I6 Merc idle problem after cruising

Well, I got to take the boat out today for a couple of hours to see how she runs after a carb rebuild. From previous problems that needed attention when I bought the boat (84 Checkmate Enticer with a 83 115hp Merc) I replaced the stator and rectifier, new floats and carb kits for all 3 carbs, removed the idle stabilizer, inserted the BB in the small tube above each carb, set my max timing to 23 deg with midgrade fuel and good oil, and replaced quite a few bad wires on the motor. I had done the linc and sync once and again after I rebuilt the carbs as recommended from a link that is provided around here. The carbs were dripping fuel out the throats and dripping fuel into the water but that seems fine now after the rebuild.

So the problem is that after running the engine at cruise speed for a while and returning it to idle it will idle great for about a minute then start to "load up" and die. I did play with the idle mixture screws out on the water and it didn't matter if I turned them a little rich or lean it would still stumble and die. The choke works fine. It's the keyed pushbutton and it starts great cold. It will cause a stumble in the engine if I push it when it's warm....so I believe it's working properly (and not leaking when it shouldn't). Have you guys had and issues with fuel pumps or diaphrams causing idle issues? I did go back and squeeze the bulb when I was having problems and it was hard. Can a fuel pump diaphram have a pinhole in it that would let the engine run rich at idle?

I suppose I could take apart the carbs again but their pretty darn simple. Float level was easy to set and all jets and passages were cleaned and blown out...so I don't really think it's in the carbs. I have now done any service to the fuel pump yet besides check the inlet screen.

I'm going to go pull the spark plugs and inspect them. Check back later.

Re: I6 Merc idle problem after cruising

decarb


and anything is possible

50-1 mix? tcw-3 oil?



merc don't like to idle. keep it at 1k+ when going slow. just want it slow to shift.

Re: I6 Merc idle problem after cruising

Yes on the mix, yes on the oil. I set the idle to 800rpm in gear on the muffs. I understand it doesn't have to idle down to 600 rpm but I don't want it to bang gears at 1000rpm. After cruising it would idle in gear at 750rpm and then start to load up and die.

The spark plugs looked all the same, oily. Too bad it was a long fast idle back to the dock from a full throttle run that probably made them look that way. Engine looks very clean now. No more
spitting from the carbs and fuel all over the place though. Just for sh*ts and giggles my son helped me do a compression test and it was 127 to 134 on all cylinders.

There was some residual fuel/oil around the fuel pump gaskets. In my previous post I meant to say that I had not done any service to the fuel pump since I have owned this motor.

Prolly should do a fuel pump pressure and vacum test but for under 10 bucks I can replace with a fuel pump diaphram kit.

Thing thats wierd to me is that out on the water the motor didn't respond well to either richening all idle mixture screws a 1/4 turn OR leaning them 1/4 turn when it does this. Either way it wanted to load up and die.

Re: I6 Merc idle problem after cruising

keep the needles on the rich side. they like fuel. trust me

idle sounds about right i guess. my motor likes 480 sometimes but that's too low.

i just found your mistake

every adjustment should be when the motor is underload. that means setting the idle in the WATER. on the muffs it has no back preasure and is totally different in the water. from what it sounds like is that your idle is too low.

mine will do the same thing if it's too low.

again you want it low enough to shift and idle in gear for a little. but keep it at 1k just for cruising slow.

Re: I6 Merc idle problem after cruising

Yeah, I know what your saying. Just thinking to myself going through that whole process and making the final adjustment on the throttle cable out on the water might be a bit much. Might be best to do that still hooked up to the trailer before cutting it loose!

I'm running 6 deg's ATDC per specs (5-7) at idle. With the idle stabilizer removed do you or anyone else run a little more advance at idle?

Thanks

Re: I6 Merc idle problem after cruising

i don't know what the idle ATDC or idle stabilizer since all i have to work on is old motors


all i can help is maybe the fuel.

i would try it without the idle stabil and set the ATDC thing your talking about at factory spec. they give you a range so what ever you feel is right in that range.

since this is ATDC wouldnt it be better to have a smaller number to raise rpms? i have no clue though

i would do a decarb first off. all it can do is help