Boat struggles when Warm

Joined
Jul 12, 2019
Messages
13
I have a 2007 Tahoe Q4 with a Mercruiser 4.3 with TKS. The boat has always been very reliable and I have maintained it for the five years I've owned it.

Out of winterization, the boat cranked up and ran fine this year on muffs. I'd taken it out a couple of times with no problems at all.

Last week I went out by myself. Boat cranked up normally, it ran fine. I got it up to about 45 or so, then cruised around 25mph to a cove a few miles away. The boat would have been fully warmed up by the time I got to the cove. I drifted for an hour and a half or so with the motor off. When I went to crank it back up, it did crank, but it was very stumbly. It was running rough. In gear, it died out. I repeated this process a few times, but nothing got better. I eventually was towed back.

I went down to the dock on Monday, and it cranked up normally and ran fine. I ran carb cleaner through it and it was still running fine. After a while though, I guess around the time it was fully warmed up, it began exhibiting the same symptoms. The rough idle, stumbling.

Wondering if it was a fuel problem, I had brought starting fluid. Spraying starting fluid directly into the carb did not help the rough idle, in fact it made it worse, which makes me think there isn't sufficient spark or the fuel is too rich. The spark thing is confusing though, because it ran fine from a cold startup.

I'm now thinking this possibly has something to do with the TKS system? Any other suggestions? I'm going to change the fuel-water separator next, but I'm a bit at a loss. Any suggestions are appreciated.
 

Dillusion808

Seaman
Joined
Nov 20, 2023
Messages
64
Check oil.
When my manifold started leaking it ran fine all day trolling. When we came to back to the dock and brought it back down to idle for the first time all day it died.

Got it to start back up at the wash down but it was rough.
 

Bondo

Moderator
Staff member
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Apr 17, 2002
Messages
70,953
Any other suggestions? I'm going to change the fuel-water separator next, but I'm a bit at a loss. Any suggestions are appreciated.
Ayuh,..... Welcome Aboard,..... When you pull the filter off, dump it in a clear container, to look for Anything but clean fresh gasoline,.....
There's a very good chance, that'll fix it,....
If not, you'll have a very good clue as to what's going on,....
 
Joined
Jul 12, 2019
Messages
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Ayuh,..... Welcome Aboard,..... When you pull the filter off, dump it in a clear container, to look for Anything but clean fresh gasoline,.....
There's a very good chance, that'll fix it,....
If not, you'll have a very good clue as to what's going on,....
So it was clear. The gas was a bit more yellow than I'd expect but it smelled fine. Changed the filter anyway. Added stabil marine treatment and also ran quicksilver Power tune. The boat did want to hesitate a bit after all that was through and it was at operating temp but it seemed improved. Did not stall out and while It stumbled a touch when I increased revs it quickly recovered and revved smoothly.

I didn't take it from the dock because it was getting late. I'm going to add fresh fuel and maybe more stabil treatment and see what happens.
 

dingbat

Supreme Mariner
Joined
Nov 20, 2001
Messages
16,072
I didn't take it from the dock because it was getting late. I'm going to add fresh fuel and maybe more stabil treatment and see what happens.
Save your Stabil treatment until winterizing.
Stabil is a fuel stabilizer. Can't fix something that is already broken.
 

Bondo

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Staff member
Joined
Apr 17, 2002
Messages
70,953
So it was clear. The gas was a bit more yellow than I'd expect but it smelled fine. Changed the filter anyway. Added stabil marine treatment and also ran quicksilver Power tune. The boat did want to hesitate a bit after all that was through and it was at operating temp but it seemed improved. Did not stall out and while It stumbled a touch when I increased revs it quickly recovered and revved smoothly.

I didn't take it from the dock because it was getting late. I'm going to add fresh fuel and maybe more stabil treatment and see what happens.
Ayuh,...... I'm guessing that enough crap might have passed the filter, 'n a carb rebuild is in yer future,....
 
Joined
Jul 12, 2019
Messages
13
Save your Stabil treatment until winterizing.
Stabil is a fuel stabilizer. Can't fix something that is already broken.
I used the stabil marine tune up that's supposed to help clean the fuel system. Fuel was stabilized at winterization.
 

nola mike

Vice Admiral
Joined
Apr 22, 2009
Messages
5,362
I'm now thinking this possibly has something to do with the TKS system?
Probably not if it wouldn't start both after cooling for 1.5 hours (assuming ignition off ) and it started running rough while underway on a separate occasion. If the plunger was stuck open or closed you'd have problems only in one of those instances. Have you checked them tank vent yet? Still sounds fuel related but easy enough to test.
 
Joined
Jul 12, 2019
Messages
13
Well after all the fuel treatments, cleaning the carb and topping off with fresh fuel and a can of seafoam plus star tron for good measure, shes back up and running again. Went 6 or 7 miles with four adults and a full cooler and she did fine. Cranked right up to come back home. I guess she's fixed! Thanks for the replies.
 
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