4.3 Carb Engine "Run On"

[racer2c]

Spent six awesome hours on the lake today wakeboarding, tubing, running around. One time though I turned the key off and the engine kept sputtering along for about 30 seconds until it finally stopped. I use to have an old Dodge in high school that did that too. :?

It didn't do it again all afternoon. Anyone else have this happen?

Also, starting and stopping the engine all day long to switch wakeboarders, anchor etc, how long does a starter typically last on the 4.3?

[seapuppy]

it's called dieseling and it can injest water when the engine runs like that.....damage can be done doing that called hydroloc....so...the best thing to do is let it idle for a few minutes and then make sure your idle is set properly...somewhere around 600-650rpms.....you have to also make sure your timing and dwell on points is correct if points are installed on your engine.....if you have electronic ignition..then ignore that part....dieseling can also be from too rich a mixture on the carb....if your good with carbs...adjust the idle mixture to proper setting ...all those can affect dieseling....

welcome to the zoo....

[racer2c]

Thanks! When the kids are wakeboarding/tubing I'm starting and stopping the engine so much, I attributed the diesling to that. It's a new engine (I've put it's first five hours on it this week) so maybe a carb adjustment is in order?

[Brit Rider]

Hey Racer,

I had that problme before on a 4.3 carb, as have many.

Its a pain in the ass to fix and we tried for so long.. then just gave up!
Best thing to do as seapuppy suggested is to let it run for 30 secs or so after your set.. then shut it down.

The 4.3 V6 Carb is notorious for this problem and all i can tell you is that its not the spark plugs, timing or carb. Some people can fix it by adjusting the idle but some engines don't respond well to that.. seems to depend on how bad it is. It'll only happen when its been run relatively hard and when quite hot.

This is why I went to the MPI this year, last year was the first year I used Fuel injection (Super Air Nautique with 5.7 EFI) and now i won't look back.

Hope that helps a little

[racer2c]

Hey Racer,

I had that problme before on a 4.3 carb, as have many.

Its a pain in the ass to fix and we tried for so long.. then just gave up!
Best thing to do as seapuppy suggested is to let it run for 30 secs or so after your set.. then shut it down.

The 4.3 V6 Carb is notorious for this problem and all i can tell you is that its not the spark plugs, timing or carb. Some people can fix it by adjusting the idle but some engines don't respond well to that.. seems to depend on how bad it is. It'll only happen when its been run relatively hard and when quite hot.

This is why I went to the MPI this year, last year was the first year I used Fuel injection (Super Air Nautique with 5.7 EFI) and now i won't look back.

Hope that helps a little

It helps a lot! Thanks! Know anyone who wants to buy a slightly used 1800-SR3 carbed? :wink:

[racer2c]

B-R what do you think about dropping to a 140 degree thermo? I've been 'googling' the dieseling issue and many say they resolved by either dropping to a 140 (which they claim is a Merc recommendation) and/or using octane booster or premium gas. I've also seen mention of a Mercruiser "idle stop" kit.

[seapuppy]

what you need to do is a couple of things...one..change the thermostat to 140 degs....then change the plugs one step colder....the last thing is to adjust carb idle circuit by setting the jet settings all the way in and then turning them out 1.5 turns..start the engine .and turn out 1/4 turn let sit for a few minutes and see if it settles down and smooths out....then 1/4 turn more....each time you adjust the jet...let it settle and see if it idles smooth...when that happens..it's done...adjust the idle speed setting to 650 rpm...that should do it........but with only 5 hrs of engine time...you haven't even broken it in yet...do all of this at 20 hrs...for now let it idle for about a minute or two before you shut it down.....let the engine cool...all the tolerances are still tight....alot of heat is in there......

[racer2c]

what you need to do is a couple of things...one..change the thermostat to 140 degs....then change the plugs one step colder....the last thing is to adjust carb idle circuit by setting the jet settings all the way in and then turning them out 1.5 turns..start the engine .and turn out 1/4 turn let sit for a few minutes and see if it settles down and smooths out....then 1/4 turn more....each time you adjust the jet...let it settle and see if it idles smooth...when that happens..it's done...adjust the idle speed setting to 650 rpm...that should do it........but with only 5 hrs of engine time...you haven't even broken it in yet...do all of this at 20 hrs...for now let it idle for about a minute or two before you shut it down.....let the engine cool...all the tolerances are still tight....alot of heat is in there......

Very cool! thanks Seapuppy!

[Brit Rider]

I've also heard that a thermostat change helps a lot.


what you need to do is a couple of things...one..change the thermostat to 140 degs....then change the plugs one step colder....the last thing is to adjust carb idle circuit by setting the jet settings all the way in and then turning them out 1.5 turns..start the engine .and turn out 1/4 turn let sit for a few minutes and see if it settles down and smooths out....then 1/4 turn more....each time you adjust the jet...let it settle and see if it idles smooth...when that happens..it's done...adjust the idle speed setting to 650 rpm...that should do it........but with only 5 hrs of engine time...you haven't even broken it in yet...do all of this at 20 hrs...for now let it idle for about a minute or two before you shut it down.....let the engine cool...all the tolerances are still tight....alot of heat is in there...... Sea puppy... you clearly know a lot more about engines than me so i'm just going to nod and say "unhuh,, what he said" but your instructions do seem to make good sense. though I'd really consider taking it to the dealer to have that amount of work carried out. just incase you lose your place on the carb settings etc... and you migh be able to swing the pugs, thermostat etc.. as warranty ;)

[seapuppy]

BR...good point...I was assuming it was out of warranty or my 2 braincells farted....either way if it's under warranty...take it to the dealer and scream bloody murder that it diesels....(jk)...but do let them know....what I didn't tell you to do was if you turn one idle jet out...you have to do both at the same time...ie one jet then the other the exact same amount.......

BR...I used to build and race different engines...one thing I seemed to like to mess with was carb's.....webber side draft and 48ida's were easy to me..I can rebuild those in my sleep........hemmingways....hope this helps......

[3388sam]

FYI- The carb. bases on Merc. engines are often plugged so you do not have access to the idle air screws.
It's under warranty have them fix it for you, if you remove the plugs (no easy task in it's self) it could void your warranty

#25 is the screw you are looking for!

http://media.stemtostern.com/LSDATA/LSDATA_FULL/CRUISER/17468/23.GIF