2009 4.3L Mercruiser TKS stalling out

[Cecil Diesel]

I just bought this boat the other day. It ran great on the muffs. The boat originally had 3/4 tank of fuel in it and the owner said he only ran it twice last year. I put sta-bil in it and topped the tank off with new fuel before I went to the lake. The boat struggled a little bit to start and then it was running lower rpms at idle then it should. So I got it off the trailer and put it in gear and it would stall out. Finally got it going good enough to run but would only come up to 2100 rpms while in gear. If I took the throttle linkage off and controlled the throttle by hand it would get to max rpm. If in gear under load it would stall around 2100 rpm.

My first thought was bad gas. So I ran it that night and some the next morning until I was at 1/4 of a tank. I also put carburetor cleaner injected into the bowl of the carburetor and put a can of sea foam in the fuel. Then I pulled the boat out and put 87 octane fuel in it. Put it back in the water and immediately I noticed higher rpms at idle. I took off and the boat ran great. It ran great all day while stopping several times to swim.

Then the next day went out to run it again and the boat stalled out again for several hours before I finally just pulled it out of the water. My mechanic by talking to him on the phone seems to think its a carburetor issue.

I would like to get some other opinions. Could it be the old gas still causing issues? Why did it run great one day and bad the next?

 

[alldodge]

Agree sounds like carb issue
Had 2 year old gas which was breaking down. Put in fresh gass which also helped break things loose and now the carb is clogged up, needs rebuilt

Remove the gas filter and dump the contents into a clear container to see if there is anything there but clean gas. Do not reuse the old filter

Since its a new to you boat, also need to do some maintenance
Pull drive and check alignment
Change drive lube
Check gimbal bearing
Check and or replace bellows
Change motor oil and filter

 

[Rick Stephens]

AD is spot on. Do all the regular maintenance, must assume the previous owner didn't do it. Get the regular Mercruiser manual and go through it. You can find the manuals at www.boatinfo.no for online access, you can buy them, sometimes you can find a PDF version from someone. The maintenance is essential. Even though I built my power system from the ground up and know everything is good, I still pull the drive, check alignment, change oil in drive and motor, grease u-joints, inspect bellows and gimbal bearing, and coat everything that can get corroded with 2-10C grease and reassemble every year.

Pouring chemicals in the tank only adds more factors into a fuel problem. It doesn't actually fix anything. Pull the carb apart and kit it. Make sure every passageway is clean and open by running fishing line or wire through them. Check the inlet filter on the carb, if it has one. Check timing on your new to you motor. I would suggest you check compression so you know what you are starting with. Look at belts and power steering fluid quality, not just levels. Check the quality and level of the trim fluid. I'd probably replace both of those before running a new to me boat. Jump up and down on the drive and see if there is any give at all in the drive to transom. Should be solid as a rock with 2 people doing their best to force it to break off. (you can't hurt it)

 

[Cecil Diesel]

When rebuilding the carb do you know if the carb rebuild kits come with what adjustments you need to set on the carb? I know I can rebuild it but I want to make sure the carb is adjusted correctly.

 

[alldodge]

They usually do, if you get one which doesn't post here and we can get them for you. Can also go to boatinfo in Ricks posting above and look up manual 41

 

[Cecil Diesel]

Update: I rebuilt the carb and it was pretty dirty. So I took it out for a test run last night and the boat did preform better but it is still stalling out at about 2900 RPM with a WOT. I took the boat back home and decided to look at the distributor cap and when I did I noticed some green growth on the points. I am now waiting on delivery of a new distributor cap and rotor. I am also going to change the spark plugs and wires.

My question is do you think this could be the issue or is it fuel related? The boat in neutral will come up to full RPM no problem, but when you put it in gear and try to go it stalls.

 

[alldodge]

Reving in neutral doesn't mean much, and I still think you have a fuel problem

 

[Cecil Diesel]

alldodge do you thing it could be old fuel possibly? I have changed the inlet filter and the water separator filter. The only thing left in the fuel path is the fuel pump.

 

[alldodge]

It could be old fuel, not enough BTU's
Add new fuel to old in most cases just makes more old fuel

Everything for me points to motor is not getting enough fuel, but if the fuel is bad, then this could also cause the issues

 

[Cecil Diesel]

Update: Added about 10 gallons of new 93 octane fuel, cleaned the distributor cap and new spark plugs. It ran like it was brand new. My first assumption is that I had a couple issues, the carburetor needed rebuilt and the distributor cap had some corrosion on the points. I have a new distributor cap ordered and will put it on once it get here. I am going to take it out on Friday to test run it again, before we head to the lake for a week vacation.

Thanks everyone for the advice.