I've got a Mercruiser 4.3 TKS with the alpha drive. It idles, revs fine in neutral. When I put it in gear, I'm good at idle speed, but when I try to plane out, it stalls. If I push the throttle forward in neutral it revs right up. I was thinking clogged fuel filter, but that should stall it out in neutral or gear engaged.

Sounds like you need the carbertor rebuilt to me .

Sounds like your on the right track. It will rev in neutral because its not under a load. First time in the water this year?

Run you some sea foam through it before you take the carb off. Couldnt hurt to see if it will clear it up.

The two previous posts sound like the are from more mechanically skilled users than me, so take this for what it is worth.
Water in my gas(90 HP outboard) caused same issues last year. Had to get some gas out, place in a coffee cup for several hours. Water will settle on bottom. Had to then check filter and clean carbs and then replace gas.

Happened again a month later. Found main fuel line hose from side of console to top of the tank had dry rotted and was allowing condensation to get in.

It can do that if its sucking air too. All my problems are with outboards and disels now days though.

Changed the fuel separator an no luck. I tore the carb down and it was all gunned up. I cleaned it and good to go. Running seafoam through the next few tanks.

The weird thing is a supposedly have always used ethanol free gas, run startron in every tank. When I winterized it last year, I dronwed it out with seafoam. This is the 5th carb I have replaced or rebuilt this year (boat, pressure washer, mower, etc.). This has needn't the worst year ever for carbs.

Doc, glad you got yours fixed. Since you have I would like to throw my issue out there I'm having with almost the same motor.

I recently purchased a pontoon with the 4.3 mercury v6 mercruiser I/O with the alpha one outdrive. Put it in the water this weekend with a new battery (old one we had to jump off the day before and 6 years old so I replaced it that day) and rode around strong for 45 minutes no problems and no stops. When I went to pull back in the slough and put it in idle it cut off. Everything was dead as a door nail, no radio, no horn, no power period. Was worried it was the alternator, but when I went to charge it I hit battery test and we were already at (13 in the good range). I know the previous owner had problems with the bilge not cutting off, horn not working, and radio issues, but had them fixed them prior to the sale. I charged the battery some anyway and the next morning cranked right up and ran like a top. It was holding a charge on the gauges. Does this sound more electrical or not necessarily?
Thanks

Sounds like you have a short, poor connection, or partly broken wire now. Good luck chasing it down. Those gremlins can be hard to find.

Or a circuit breaker tripping, as a result of one of the above.

Sounds like a wire grounding out somewhere.

Could be as easy as a loose battery cable. They will drive you crazy on a boat.

I'm beginning to think the seafoam left in the tank is the culprit. I've have several carbs mess up and we use ethanol free gas as well in all our saws, power equipment, 4 wheelers, etc. Only thing I run at times is the seafoam.

God Bless,
David B.

seafoam ain't worth a flip, most folks in the marine industry do not use it, they may sell it to make a buck, but they won't use it. I use marine stabil and yamaha ring-free in everything I own and have never once had to pull off a carb. When I went to school at yamaha years ago, they had two identical motors sitting on a table that were cut in half so that you could view the short block as it was put together. One motor never had anything ran through it, the other had yamalube ring free ran though it for its entire life. Both motors had 20,000 hours on them. The ring free motor looked brand spanking new, even the exhaust valves. The other motor was carboned up bad. That told me what I needed to know.

Thanks for the replies. Hope to find it soon