, power is normal, and generally shows no problems. However, last weekend, I was preparing to drop an anchor, throttled it back from about 1000 rpm to idle in forward gear, and it just died as soon as I hit the throttle stop. After a few seconds of cranking, and a strong gassy smell out the exhaust, it re-started.
Today, I was getting ready to leave the dock, let the engines warm up for a few minutes at about 1200 rpm, then throttled them back to idle to prepare to leave. About 20 seconds later, I hear one of my engine alarms squealing. I look over, and see 0 oil pressure on the STBD engine, so I flipped it off. Of course, I didn't look at the tach. I think it had simply stalled, although I didn't hear it die. When I went down into the bilge to look around, I could smell a bit of gas around the carb. I haven't restarted it since then, as I didn't know for sure if it had stalled or lost OP, so I wanted someone else with mechanical knowledge in the bilge when I restarted it, and my father wasn't around.
Any ideas as to what might be causing this?
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1986 Chris Craft Catalina 381 "Hour Glass"
Twin 454 FWC Mercs, Onan MCCK 6.5kw FWC |
Homeport: Stamford, CT
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jtybt15
RO# 3300
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Posted - Jun 19 2010 : 22:15:47
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Sounds like float is stuck open. Smack the fuel inlet connector to try and jar the float and/or needle valve loose.
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Charlie
There is much to be said, in a world like ours, for taking the world as you find it and fishing with a worm.-Bliss Perry, 1904
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Homeport: Ca
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comptiger5000
RO# 30050
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Posted - Jun 20 2010 : 09:05:01
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Alright. I'll be heading down there in an hour or so, I'll give it a shot and let you guys know what happens.
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1986 Chris Craft Catalina 381 "Hour Glass"
Twin 454 FWC Mercs, Onan MCCK 6.5kw FWC |
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Homeport: Stamford, CT
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Brian
RO# 64
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Posted - Jun 20 2010 : 16:48:18
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I had somewhat the same thing happen. We have the same engine. My is an 85 on a chris commander. My problem though I was on the lake and the port engine cut out. I was able to restart it but when power was applied it died in a few seconds. Bottom line I went back on one engine. When I got near my dock I tried to restart engine and it fired up. As i was docking I needed to throttle up to turn and the engine cut out. I am thinking something as simple as the fuel filter but any other advice would be appreciated.
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Homeport: Cedar Point ,Ohio
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Sandy
RO# 1159
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Posted - Jun 20 2010 : 20:44:45
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A basic 1st question for both is when was last full tune-up? All filters, oil, dist cap, rotor, plugs and base-timing?
As Charlie suggests since you mention odor at the carb, stuck float could cause idle cutout & gas odor, or just 1 cylinder not firing at idle speed could also put a little gas in the exhaust and stall. If idle was adjusted lower than recommended (750 RPM in N?) it might not take take much to stall.
Just to be safe, it can't hurt to check the fuel pump sight tube to the carb in case the pump's outer diaphragm is just begiinning to leak.
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| Sandy |
Edited by - Sandy on Jun 20 2010 20:48:58 |
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Homeport: The Vineyard
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comptiger5000
RO# 30050
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Posted - Jun 20 2010 : 22:13:57
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Oil and filter are new at end of last season, have about 10 - 15 hours on them. Fuel filter is a year old (normally replaced every 2-3 years, never had one clog), and probably fine, as it runs fine at 3200. Dist cap/rotor, timing and coil are a few years old (4 or 5), with about 150 - 200 or so engine hours since. Spark plugs were replaced during spring commissioning.
Before I fired it up today, I gave it a good few taps around the float bowl, and then held the choke open and shot some carb cleaner through the primary side of the carb (both with throttles closed and open), and a little into the secondaries. After a good bit of cranking to clear the excess carb cleaner out, and a little stumbling at first, she smoothed out and ran well.
It spat a bunch of oily gunk out the exhaust, with some soft carbon looking crap mixed in. It continued to do this through the warmup period and until I left the dock. I tried idling it back before I left, and it settled down to about 450, and slowly dropping. Once it got to 400, I throttled it up a bit, as it would have stalled if it got much lower.
I ran at about 3100 rpm for 20 mins or so, and by the time I got to my destination, the exhaust gunk had cleared. I kept it a bit off idle just to be safe, so I don't know if it would have idled ok. Coming back in, it idled fine without stalling both when I first left and when I got to the dock, although the idle was a bit low, so I'll have to check it and see what it does next time.
I had bumped the idle up a few weeks ago, as both engines were idling a bit low (manual spec is 650 - 700 in FWD gear, I usually shoot for 700 in N, which gives about 600 in gear. More than that gets twitchy in tight spaces). The starboard was idling about 600 in N, 500 in gear today. I know from past experience that they'll idle smoothly at 450 - 500 without stalling, even in gear.
I checked the sight tube, no fuel. The pump is about 7 years old, as it was replaced when the port one died. Engine doesn't sound like it's missing at idle, and exhaust isn't gassy while running, so I don't think that's the issue.
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1986 Chris Craft Catalina 381 "Hour Glass"
Twin 454 FWC Mercs, Onan MCCK 6.5kw FWC |
Edited by - comptiger5000 on Jun 20 2010 22:14:46 |
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Homeport: Stamford, CT
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talexander38
RO# 31109
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Posted - Jun 20 2010 : 22:55:43
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just might be time to replace the old Q-carbs with 1300 hrs they owe you nothing, you might pore a little sea-foam in to the float tubes it'll clean them out.
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HTC(SW) U.S.N. Retired
You'll Know I'm pissed when you hear the breech lock. |
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Homeport: Hayes Va.
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jtybt15
RO# 3300
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Posted - Jun 20 2010 : 23:54:58
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You have to adjust the low speed air screws and increase idle some at first. They are the two screws on the front of the base plate of the carb. Best way is with a vacuum gauge connected to the pipe plug on the intake manifold between the carb and dist.
The idea is to get the highest vacuum reading at the recommended idle RPM...which has to be readjusted as you turn the air screws. You can do it by ear, too. Just turn 1/16-1/8 of a turn at a time and wait at least 5 seconds for the adjustment to show. Turn in and out to get the smoothest idle. You may have to lower idle if it get's too high.
Could be the carb(s) need cleaning, too. It's not very hard unless you've never done it before.
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Charlie
There is much to be said, in a world like ours, for taking the world as you find it and fishing with a worm.-Bliss Perry, 1904
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Homeport: Ca
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comptiger5000
RO# 30050
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Posted - Jun 21 2010 : 05:27:28
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Alright. I'll try the idle mix adjustment and see what happens. If I can't get it to idle right, then it's time to have this carb rebuilt, being that taxleander is right, it owes me nothing after 24 years and 1300 hours.
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1986 Chris Craft Catalina 381 "Hour Glass"
Twin 454 FWC Mercs, Onan MCCK 6.5kw FWC |
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Homeport: Stamford, CT
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Mercruiser 454 Stalling
