Mercruiser 4.3 TKS won't idle

tilzinger

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I've been scouring the webs and have run across multiple similar posts to what I'm about to describe, but mine is a little unique.

We have a 2011 Larsen with a 4.3 TKS. This summer the first day out on the lake the motor didn't want to idle. Basically in neutral or when going slow through a channel it would die, and when it doesn't die it feels rough. Giving it throttle kept it going, so at cruising speed it runs fine. The day started fine, then it wasn't until we anchored for a bit, then started it again did we have trouble. On the way back to the ramp we heard a very audible single click noise from the engine (my wife and I both looked at each other at the same time when it happened) and it magically fixed itself. The motor instantly started running smoother at idle speed and did not die. The next weekend we went out it was fine the entire day, no issues at all. Fast forward another 3 weeks and we go out again and the same thing is happening. It dies at idle speed. Unfortunately it did not magically fix itself this time.

I have looked at the carb and every bolt, screw, throttle cable, attachment etc and nothing seems obviously loose or broken. I'm not a mechanic, so my skills are very limited when it comes to this thing. The most I've done with motors is change various filters and spark plugs and know when a starter is broken. I took the filter thing off the top of the carburetor and it looks really clean on the inside (from what I can tell without taking the thing apart). I've read similar stories about water in the gas, dirty carb, etc etc, but given that we heard a mechanical click sound that fixed the issue, its obviously something else, but I can't tell what it is. I'm feeling like something is getting stuck in a position its not supposed to be in, and then somehow it released itself when we heard the click. Does this sound familiar to anyone?

Thanks for any help provided.
 
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alldodge

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Howdy

Your pic link doesn't work, but that's might be OK for now. The TKS carb has a module mounted to it that has a plunger at the end. Its not very big, but what it does is supply more fuel when the motor is cold. Once the motor warms up it should close off and the motor gets a little less gas. If it doesn't close off then the idle is rough. While you might have another issue this one is probably the big one currently.

The click you heard may have been the module (kind of like a solenoid) quickly moving the plunger into close position. In the link below item 1 is the module.

http://www.mercruiserparts.com/bam/subassembly/31493/12833/80
 

tilzinger

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Yep, it starts like it always has. The last time we were out it ran for 10-15 minutes then started acting up. My wife was on the lake while it idled waiting for me to park the trailer and she said it ran fine, then after I got on the boat and we headed out it started acting up. Maybe the boat doesn't like me personally :D
 

alldodge

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When was the last time the fuel filter was changed?
Take the fuel filter off and have a baggie. Pour the contents into the baggie and see if there is anything in there except clean gas.

If filter has not been changed, refill with clean gas and put a thin coat of motor oil on the gasket and screw into place.

If there is any water it will separate (oil and water). If there is crud found we might need to thing about something else.

Next time motor is started listen to it and there should be a hiss going on, and this hiss will change as it warms up. If it does this is good, if it doesn't then there may be a TKS module issue
 

tilzinger

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Thanks for the info, I'll try to take a look at the filter today or tomorrow. TBH not sure about the fuel filter. I know the oil is changed along with the filter every fall before winterization.

Speaking of running the motor, is this all I need for my model to run it on land? E.g. I don't have to run water to the motor with a 2nd hose or anything? Just slap one of these on the lower casing over the holes?

https://www.walmart.com/ip/Attwood-U...&wl13=&veh=sem
 

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alldodge

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Yes attach the hose to the ear muffs
ears.jpg

and cover all the holes on each side of the lower section of the drive. Turn water on full, and don't rev the motor over 1500 rpms. Just let it idle will be more then enough
 

tilzinger

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So if it is an issue with this module thing, is there a way to force it to the closed position until I get it to a shop for repair?
 

alldodge

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So if it is an issue with this module thing, is there a way to force it to the closed position until I get it to a shop for repair?

There might be but have not heard of anyone doing it, and if so don't see it being done without disassembly and a modification. Its easy enough to replace, just a couple screws and an O ring. Not saying to go get one, because we need to test to find out if that is the issue. Do you hear a hissing that does stop?
 

tilzinger

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Heading to the lake today and haven't had time to get muffs, so I'll know later this evening.

I did see the 2 screws so it does look like an easy thing to replace if I need to do so.
 
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