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4.3l Merc cruiser always seems to choke even when hot and…

4.3l Merc cruiser always...

4.3l Merc cruiser always seems to choke even when hot and runs rich.

Mechanic's Assistant: Sometimes things that you think will be really complicated end up being easy to fix. The Marine Mechanic I'm going to connect you with knows all the tricks and shortcuts. Tell me a bit more about what's going on so the Marine Mechanic can help you best.

Having issues with boat always seems to revert to cold start and chugs for a short peroid

Mechanic's Assistant: Sometimes boat issues seem like they'll be really complicated, but end up being easy to fix. The Marine Mechanic I'm going to connect you with knows all the tricks and shortcuts. Is there anything else the Marine Mechanic should be aware of?

Also had issues with temp gauge wasn't working so we ran a new earth to block as new sender and gauge didn't change anything, was thinking it could be related

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Answered in 6 hours by:
1/20/2018
Jason
Jason, Marine Mechanic
Category: Boat
Satisfied Customers: 18,228
Experience: Degree in Marine Technology. Gas and diesel marine mechanic.
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G​ood morning, my anme is Jason, whom am I speaking with? I read what you wrote. Mercruiser engines are cataloged by serial number. Can I get that number so I can look up and see exactly which version of the 4.3 you have.

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Customer reply replied 7 months ago
My names Michael, the serial is 0W347261 it's a tks Carby. So issues being having incorrect temp readings >50 the gauge works and gets a signal from sender but clearly not correct. We have tried new sender and gauge. The other issue being runs very rich in start and until warmed up and then runs great, if you turn off and on within a few mins it does a cold start and runs rich again for a short time. Iv thought it could be the mixture screw\s but can't find where they are, or are they accessible at all? see picture attached.We have check forward idle is good.
Customer reply replied 7 months ago
50 deg celcuis btw
Customer reply replied 7 months ago
We can take sender out, earth it and put in cup of hot water and it works well. So we figure earth issue and ran a temp new earth to battery and block and block to sender
Customer reply replied 7 months ago
Still doesn't work tho. Sender is wet in removal so it's not being blocked from hot water.

Good morning and sorry for the delay. When you replied back last night I had already logged off for the evening. My system also says that you are in the AU. I am in the US so there is going to be a large time difference between us. Can you be more specific by what you mean by running rich? Is there a strong odor of burned or unburned fuel from the exhaust? Is there black smoke from the exhaust? What exactly is it doing or not doing?

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Customer reply replied 7 months ago
Black smoke and even can see some small amounts of fuel floating on water when sitting still.

Got it. Black smoke can be caused by a few things, but the primary cause is low engine compression. Have you compression tested the engine yet? If yes, what are the numbers? If no, are you able to perform a compression test on the engine?

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Customer reply replied 7 months ago
I can't do that myself no, would it not always so this tho? It only does it when cold start or on restarting for short periods as if it's over choking when cold and unneededly choking when warm start?
Customer reply replied 7 months ago
I was thinking it might be an issue with turn key start because of this.... We have poor temp readings and turnkey has its own temp sensor too which if is also getting poor temp reading may think it's always cold starting?

100 PSI is the cutoff point for compression. 100 PSI on up is a pass, 99 PSI on down is a fail. Your engine could be teetering right on edge. On the turn key start, are you near the engine now to run it for a quick test?

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Customer reply replied 7 months ago
Sorry no it's packed away away from my location.

When can you get out to it?

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Customer reply replied 7 months ago
Could see about it tomorrow but time difference will be issue, if you could give me a kinda to do list we can give you our results

I​f you want to see if the TKS is working correctly all you need to do is listen for the whistle. What you want to do is pull the air filter off the engine. Start it up, and listen. If the TKS is working correctly what you should hear, is you should hear a whistling sound coming from the carb. This whistling should continue anywhere from 3 to 10 minutes depending on how cold it is out side. As the engine warms up, the TKS module will close, and the whistling noise will stop. So what you want to do is 1, make sure you can actually hear a whistling noise from the carb and 2, make sure that noise stops after 3 to 10 minutes. Does that make sense.

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Customer reply replied 7 months ago
as I know there are 2 temp probes 1 for tks 1 for boats temp gauge, the boats gauge reads just under 120 when warm which can't be right. Sender and gauge works good when sender is connected to boats electrics (using a temp Earth wire) but NOT in the block. Soon as you put it in block it reads low again.

Did you read my last response?

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Customer reply replied 7 months ago
that makes sense to me. We can do that
Customer reply replied 7 months ago
Got it
Customer reply replied 7 months ago
if no whistle need go rebuild Carby? If it does whistle cold AND hot?

I​f the whistle sound isn't doing what it's supposed to do (as I explained above) then we need to dig into the TKS electrical circuit deeper in order to figure out why. If it is doing what it's supposed to do, then it's working as it should, and you really need to have that compression test done next.

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Customer reply replied 7 months ago
Got it, will check this step asap.

When will I hear back from you, tomorrow some time?

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Thank you
Jason

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Customer reply replied 7 months ago
It will likely be more 12 hours from now

12 hours from now will be my bedtime. If you respond back when I am offline I will reply back the next time I am on.

Jason
Jason, Marine Mechanic
Category: Boat
Satisfied Customers: 18,228
Experience: Degree in Marine Technology. Gas and diesel marine mechanic.
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Customer reply replied 7 months ago
That's OK, I will l sort that out.

Sounds good. I will catch you later.

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Customer reply replied 6 months ago
tested tks, whistling starts and goes away after short time and boat runs well. Turn boat off for few mins and back on and it runs poorly (needs manual throttle to idle).Could there be an issue in the thermostat housing getting poor flow to both temp senders as its only thing that makes sense as BOTH tks and gauge senders don't appear to work correctly or are just not getting the water to them to transfer heat well enough. Boat doesn't run hot so thermostat must be OK could a water pump be giving poor flow or something or do you still think it's electrical?We have testes all the wires, we used s temp new signal wire to gauge, no go, earth out the gauge signal jumps to Max temp put back into sender moves up slightly to 120f only. Have tried new sender for gauge tstat too.block is earthed Ok, sender body is earthed Ok when in block. Which makes me think it's an issue in the thermostat housing??

Good morning. When you run the engine are you running it on the garden hose or is the boat in the water? Also, is there any story or history to this, have you ever personally seen this engine run correctly?

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Customer reply replied 6 months ago
it was in water when testing. To my knowledge it 6 months ago or so it had tempretures readings and would run on.

I​f the whistling sound is stopping then the TKS is working as it should. If anything you might have a thermostat that is stuck open, and not allowing the engine to heat up. What we would do I in the shop is use an infra red temperature gun and scan the thermostat housing and see if the readings on the temp gun agree with the readings on the gauge. If both the temp gun and gauge read low, then the thermostat would be stuck open.

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Customer reply replied 6 months ago
to pull the thermostat housing off is there any issues with re sealing or gaskets? Will look at the thermostat and test in hot water too if not too much drama

Y​ou would definitely want to use a new gasket and or oring. Click this link for a picture. Merc used 2 different types of thermostat housings on your engine. The serial number does not tell me which one you have, it only shows both possible options - http://www.mercruiserparts.com/bam/subassembly/31492/11812/170

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