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The "Admiral" is getting annoyed..

sandkicker

sandkicker

Outstanding Contributor
Background...
Factory new (mid summer 05) FWC 260 HP Merc 5.7 MIE (TKS carb) ran fine mid summer last year and then one day last September, it suddenly started to stumble at very low throttle openings. What I've done since then ( this has been posted here before)
Last year...
1) removed fuel filter ( Merc w/water separator)... drained it ( no water) refilled it with seafoam and ran the engine.
2) New plugs, cap, rotor (from the auto store)
3) cleaned carb
4) Found a metal shaving that drifts in and out of the gap between the idle mixture screw and the body of the carb. Removed it.
5) Triple checked firing order
6) retimed engine in base mode, reset idle.

Still no joy... pulled boat out for the season

This year
1) New cap, rotor (Mercruiser)
2) retimed in base mode.
3) reset float level to numbers in the book (never been changed before)... it was almost 3/16 of an inch off (high as I recall) on both numbers!
4) bought mixture adj tool and put engine in base mode at 650. Screwing the adjustment in does seem at one point to make the engine run rougher, however, backing it out past the point where is stops misbehaving (about 1/4 turn) has no apparent further result.

Further refined troubleshooting reveled that with the engine running at 650 rpm in normal mode, opening the throttle (at the carb with the cable disconnected) ANY amount causes the engine to stumble and stall dead.
If I reconnect the throttle cable and shift it into gear, it goes into gear and will idle, in gear, however...any small throttle increase in gear (or out for that matter) and it stalls.
If I "goose" it, everything's fine ( in or out of gear)... it revs up OK. HOWEVER... with a 2 ton boat and a 15x21 prop..."goosing it" when you first get into gear to keep it from stalling has potentially "amusing" results, especially when docking ( stern in to a bulkhead).

5) replaced the accelerator pump ( I called my brother in law who has a carry permit to accompany me to the dealer to pick up this part that apparently is worth half its weight in gold at $60+)... just kidding but for crying out loud $60!!!!... same result
6) Tried all three settings on the accelerator pump arm.
7) Shut fuel valve off, restarted engine and opened the throttle several times...engine stalled every time regardless of fuel level in the bowl, so its not likely a float level problem.

No joy... It got dark and I called it quits.

Boat has been in the water since early June and not out of it's slip. Per the title of the post... The "Admiral" getting unhappy.

Other observations...
When in base timing mode, idle RPM tends to "hunt" .... but not like the "normal" hunt from a hot cam, i.e., fast pickup, fast slow... it seems to be more of a wander.

Oh yeah.... fresh gas... tank pumped dry in spring and refilled with mid range gas (engine uses regular gas)

Idle RPM is also not stable ( as in its not always the same rpms) and as far as I can see would be more stable if the throttle arm had a return spring (if I push on the arm at the carb, it behaves). But this really has no bearing on the problem that I can see.

I'm starting to run out of ideas and tomorrow I'm planning to give the engine another shot of seafoam , for no good reason, since I started with that last season when the problem first cropped up and had the carb 99% apart and cleaned this spring. I have another set of plugs (platinum), but this problem started with the factory original platinum ( with less than 50 hours on them) and there is a non platinum set in there now with about 2 hours total ( less than 1 hour with the boat moving) on them.

As it is now, the boat is almost impossible to dock in the marine that its in. Unless you put it in neutral, coast up and hope you get close enough to snag a line with a boat hook. (boat does about 4 knots at idle). Docking it under power is a "tap...tap" in/out of gear kind of thing when the engine behaves... now... it's "dummy docking" only.

Any suggestions? I'm not a fan of the shotgun troubleshooting method... but I've run out of ideas except another set of plugs and a compression test... and I don't see that being other than a waste of time, however...!

Sorry for the long post...:(
 
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This is not what you want to hear, But so far I have been in your situation about 3 or 4 times now with those TKS carbs, And so far the only fix for me was new carbs under warranty.:(

Next time you run it, With the engine running unhook the big hose between the carb and the valve cover, What I have noticed is, if the engine is running right/Normal the engine will die if you unhook that hose, But if the engine is running like the way yours is, then the engine will rev up to a higher RPM on its own, I forget how high it goes up to right now, Its been a little while, But it should go up on yours if its doing the same thing that I have seen in the past.

