1986 Mercruiser 170 running issue

[Bellman73]

Hello all! new to the forum and have read most of the issues I can find with the Merc 170 inboard. Mine is a touch different as it isn't a starting issue.

I can start normally and run great until I pull the boat into idle while the kids are getting ready to get on the tube etc. Once I get back to the throttle it stumbles and falls all over itself and wont go at all and stalls out. Now, if I let it sit for about an hour it starts to act normal again, but letting it sit and idle will get us right back into the same situation. Does this sound like a carbuerator issue? maybe its getting too much fuel at idle?

 

[nola mike]

Yeah, sounds like it's flooding though certainly other possibilities. Does it happen if you have it sitting at a fast (~1500 rpm ) idle? If you look down the carb throat while idling, can you see fuel from the venturis?

 

[kenny nunez]

Try running the bilge blower, since a 470 is fresh water cooled it builds more heat under the cover. Also buy a new rotor for the distributor.
Just to be sure you can try having the engine cover open before you start to pull the kids. If you are using ethanol based fuel it could be the fuel boiling in the carburetor.

 

[kd4pbs]

Is this a new-to-you boat?
Does this boat have an aftermarket Pertronix electronic ignition module?
When it cuts off, look in the carb to see if the fuel is boiling out (vapor locking).
I, too am an unfortunate owner of a 170, and it does the exact same thing as you describe. Mine does not vapor lock, which leaves me to believe it's the ignition module overheating, but I haven't had the chance to troubleshoot it as of yet. Seems many people don't know whether or not these Pertronix units require a ballast resistor, and if they do, they don't understand how it must be installed.
It's a shame too, because while the 170 is a red-headed step child, I must admit that in this little 17' boat, it pushes it to 55MPH, GPS verified, with an aluminum prop. Quite amazing for that little 4 cylinder engine!

 

[Phillip_333]

Hello all! new to the forum and have read most of the issues I can find with the Merc 170 inboard. Mine is a touch different as it isn't a starting issue.

I can start normally and run great until I pull the boat into idle while the kids are getting ready to get on the tube etc. Once I get back to the throttle it stumbles and falls all over itself and wont go at all and stalls out. Now, if I let it sit for about an hour it starts to act normal again, but letting it sit and idle will get us right back into the same situation. Does this sound like a carbuerator issue? maybe its getting too much fuel at idle?

Is choke opening all the way?