Mercruiser 3.0 TKS Studder coming off plane

[Mercruisermike85]

hey guys this is my first post. Bought this boat back in 5/17. It’s a 2009 bayliner 175 w/ mercruiser 3.0 with the TKS carb serial# 1A337012 Boat has ran pretty good until Presidents’ Day weekend where I took it out and it started fine went thru no wake and went to give it gas and it would stumble. Replaced spark plugs,plug wires,antisiphon valve, cap and rotor. Ran it again and boat ran pretty good for 2.5 hours then coming back in it would stumble then I’d let off the gas the idle went really low and wanted to die and eventually did. Restarted after about 10-15 minutes and got back to the dock. I did however notice that I bought champion spark plugs with a heat range of 12 vs the oem ac delco which has a heat range of 3. So I took the champions RS12YC out and put brand new ac delco mr43lts back in it. Haven’t water tested it yet. I can’t belive out of all the 3.0’s out there I’m the only one that used a champion cross reference. I know heat range is important but as far as I’m concerned that isn’t a cross reference plug. Anyone else have done this?also anyone think it could be possible that the carb is gooch’d?

 

[alldodge]

Its not the plugs, MR43LTS, RS12YC, BPR6EFS all the same heat range

Have you changed the fuel filter?
Check the fuel filter contents, pour in clear container see if there is something besides gas.
If gas is clear and filter is fuel check fuel pressure, should be 6 to 8 psi at 1000 rpm

Edit: changed 3 to 7 psi tp 4 to 8 psi at 1000 rpms

 

[Mercruisermike85]

I still need to do a fuel sample and yes I did replace the fuel filter along with the other things I mentioned. I also should mention that the idle seems a bit high around 850-900 warm in the water. I could of swore when I pulled up the info on the plugs the champion was a hot plug and the ac was a cold plug

 

[Maclin]

Sounds like the carb fuel bowl could be overfilling. Is there a strong smell of fuel when you open the engine compartment when this happens?

What did the Champions look like.

 

[alldodge]

There is a procedure to adjust idle but it is done in gear and adjusted to 650-700 rpm. The 900 does seam a bit high in neutral so may need adjusting, or timing needs to be checked. Would guess timing should be set 2 ATDC being a 2009, but would need your serial number to verify (0L43100 and higher)

 

[Scott Danforth]

My guess is crud in the fuel system. May need a carb rebuild

 

[Mercruisermike85]

[No message]

 

[Mercruisermike85]

Fuel checked out fine not a drop of water in it. If you guys think the carb needs to be rebuilt, has anyone ever just done a swap from marinecarburetor.com? Seems like a good deal

 

[alldodge]

Look good IMO, except the right one may have some oil leaking in from a valve guide or seal

 

[Mercruisermike85]

Yeah on my old ac delco I pulled out it was like that to from cylinder #2 trying to upload a picture but it says it’s too big.. should I run a compression test?

 

[alldodge]

should I run a compression test?

Would not hurt, but if its a valve seal, it may not show much if any difference

In any case I don't see this as your current issue

 

[Mercruisermike85]

Yeah I don’t know if I forgot to mention that this only happens when the motor has been ran for at least an hour

 

[alldodge]

Yeah I don’t know if I forgot to mention that this only happens when the motor has been ran for at least an hour

Might be the antisiphone valve or the vent valve

The antisiphone valve can get clogged a bit and make the fuel pump work harder, but if the vent valve is clogging then the tank starts to draw a vacuum. If its the vent, when it does it, open the gas cap and listen for air to get sucked in

 

[Mercruisermike85]

Anti siphon valve replaced and vent I blew some nitrogen thru nothing came out and is clear :-/

 

[alldodge]

Anti siphon valve replaced and vent I blew some nitrogen thru nothing came out and is clear :-/

Has anything else been done so we can have a clearer pic of the status prior to leading up to current issues?

If nothing else, suggest putting a pressure gauge on the fuel line

 

[Mercruisermike85]

The list of what I’ve done is

new plugs(twice now and gapped at .45)
new carb inlet screen
new cap and rotor
new plug wires
oil change
anti siphon valve
nee fuel filter

noticed the week in between Christmas and New Years when I first went to give it gas out of no wake it hiccuped and I let off off the throttle but caught it’s self and it ran great the rest of the day. Took it out Presidents’ Day and that’s when it started acting up. So I did the tune up. Ran it the day after st Patrick’s day for 3 hours hard to check everything and it seemed fine until about the last 30 minutes coming back in letting off the throttle it stumbled and idled down real low and wanted to die and eventually did. Tried restarted and would restart unless I have it 50%+ throttle and it would still run rough at low throttle above 1200 rpm-2200 rpm

 

[Mercruisermike85]

Ok here is the list of what I’ve done

*new plugs twice first with champions now with ac delco (gapped at .45)
*New antisiphone valve
*new fuel filter
*new carb inlet screen
*new plug wires
*new cap and rotor-cap points had corrosion

I took it out 12/28 went thru no wake about 10 mins worth and gave it gas and it stumbled real quick so I let off and it caught its self and ran great the rest of the day. Took it out Presidents’ Day and it started and idled great cold went they 10 minutes of no wake again and now it wouldn’t go above 1,500 rpm so I was able to get it to 1,000 rpm back to the dock and that’s when I did the tune up. Took it out for a test ride for about a 45 minutes and it ran good. Took it out the day after st Patrick’s day and ran great for 3 hours and began stumbling coming off plane around 2000 rpm and idled real low and eventually died and only would restart with 50% throttle. Able to limp back to the dock again. Adjusted the plug gap from .35 to .45 and took it out last week and it ran for about an hour ok then started again. So that’s when I started researching heat range on the spark plugs. Took out the champions and now have a new set of ac delco

 

[Mercruisermike85]

Clearly I didn’t see that my first post went on a new page

 

[alldodge]

eventually died. Tried restarted and would restart unless I have it 50%+ throttle and it would still run rough at low throttle above 1200 rpm-2200 rpm

Maclin might have your issue with it flooding. If its flooding then keeping the rpms up helps burn the excess fuel off and it might not die.

Gap is .035

 

[Mercruisermike85]

The specs on the flame arrestor called for .45 gap

he maybe right about flooding because it does seem to be running rich when it happens, is that a carb issue?