Don I've been thinking about my issue...

[macr6]

3.0L 98 mercruiser starting problem.

QUICK RECAP: Engine starts fine cold. idles fine with RPMS set to 700. When the boat has been run for a while and is up to operating temp it becomes hard to start and wont idle well.
http://forums.iboats.com/showthread.php?t=267264

You said to check the choke would be closed. However when I pull the flame arrestor the choke plate is wide open. However the engine is still hard to start. I can only start it by pumping or finding the sweet spot on the throttle lever. Once it does start at this point it is hard to keep it idling. Once I do get it started though I can get going with no problem.

I have been mulling this over all week and have been thinking that with the choke plate wide open and the throttle lever in nuetral that the butterfly plates or throttle body valves (not sure what they are called) are all the way closed and starving the engine of air. Is this right? Is this a "rich condition".

I am thinking the idle mixture screw and idle speed screw are not set right. I am trying to make an educated assumption with this and hope that I am close. The question is do I need to get the engine up to op temp to make adjustments? OR If it idles fine cold is it just the choke plate?

I will be heading down to the boat tomorrow to fix.

 

[JustJason]

Re: Don I've been thinking about my issue...

I'm no don.... But....

cold engine = choke plate closed
warm engines = choke plate open.....

and that's that.

as far as your hard starting issue.

When was the last time the motor had a full tune up?
Double check the base timing..... if its off just a few degrees it'll run ok but can be a bear to start.

dont worry about your mixture screws just yet.

on a warm engine the carb shouldn't need pumping, and pumping it to much is just going to flood it out.
carbs do however require manual input to start the engine, soooooo
the next time out, after the boat is warm, put the boat in neutral and push the throttle to about the 1/4 open position before you crank it, then crank it.

 

[macr6]

Re: Don I've been thinking about my issue...

I'm no don.... But....

cold engine = choke plate closed
warm engines = choke plate open.....

and that's that.

as far as your hard starting issue.

When was the last time the motor had a full tune up?
Double check the base timing..... if its off just a few degrees it'll run ok but can be a bear to start.

dont worry about your mixture screws just yet.

on a warm engine the carb shouldn't need pumping, and pumping it to much is just going to flood it out.
carbs do however require manual input to start the engine, soooooo
the next time out, after the boat is warm, put the boat in neutral and push the throttle to about the 1/4 open position before you crank it, then crank it.

That is exactly how I have to start the engine. I manually move the throttle lever to about 1/4 open just like you said. When the engine catches however it acts like it doesn't want to keep an idle.

I don't pump it (I may have mis spoke). I have to coax it to start. Almost feathering the throttle to find that spot where it will catch.

IF this is normal operating procedure then my only other problem is: when the engine has been run nice and good and is up to op temp and stopped; (Like when I am pulling a tube and want to change people out) once I get it started the engine has a hard time staying running. Rough idling. I have to get it started and almost immediately throttle up so it doesn't die.

 

[chiefalen]

Re: Don I've been thinking about my issue...

Jason is right, not just because my younger sons name is Jason also.

I'm no Don ether, it's also how you run the engine, some people come off plane after running the engine hard and just shut off the engine.

A carbed engine needs to be idled 2-3 minutes before being shut down. And with starting follow Jasons advise and let it idle 1-2 minutes when warm.

Good luck

 

[Bondo]

Re: Don I've been thinking about my issue...

once I get it started the engine has a hard time staying running. Rough idling. I have to get it started and almost immediately throttle up so it doesn't die.

Ayuh,....

It sounds like you need a Carb Rebuild,....
The Idle Circuit is Plugged, or Restricted....

It idles Cold, because the Choke is masking the problem....

 

[JustJason]

Re: Don I've been thinking about my issue...

go out and take a run. get it good and hot then shut it down. as quickly as ya can pull the cover and pull the flame arrestor off. look down the carb and see if you have fuel pooling up.

another question i got for ya is your cranking rpms. does it crank (turn over) real fast like your car? does it crank noticably slower when its hot?

 

[Don S]

Re: Don I've been thinking about my issue...

I said in the other post that after an hour the choke plate "will" be closed, what I meant to say it that it may be closed, and if so, it may be in need of adjustment. Since it's open, that's obviously not the problem.
My poor choice of words.

 

[macr6]

Re: Don I've been thinking about my issue...

Jason is right, not just because my younger sons name is Jason also.

I'm no Don ether, it's also how you run the engine, some people come off plane after running the engine hard and just shut off the engine.

A carbed engine needs to be idled 2-3 minutes before being shut down. And with starting follow Jasons advise and let it idle 1-2 minutes when warm.

Good luck

I don't shut it down like you said. I was having run-on issues before this and so I would come off plane and let the engine settle down before killing it.

Ayuh,....

It sounds like you need a Carb Rebuild,....
The Idle Circuit is Plugged, or Restricted....

It idles Cold, because the Choke is masking the problem....

I rebuilt the carb at the end of the year last year. I guess I am going to have to get it professionally done.

go out and take a run. get it good and hot then shut it down. as quickly as ya can pull the cover and pull the flame arrestor off. look down the carb and see if you have fuel pooling up.

another question i got for ya is your cranking rpms. does it crank (turn over) real fast like your car? does it crank noticably slower when its hot?

captJason, If I do have fuel pooling up then what? If I don't then what?

Also, it turns over the same as when it's cold. No real noticeable difference.

I said in the other post that after an hour the choke plate "will" be closed, what I meant to say it that it may be closed, and if so, it may be in need of adjustment. Since it's open, that's obviously not the problem.
My poor choice of words.

So I am back to square one?

Thanks for taking the time guys.