1993 70hp johnson runs great but idles like crap

[stelladallas]

Here we go again.....after setting all winter.....we took the boat out yesterday for the first fishing trip. Let me back up just a little, we've seemed to always, ever since we bought this rig, had trouble with it idling. We rebuilt the carbs, put new plugs in, did everything that had been suggested on iboats forums. Nothing seemed to help the idling. Last year, just before our last fishing trip, we were fed up with trying to keep the motor running while trying to drive it onto the trailer, so we dropped it off at Dawson Marine, a well respected boat dealer who is located on our way home. He supposedly did a link and sync to balance the carbs and installed new Champion plugs and on our last fishing trip, of last year, it did seem to idle better. This year, on our first time out, the darn thing seems to miss while sitting at idle all over again, couldn't ask for a better running motor at top end, but just idles very rough. What am I missing here?

 

[emdsapmgr]

Re: 1993 70hp johnson runs great but idles like crap

Was the engine properly winterized, or laid up, for the winter? If any leftover fuel dried up inside the small idle passages, it can restrict fuel flow and can affect idling.

 

[stelladallas]

Re: 1993 70hp johnson runs great but idles like crap

Thank you sir. Do you suppose a can of seafoam would help?

 

[ezmobee]

Re: 1993 70hp johnson runs great but idles like crap

Thank you sir. Do you suppose a can of seafoam would help?

TECHNICALLY SeaFoam is not to clean a dirty carb, it's to help keep a clean carb clean. However, it can't really hurt to try. I had an intermittent hiccup at speed last year that doing a SeaFoam treatment completely solved.

This is what I did. I bought a regular can of SeaFoam and a can of the aerosol version (deep creep I think?) I mixed the can of regular with a gallon or two of pre-mix fuel in a portable tank. I went out on the lake. Removed the motor cover and the silencer on the front of the carbs. With the motor running, I continuously sprayed the deep creep into each carb, backing off when it would start to die. Finally I sprayed a bunch in there till it did die. Let it sit about 15 minutes. Then with the motor connected to my portable tank of seafoam gas, I ran around the lake till it was gone. Problem solved. I ran around like a bat out of hell as that's where my issue was. Yours is idling so you may want to spend more time idling around.

 

[emdsapmgr]

Re: 1993 70hp johnson runs great but idles like crap

As ezmobee says, normally, you can't really dissolve dried fuel gel that's inside the carb from outside of the carb. However, the seafoam is a product that is supposed to clean carbon from the rings/pistons as the fuel passes thru the engine. I'm not sure if it's added to the fuel tank if it would also dissolve dried fuel in those passages as you run it or not. Probably worth a try. A product that is specifically designed to clean dried fuel gel is Gumout, but you are looking at dissassembly of the carbs in order to apply it, too.