4.3 TKS "Run On" fixed but Slight Loss in Performance

[pbruley1116]

I have a 2010 Mercruiser 4.3 TKS with Alpha Sterndrive V6 with 2 BBL Carb and Thunderbolt V Ignition (Engine s/n 1A612644) that has problems with run on.

I read through Mercrusier Service Bulletin 97-17 "Engine Dieseling or Running-On" and have made the following changes to my set up in this order:
- Installed NGK TR6 Colder Spark Plugs gapped to 0.045 (still ran on)
- Installed a 140 DegF Thermostat (still ran on)
- Lowered the idle (this was the last thing I did and has fixed the run-on problem)

After making these changes I am grateful the run-on has stopped but I feel I have taken a little bit of a performance loss. Does running a colder thermostat lower engine power? The one I pulled was 160 DegF. Or could it be the plugs? The plugs I pulled were original OEM AC Delco AC 41-101 Iridium gapped to 0.060

 

[Bt Doctur]

Did you remove the cap on the idle mixture screw?

 

[pbruley1116]

Did you remove the cap on the idle mixture screw?

No
I did not touch the mixture screw on the carb.
I just backed off the "idle speed screw" ("A" in picture below) on the linkage to lower the idle RPMs

 

[Bt Doctur]

a very lean mixture setting will do the same thing , get the special tool, or cut it off, grind it off, etc and open the mixture up

 

[alldodge]

Lowering the idle rpm is what fixed the run-on
Everything else you did hurt performance

 

[pbruley1116]

a very lean mixture setting will do the same thing , get the special tool, or cut it off, grind it off, etc and open the mixture up

Just to be clear .. my boat runs great and even turns off now when I want it off. There is no more run-on issue. I am asking if the changes I made would reduce my performance.

The performance loss I am experiencing since changing plugs/thermostat i is very minimal but noticeable:
-Boat does not accelerate as hard as it used to and
-my top speed is slower by 3-4 miles per hour

I did not touch the mixture setting so explain to me how screwing with the mixture setting is going to bring back the little bit of power I have lost since changing plugs/thermostat ?

 

[pbruley1116]

Lowering the idle rpm is what fixed the run-on
Everything else you did hurt performance

Yes this is what I am thinking.
I am leaning toward the thermostat as the culprit... as plugs basically all do the same thing. But I am looking for someone with experience to weigh in to verify.

 

[nola mike]

If running a hotter stat and plugs gave you the equivalent of 50 hp, I'd be the first one in line at the parts counter.
Switch plugs back first, see if it changes, switch T-stat next, see if it changes...

 

[alldodge]

.045 gap to .060 ignites all the gas faster, that's why plugs installed are colder

 

[Rick Stephens]

.045 gap to .060 ignites all the gas faster, that's why plugs installed are colder

I don't get your meaning here. Not arguing, just not understanding.

He switched to iridium plugs, which would require the .060 gap. I believe.

 

[pbruley1116]

I don't get your meaning here. Not arguing, just not understanding.

He switched to iridium plugs, which would require the .060 gap. I believe.

No I switched from iridium to standard plugs

 

[pbruley1116]

Pulled the Original Factory Installed spark plugs and found AC DELCO p/n 41-101 The plugs look fouled with black carbon from running too hot/lean
These plugs have the following attributes:
Iridium
Heat Range =4
4k-7.5k ohms resistor
Gap 0.060
Socket 5/8 (16mm)
Reach 0.68 in (17.5mm) short reach (measure this with caliper)
Thread 14mm

 

[pbruley1116]

I installed NGK TR6 Nickel plugs
they came factory gapped to 0.039" but I regapped them to 0.045
per Mercury Service Manual #25 for GM V-6 262 CID (4.5L)

 

[QBhoy]

No I switched from iridium to standard plugs

Not sure these call for iridium plugs originally. Also not sure you can or are meant to gap those either.
Speed is easily lost or gained by many many things, as you’ll know. Especially if you are using the dash speedo for speed. I can lose 5-7 mph having more fuel…an extra passenger, having the camper hood up…or I can even gain dash pitot speed by trimming down from optimum trim position (meaning the boat is actually running slower gps, but the pitot is picking up more water pressure and showing faster at the gauge !)

 

[pbruley1116]

Here is the sticker on the top of my engine
You can see Merc is calling for AC 41-101 Iridium plugs gapped to 0.060
This is what they installed at the factory in 2010

 

[pbruley1116]

And here is a picture of one of the plugs that were pulled
It is very black and carboned up and same model # as engine sticker

 

[QBhoy]

Here is the sticker on the top of my engine
You can see Merc is calling for AC 41-101 Iridium plugs gapped to 0.060
This is what they installed at the factory in 2010
View attachment 367190

Ah. That’s news to me. Every day is a school day. I knew the mpi version called for iridium. But not the carb. Certainly the older carbs were all br6 variants. Didn’t know the tks newer models called for these. Can’t think why. Someone who knows more than I will answer that perhaps.
It’s definitely a tks ? Fair play and always happy to be corrected!

 

[pbruley1116]

Speed is easily lost or gained by many many things, as you’ll know. Especially if you are using the dash speedo for speed. I can lose 5-7 mph having more fuel…an extra passenger, having the camper hood up…or I can even gain dash pitot speed by trimming down from optimum trim position (meaning the boat is actually running slower gps, but the pitot is picking up more water pressure and showing faster at the gauge !)

You are absolutely correct
It might be no significant change at all ... just my imagination .... and yes I was using the pitot tube speedometer.

 

[pbruley1116]

It’s definitely a tks ?

Yes

 

[QBhoy]

Yes
View attachment 367192

Fair play ! I’d have a few more trial runs to see how she goes perhaps. Like you’ll know…speed can wildly vary between attempts.