Stalls out on idle after 30 to 45 minutes. Mercruiser 4.3 TKS Thunderbolt V Alpha II

dwhildreth

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Oct 14, 2021
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Having a few issues with my Mercruiser 4.3 TKS Thunderbolt V Alpha II (0W671692) that I could use some help with.

The boat runs fine for about 30 to 45 minutes then it stalls out on idle.

Today I noticed the Starboard Exhause Riser was very warm to the touch, almost hot, the Port Side was cool. This doesn't seem right to me.
The Engine temp runs at 160° F

When it started to stall out on idle, I noticed there was a constant and steady, drip, drip, drip, of fuel into each barrel of the carb.

In the recent tune-up and replacement of parts, the two-year-old plugs were dry carbon fouled, each cylinder spark plug was the same fouling.

*It was doing this before the tune-up.

New tune-up and maintenance parts recently replaced all were Mercruiser/QuickSilver:
Plugs (AC MR43LTS)
Plug Wires
Cap
ICM and Rotor
Oil/Fuel Pump Safety Switch
Fuel filter/Separator

Thanks in advance for any help
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
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Welcome aboard

fix your fuel issue - there should be no drip

at idle one exhaust manifold will always be warmer than the other. (hint, its the higher of the two)
 

crazy charlie

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Today I noticed the Starboard Exhause Riser was very warm to the touch, almost hot, the Port Side was cool. This doesn't seem right to me.
You are correct on that. I would pull the very warm riser and check for blockage in the passageways. Also take a look at the manifold passageways as well. Also check the exhaust flapper while the riser is off. Charlie
 

nola mike

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You are correct on that. I would pull the very warm riser and check for blockage in the passageways. Also take a look at the manifold passageways as well. Also check the exhaust flapper while the riser is off. Charlie
No, as Scott said, he's flooding at idle. There shouldn't be a drip. Problem is in the carb.
 

crazy charlie

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No, as Scott said, he's flooding at idle. There shouldn't be a drip. Problem is in the carb.
So your advice to him is to pay no attention to one hot riser and one cold riser after 45 minutes of engine running??? I cant agree with that thought process.

dwhildreth,Your risers are good at slightly different Temps as Scott mentioned..What you are describing is not a slight difference so I would be concerned.It could be a clogged riser or 2 different gaskets/restricter plates on the risers.Thats just a couple of easy to check things that come to mind.Charlie​

 

alldodge

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At idle one riser will always be hotter then the other, and more so on a hose. Depends on the person but about 120* is pretty warm, 130* starts to burn
 

dwhildreth

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Oct 14, 2021
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Thank you everyone for your replies. I was away for a bit out of town.

Yes, I have drips from the jets dropping onto the butterflies, which I'm not exactly sure how to fix.

I know it is a fuel delivery problem, and mostly why it stumbles if I jam on the throttle quickly, slowly it comes right up unless it dies from flooding first.

The float setting in the carb is correct. It's a TKS, and the solenoid does work and pulls off correctly.

The drips seem to occur after the engine warms up and the Starboard Riser gets warm. Not to the hot to touch, but definitely very warm.

I was wondering about the Exhaust flappers but didn't want to tear into them unless I had to and have exhausted (pun intended) all other avenues of possible problems first.

I was talking to a shop owner and he mentioned a failing water pump, which vapor locks the carb. He said you will know this which most miss as the time goes by, the temp will go from one season at 160°, then the next rising to 165°, then the next season 170°......when the air and water temps are high in the summer. When this happens it's your water pump.

Three years ago when we bought the boat, it didn't have a T-Stat in the block and was running cold around 150°.

I corrected this by installing the proper OEM T-Stat and remembering that in the hottest time last year it approached 165°, but no problems, this year it approached 170° when the outside air temp was around 105°, and this year we started having problems.


I'm not sure but after processing this info out, it could make sense and follow the progression of events.

Thanks in advance, and this might be out last week before having to put the boat up for winter.

Was hoping to fix this problem before next season, as we are going to sell for a possible bigger boat, just don't want to sell something to someone that can't enjoy right from the start.
 

alldodge

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Vapor lock doesn't happen with the carb, would need to be EFI or MPI

The problem is the carb needs rebuilt again or adjusted
The float can be adjusted correctly but the needle seat could be leaking. The carb has to much fuel in the bowl and this is the reason it drips and or floods
 

Lou C

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Nov 10, 2002
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If you're getting dripping from the discharge tubes, with the engine off, that means that your needle valves may not be holding and have to be replaced. This can happen even if the float height is correct. Now if its dripping when the engine is running but not when its off, it can be dirty or clogged idle air or emulsion tubes, I had this on my Quadrajet and cleaned it really well and that took care of it. In the carb world they refer to this as nozzle drip.
 

Scott06

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In addition to other carb related problems check you fuel pressure no more than 5-6 psi will overcome the needle and seat
 
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