mercuiser 888 wont idle below 1000 rpm

[mauro.]

Hello there I have a Mercruiser 888 that I just put into the boat that I bought recently
the problem is that it wont idle below 1000 rpm and also it is getting to high temprature around 80 decrees celcius
thanks in advance
Mauro

 

[alldodge]

Start by checking compression to verify health of the motor, should be close to 10 Bar. Highest and lowest cylinder pressure should be within 10%

Next get into the carburetor, most likely the idle circuits are clogged

 

[Scott Danforth]

for the temperature.

start with pulling the drive and replacing the raw water pump. if your impeller is missing fins, go thru the system until you find all the parts.

you should be about 65-68C with a raw water cooled motor

 

[nola mike]

Wow, didn't know both of you guys were bilingual!

 

[Scott Danforth]

Wow, didn't know both of you guys were bilingual!

And we get it right, not like NASA

I can even measure velocity in furlongs per fortnight

 

[mauro.]

The engine and boat were all rebuilt but sadly were left out in the weather as the guy who did that passed away and so when I bought it I had to tear out the engine and every thing to clean it form rust and every thing and now I have just put every thing back together ready for the water except for some fine tuning. Yes the compression is good and the carb rebuilt same for the distributor it is a new pertronix marine electronic dist but the timing hasent been set with a timing light so maybe that is of some truble? oh and also I replaced the water pump in the drive yesterday so it should not be a problem
thanks
Mauro

 

[mauro.]

oh and by the way the engine guns on a coolant circuit which gets cooled by the fresh water through one of those round radiators that are filled with little tubes that the water goes through

 

[alldodge]

Timing can cause the issue, but most cases it's the carb. When motor gets above 1000 it starts transitioning from the idle circuit to main jets.

Your motor uses a heat exchanger (HE)
In your first thread Bondo mentioned to replace the impeller and housing. If that was done, then need to find out if the pump is moving enough water thru the HE.

Connect a short piece of clear hose between the pump and thermostat housing. Boat should be in the water and look for bubbles

If flow is good, then there may be a head gasket leak or HE may need to be cleaned

 

[nola mike]

Did you set the mixture screws on the carb?

 

[mauro.]

yes the mixture screws are set but they don't seem to make a difference could float level affect idling? I replaced all the seals so the head gasked is out of the question but a plugged HE could be my issue

 

[mauro.]

and by the way just wondering does anyone of you guys now what the best timing advance curve is for the mercruiser 888 so I could tune up the dist as it came with three sets of different springs and a graph of the different curves one can make out of them
thank you all
Mauro

 

[Scott Danforth]

oh and by the way the engine guns on a coolant circuit which gets cooled by the fresh water through one of those round radiators that are filled with little tubes that the water goes through

so you have a fresh water cooling heat exchanger.

then there should be a 70C themostat vs the 60 with a raw water cooled motor

stick with stock curve from mercruiser. 20 degree advance. 4-6 degrees of base timing

however what you are describing is an automotive distributor.

 

[Scott06]

and by the way just wondering does anyone of you guys now what the best timing advance curve is for the mercruiser 888 so I could tune up the dist as it came with three sets of different springs and a graph of the different curves one can make out of them
thank you all
Mauro

is the throttle cable allowing the plates to close ? there is an adjustment on throttle cable. If you take throttle cable off can you turn the idle speed (not mixture) down

 

[mauro.]

so you have a fresh water cooling heat exchanger.

then there should be a 70C themostat vs the 60 with a raw water cooled motor

stick with stock curve from mercruiser. 20 degree advance. 4-6 degrees of base timing

however what you are describing is an automotive distributor.

it says marine on it so you would go a base timing of 6 instead of the 10 it says in the manual?

 

[mauro.]

the throtle cable is off if I close it it will die should it be compleatly closed at idle?

 

[kenny nunez]

You need to check that the”0” top dead center timing mark on the balancer and the timing pointer with #1 cylinder at top dead center are the same. It may be possible that the outer ring of the balancer has slipped.
When a Holley carburetor is correct the idle stop screw is around 1-1.5 turns and the mixture screws 1.5 turns from lightly seated. Anything other than that means there is a problem elseware.
As SD suggested stick with the stock ignition curve.
Are you sure that your engine has the correct firing order? 13726548. If it does not run right it could be someone swapped the cam for an automotive firing order. 15426378

 

[mauro.]

yes the mark alignes with tdc and I have the corect fiering order as I replaced the cam with a used mercuiser 888 cam as I round the dist gear

 

[mauro.]

do you have the graph of the curve?

 

[Scott06]

the throtle cable is off if I close it it will die should it be compleatly closed at idle?

there should be a idle speed adjust screw that sets idle speed. if this is missing or miss adjusted yes it will die.

shown in second pic in article

https://www.holley.com/blog/post/here_is_the_correct_procedure_for_setting_an_optimized_idle_mixture_and_speed/?srsltid=AfmBOoq0GkbAC0T2owwqmPG_NvcpA3z7YIGXrW3TgQDCmHS0UMxaCYt9

 

[mauro.]

there should be a idle speed adjust screw that sets idle speed. if this is missing or miss adjusted yes it will die.

shown in second pic in article

https://www.holley.com/blog/post/here_is_the_correct_procedure_for_setting_an_optimized_idle_mixture_and_speed/?srsltid=AfmBOoq0GkbAC0T2owwqmPG_NvcpA3z7YIGXrW3TgQDCmHS0UMxaCYt9

it does have an idle screw that I have put at 1and 1/2 turns in as soon as it started to oppen the buterflys