Most likely your wasting time and money with new plugs, ect.

Try adjusting the engine speed and air/fuel mixture without going into base timing mode, Just to see what happens.

Good luck with it.
 
4) Found a metal shaving that drifts in and out of the gap between the idle mixture screw and the body of the carb. Removed it.
Click to expand...

4) bought mixture adj tool and put engine in base mode at 650. Screwing the adjustment in does seem at one point to make the engine run rougher, however, backing it out past the point where is stops misbehaving (about 1/4 turn) has no apparent further result.
Click to expand...

Damaged needle seat? Replace the carb as Boat Tech states.
 
re: "Damaged needle seat? Replace the carb as Boat Tech states."

I inspected the seat under magnification when I cleaned it, and the seat at the point that it meets the carb bore is clean and free of dings. The metal shaving looked like a chip that did not get removed from the tapping operation of the needle bore and came adrift.

Re: "need a new carb".... I find it hard to believe that there is a failure mode on this carb that requires its complete replacement that goes like this:

1) Boat runs great... spend couple hours drift fishing in the bay with the wife, repeatedly starting engine and jockeying for position over structure.
2) Tide goes to slack and decide to leave for home
3) Cruise home at 2600 RPM (a lazy day and in no big hurry to get home)
4) About 20 mins later, see what looks like a school of blues harassing bait fish on top...
5) Put in Neutral to approach fish... idles OK
6) Put in gear... idles OK
7) open throttle slightly to more closer... engine stalls.
Think "maybe vapor lock??"
8) Restart engine... same symptoms. Docking was "fun".

I've got a sick feeling that I need to run a compression check as this can all be explained (sigh) by a leaky/burned intake valve... or a bad wire.
Let me get these possibilities out of the way.

I'll try "Boat_tech's" test re the valve cover vent hose.
 
Check for a vacuum leak around the carb base and the intake. Spray a little WD-40 around the gaskets. If RPMs increase; you found the leak. I set the idle mixture w/a vacuum gauge. Look for a port plug on the intake man. near the carb. Remove it and install a nipple for the gauge. Tune the mixture screw in/out for the most vacuum on a warm engine.
 
"I find it hard to believe that there is a failure mode on this carb that requires its complete replacement that goes like this"

Does the Admiral want to go boating or keep getting frustrated? Reading your first post my first thought was try getting a new carb or take yours in and have it professionally rebuilt. If boat_tech has gone through this experience before and he had to install a new carb then that's probably your answer. If there is another better carb that will work on your engine you might try that from the sounds of it.
 
Since the engine/carb has less than 40 hrs on it, not feeling the need for a rebuild.
I did however manage to get the problem 99% fixed, at least to the point where I feel that tweeking the idle mixture wll 100% fix it.

As the engine now stands, with what I call a "Ghetto fix"... Open throttle slowly (out of gear)... no longer stalls. Open throttle slowly in gear... runs rough at the point it used to stall...hence my comment about mixture.

Sooo....what broke on the carb and what did I do to fix it???
Actually NOTHING BROKE... what went wrong? Well, when I took the top off the carb the last time, I chipped/scraped the PAINT off of the accelerator linkage pivot (that which has the retained clip on it. When I did this, I destroyed the "zero clearance" bushing that the paint on the throttle linkage made with the link to the accelerator pump. This allowed just enough "slop" so that the accelerator pump didn't do it's thing when the throttle first started to open. What also made it worse, is that the top of the accelerator pump link rod where it attaches to the rocker on the carb that actuates the pump is a bent rod and with minimal age and the loss of the paint "zero clearance bushing" at that point, that rod slides down the radius slightly when the throttle actuates. This is yet a second point of slop.

The "Ghetto fix"... a rubber band judiciously placed to take all the slop out of the system.
A short bungee cord fixed the wandering idle problem as well... so that's two ghetto fixes.

This weekend going to the hardware store for some S/S springs and some aluminum for brackets.

First job I ever had was in a radio/TV repair shop while I was in H/S, the owner taught me..."If you can't fix it, modify it!"
 
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sounds to me a the idle circuit is clogged, you want to jury rig it ok i do it all the time.

Or maybe water ion the bottom of the bowl.
 
just guessing, but this being a TKS carb, think they have an IAC circuit, was that checked at all, could cause those symptoms?
 
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