1990 Johnson 70HP poor idle

[BobEhlers]

I recently purchased motor with only 50 hours. Motor idled poorly so I changed fouled plugs, fuel filter and fuel lines. It started right up and ran like a champ in the tank. After several times restarting her up I have noticed the idle starting to jump & down on the RPM gauge. Can anyone please enlighten me why this would happen? Is it bad to let these motors idle at low RPM's ? Your comments are much appreciated !

 

[MERCMAN]

Re: 1990 Johnson 70HP poor idle

FIRST THING YOU NEED YOU DO NEED TO DO IS CHECK COMPRESSION SPECIALLY CYL#2 IF OK PULL AIR BOX AND PULL BOWL DRAINS AND LOOK FOR TARNISH IF SO NEED TO CLEAN CARBS

 

[BobEhlers]

Re: 1990 Johnson 70HP poor idle

Mercman:<br />Thank you very much for your advise. I was a little surprised after reading my manual about cleaning the carbs. Is this a job that can be done by a careful amateur or is it something that you would recommend be done at the OMC shop? It appears that the carbs have to be completly disassembled ?<br />Thanks again..Bob

 

[MERCMAN]

Re: 1990 Johnson 70HP poor idle

YOU SHOULD'NT HAVE ANY PROBLEM WITH THIS JOB JUST BE SURE SET FLOAT LEVELS LEVEL. WHEN YOU REMOVE ADJUSTMENT NEEDLES REMOVE THE BRASS HOLDERS WITHOUT DISTURBING THE NEEDLES ALSO MAKE SURE THOTTLE PLATES ARE CLOSED WHEN YOU INSTALL THE LINK ARM PART# FOR CARB KITS 436701 OEM TAKE YOUR TIME AND GOOD LUCK PS AGAIN CHECK COMPRESSION AND IF POSSIBLE LOOK INSDE FOR SCUFFING EXSPECIALLY ON CYL#2 ON THE EXHAUST SIDE THESE MOTORS ARE BAD ABOUT RUNNING HOT ON THIS CYLINDER EXSPECIALLY ON PONTOON BOAT OR A ALUMINUM BOAT WITH RIVITS CAUSEING CAVITATION IN COOLING SYSTEM