4.3 Mercruiser TKS all of a sudden stopped planing and maxes out at 2500 RPMs in gear

[Steamin Seaman]

I hope to provide all the information needed for you pro's out there. So i replaced a coil, cap and rotor and an ignition module, because i wasnt getting fire. I made very sure to replace the plug wires in the EXACT same format. i took it out and she ran like a new kitty cat. i took it out of the water, went to a party, came back with family and friends, and she ran great as we proceeded to the party cove. after a while, we decided to cruise the river, thats when it happened. we were cruising about 4k RPM at somewhere between 35-40 MPH. i backed off as i saw some logs and then when i went to throttle again, it only sputtered at 3k and maintained idle speed. i have noticed the therm never read above 140, so i figured it wasnt opening and replaced with a 160 degree thermostat. she ran above the 140 and i thought problem solved. i took it out on the water, same same. idle all day just fine, rev up in neutral just fine, idle speed around the bay all day just fine, but bogs when throttled and stalls around 3k RPM. checked my fuel/water seperator and seems ok. thoughts???? thanks guys.

oh yeah, its an 08' Tahoe Q7i with a 4.3 TKS, carb. no motor serial number, sorry.

 

[alldodge]

There is a screen filter behind the fuel line (item 29) which needs to be checked
http://www.mercruiserparts.com/bam/s...31492/11812/80

Check fuel pressure at the carb, it should be 4-7 psi from idle to WOT.

Look above the starter for a plate which should have the serial number on it

 

[Steamin Seaman]

I will check that tonight. How do i check the psi?

 

[alldodge]

I will check that tonight. How do i check the psi?

Will need a vacuum fuel pump gauge. Can be found at most any auto parts store
https://www.amazon.com/Actron-CP7803-Vacuum-Pressure-Tester/dp/B0006V2BS2

Then you need to get it connected between the fuel pump and the carb. This requires a fitting to be placed in line so the carb can be connected back up, like this which is a Merc part 91-18078



Or you can do it by using rubber fuel line and making a Tee to connect. For a quick check without a Tee, just connect the fuel line direct to the gauge with fuel line to see how the pump is working without the motor running (would need to hot wire the pump (or bypass the oil pressure switch)

 

[Bondo]

checked my fuel/water seperator and seems ok.

Ayuh,..... Welcome Aboard,.... How'd ya Check it,..??

Unscrew it, dump into a clear container, throw it away, 'n install a new one,..??

 

[Steamin Seaman]

I plan on installing a new one. I poured the contents into a clear glass jar. I also left it off for 24 hours. When I went back to it, the metal had corrosion, gasoline doesn't corrode like water, so I'm getting a new one.

 

[Steamin Seaman]

Replaced strainer (#29) and fuel/water separator. Still bogs down. Getting voltage to pump will measure the psi when my friend returns from his vacation. Still can't find a motor serial number.

 

[alldodge]

Replaced strainer (#29) and fuel/water separator. Still bogs down. Getting voltage to pump will measure the psi when my friend returns from his vacation. Still can't find a motor serial number.

If your pressure turns out to be OK then need to clean/overhaul the carb.

 

[Steamin Seaman]

Replaced all the spark plugs and the fuel pump. Still does the same thing. Revs 100% in neutral, can't get above 2600 rpm in WOT. I am sick of shelling out money for parts that don't fix the problem. What else could it be???

 

[alldodge]

All motors need the same things to create power. Air, fuel, spark and timing. If the motor has good compression then there should be power. Yours does not have the power it should so I would start with the basics, something is missing.

Check compression

 

[Rick Stephens]

Carburator rebuild, as AD stated in #8.

 

[Steamin Seaman]

@AllDodge: took apart the carb and soaked it for a while in parts wash. Took the lower side to the marine shop to verify the gaskets fit. Shop mechanic suggested taking off the Venturi and removing the screw in the bottom of the bowl. When I removed the screw, there were two holes that were channels through the carb. I sprayed the right one with carb cleaner and it went right through the channel. When I sprayed the left, nothing happened. So I sprayed the other end of the channel and worked back and forth on that channel for a few sprays. I didn't see anything specific come out, but I soon had a stream of carb cleaner shooting out the other end. I put it back together and made a few small adjustments to the screw and BAM, we were running like a top again. Put her on the water and she planed out like normal. Thanks Alldodge and Rick.

 

[Rick Stephens]

Great.