Rough running and stalling at idle speed - disconnect TKS helps

[blued]

I had the boat at the lake over the weekend and a problem developed on the first day where it got really lumpy while at idle both in and out of gear. Then on day 2 it got worse to the point where it would cut out and be quite difficult to start. This is the first time out since I serviced it so we inspected the fuel filter for leaks and all the lines but couldn't see any issues. After the boat sat for 30 mins it seemed to idle OK for the first 20 mins or so but then after some skiing went back to being lumpy and stalling.

It felt like it was running rich or a choke sticking open is the best way I can think to describe it. There doesn't appear to be an accessible mixture screw on the carb so I tried disconnecting the connection to (what I assume is) the TKS. After this the engine didn't stall again but I could still feel it running lumpy around 1200rpm when picking up a skier. With the TKS disconnected it was harder to start than normal and idled high at around 1000rpm.

The boat was running perfectly otherwise, right through the rev range anywhere above 1500rpm.

Can anyone point me in the direction of a fault finding manual for TKS on the 3.0? I've found one for testing the TKS Diode on the 4.3 and up but I think these are all MPI?

If there is somewhere else I should be looking please let me know, I'm starting with TKS because it didn't stall the rest of the day or the following day with it disconnected. Although I did reconnect it to start the engine first thing in the morning on day 3.

 

[blued]

I did some digging and found this thread -

http://forums.iboats.com/forum/engi...inboards/648904-how-does-tks-work-technically

The symptoms I'm seeing suggest the TKS isn't preventing enrichment, by deploying the plunger, when the engine is warm. I'm not sure why disconnecting it stops the engine from stalling, if I've read the details in the thread correctly it should do the opposite?

"The TKS fuel / air passage is normally open, allowing fuel enrichment mixture through the
carburetor continuously, unless the passage is blocked by the plunger of the TKS module.
With the key switch in the start position, the vacuum of the engine pulls the enrichment fuel
and air into the intake manifold.This starts an electrical warming of the module.
With the circuit completed, the electrothermal TKS module brass plunger extends to block
the enrichment passage."

I'll head over to the boat tomorrow and do the following:

- check there is voltage to the TKS module
- start the engine and wait 6 - 10 mins and see if the TKS module gets warm
- check to see if the hissing stops after 10 mins

I think I should have a better idea then if the TKS is a factor.

Please feel free to throw in any other ideas if I've missed anything.

 

[Scott Danforth]

Sounds like crud in the idle circuits, rebuild your carb and check your fuel filter for water

 

[alldodge]

Agree clean your carb and here is the manual

http://boatinfo.no/lib/mercruiser/manuals/mercruiser41.html#/0

 

[blued]

I checked my filter for water but the fuel was good, nice and clean. Started the engine and it ran fine until a few seconds after the TKS hissing stopped and then it stalled. Next I removed the flame arrester and had a look in the carb, there are some deposits in there so I pulled it off and pumped the fuel into a jar. There didn't appear to be any water in there either although it was a little cloudy.

I'll try to get a kit tomorrow, is it a straight forward rebuild? I've only every done a rebuild on a 2 stroke jetski carb and from looking at a few diagrams there are more components in this one!

Also how do I clean it? Will soaking it in carb cleaner be sufficient? How long for? I've only ever seen it in spray cans so will need to see what else is available.

 

[achris]

...Can anyone point me in the direction of a fault finding manual for TKS on the 3.0? .....

TKS manual.

 

[Senior B]

TKS is ok when it works. The solenoid on the back of the carb is a replaceable part by it-self. I worked on a boat for a friend that had TKS carb and his problems were the same as yours. He just got me the entire carb and I had it swapped out in 15 min. Boat has been perfect since then. The solenoid is very easy to swap out but I found the carb it-self not so easy to mess with. Good luck.

 

[blued]

I stripped, cleaned (as best I could without a dip) and rebuilt the carb on Wednesday and refitted the next day. I set the idle speed screw to default, ran the engine up to temp and adjusted to about 800rpm. It sat running perfectly in the boat yard and also ran perfectly on the water. However after I'd been out for about an hour it started idling high at 1100rpm or so. I've adjusted it down to 800rpm again but haven't had the chance to do another cold start. I suspect it might stall after the TKS stops the fuel enrichment - if this is the case is there something else I can check while I'm over there?

 

[Scott Danforth]

Did you run a fine wire thru every circuit passage?

 

[achris]

What about a vacuum leak somewhere in the manifold/gasket? That would fit the symptoms quite nicely. You familiar with finding vacuum leaks?

Chris........

 

[blued]

Did you run a fine wire thru every circuit passage?

No because the manual specifically says not to use wire in jet passages or tubes because it can cause damage.

 

[blued]

What about a vacuum leak somewhere in the manifold/gasket? That would fit the symptoms quite nicely. You familiar with finding vacuum leaks?

Chris........

I checked for leaks on a car a long time ago, from memory I need to spray something like WD40 and listen for a change in the engine? Is it just where the carb bolts on to the manifold I need to check?

 

[achris]

Where the carb bolts to the manifold, where the manifold bolts to the head, and any plugs in the manifold and inlet side of the head.

 

[Scott Danforth]

No because the manual specifically says not to use wire in jet passages or tubes because it can cause damage.

I know what the manual says, I also know that unless you are 100% positive every circuit passage is clear, you really didnt clean the carb.

how much crud did you find in the bottom of the bowl?

 

[blued]

I know what the manual says, I also know that unless you are 100% positive every circuit passage is clear, you really didnt clean the carb.

how much crud did you find in the bottom of the bowl?

I just followed the instructions because I hadn't done one before, didn't want to risk damaging something.

The bowl was pretty clean, nothing floating about, just a small spot of corrosion on the edge of the cylinder the throttle plunger sits in.

 

[Senior B]

On the site Boatinfo.com, there is the factory Merc Manual for the TKS carb that is free to look at. Believe the problem your experiencing with the high idle is because you set the idle speed too soon before the engine was completely warmed up and set it to high at 800 rpm. Set it again when it's at it highest point and set it down to 650 rpm. The TKS book is well written and explains well how this "smart carb" is supposed to work.