Minor Surging After Carb Rebuild - TKS 4.3 '06

civikminded

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Hello, looking for a few ideas of things to check on my 06 Crownie with a 4.3 TKS Merc Alpha I/O.

Boat was idling like crap, stalling out etc. My trusted mechanic recommended rebuilding carb. Boat now runs like a dream on muffs. Run PRETTY MUCH like a dream on the water, but has picked up some minor surging since the carb rebuild. Between ~1.5k - 3k it has a 200 RPM surge. WOT runs beautifully. Also desiels a little bit after some hard running. Mechanic is in a tough position because the issue only happens when the boat is under actual load.

My next idea was to try to re-do the idle mixture and curb idle settings when the boat is on the water and hot. Does that sound reasonable? Any other thoughts on what I can check? This didn't happen before the rebuild. Also new fuel filter, cleaned up the distrib rotor, clean gas.

Boat is so close to being "perfect" after running like crap for a couple years! Appreciate any pointers!
 

Lou C

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Are you sure there are no vacuum leaks (gasket under the carb, any vacuum lines hooked up to the choke pull off, etc). Carefully make sure the bolts holding down the carb are snug (do NOT over tighten). I had a slight uneven idle condition on my Quadrajet that was solved by replacing the thick base gasket used on these.
 

alldodge

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I'm thinking need to get back into the carb for adjustments

What are the compression numbers?
 

civikminded

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Are you sure there are no vacuum leaks (gasket under the carb, any vacuum lines hooked up to the choke pull off, etc). Carefully make sure the bolts holding down the carb are snug (do NOT over tighten). I had a slight uneven idle condition on my Quadrajet that was solved by replacing the thick base gasket used on these.
Thanks this might be the culprit if he didn’t get the carb on right when he rebuilt. Like I mentioned, it doesn’t happen on muffs so he wouldn’t have caught it. I’ll probably take it back to get checked if some other simple troubleshooting doesn’t work.
 

civikminded

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I'm thinking need to get back into the carb for adjustments

What are the compression numbers?
I might try to find a marina that could adjust it "hot and wet" since the problem doesn't show up on muffs. I might try it myself - I know enough to be dangerous but this TKS carb scares me a little bit. Do you think it could just be an adjustment problem or something you need to tear the carb up again for?

I'm not sure what the compression numbers are at this point.
 

Lou C

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If it does not do it on the muffs but in the water it’s related to the load on the engine.
 

alldodge

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If compression is low, then that would explain why it doesn't do well in the water.
 

Lou C

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The Merc TKS carb, is this just an update of the old Rochester 2bbl? If so nothing to be afraid of.
 

Lou C

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Sounds like the fuel mix in that range is too lean hence the surging
 

civikminded

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Sounds like the fuel mix in that range is too lean hence the surging
OK I think I'll take 'er out and try to adjust the carb hot and wet as a first step. You and my mechanic would get along, he kept telling me "its just an old Rochester 2 barrel" :)
 

Lou C

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Like I had on my ‘72 Chevrolet 5.7
Now the Rochester 4bbl Quadrajet, that’s a complex carb. I’ve had mine apart a few times….
 

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achris

More fish than mountain goat
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Between ~1.5k - 3k it has a 200 RPM surge. WOT runs beautifully.
Not sure if I've posted this or not... Spark plugs...

I've seen this EXACT symptom on many 4.3s, and it's ALWAYS been fixed with a new set of plugs. I think the previously poor carb condition was disguising it. You've replaced the coil and cap, how about you replace the ignition component that gets the really rough end of the pineapple ALL THE TIME, the spark plugs...

Can't hurt, and will probably fix it.

Chris..........
 

civikminded

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Not sure if I've posted this or not... Spark plugs...

I've seen this EXACT symptom on many 4.3s, and it's ALWAYS been fixed with a new set of plugs. I think the previously poor carb condition was disguising it. You've replaced the coil and cap, how about you replace the ignition component that gets the really rough end of the pineapple ALL THE TIME, the spark plugs...

Can't hurt, and will probably fix it.

Chris..........
OK Thanks Chris, If carb tuning doesn't help I'll probably try this. Ive been avoiding doing it because jeez, Crownline are nice boats but they have hellish motor access and the plugs are buried down in there.
 

Lou C

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Does your boat have removable side panels next to the engine? Taking them out makes it an easy job. Sometimes because of the design of the exhaust manifolds you might have to use a thin wall spark plug socket.
 

achris

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OK Thanks Chris, If carb tuning doesn't help I'll probably try this. Ive been avoiding doing it because jeez, Crownline are nice boats but they have hellish motor access and the plugs are buried down in there.
The fact that they're difficult to get at makes me think they may not have been changed in a while. Those engines 'eat' spark plugs. If you're not changing them every 200 hours, you're going to get ignition issues, like surging at mid range...

Chris....
 
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