Motor run on

lmaylen

Have a 2003 180 br with a 3.0 merc cruiser. I am having trouble with run on But it doesn't always idle the same sometimes 900rpm sometimes 650 rpm at idle. Will die ok at 650. I don't see any linkage problem. Anybody have a idea what might be problem

aero3113

Maybe you have the wrong spark plugs installed? If the plugs are running too hot this can cause your issue.

212rowboat

concur on the plugs.. 

if your linkage all the way to the butterfly is proper, as you say, i would be looking for a vacuum leak... vac leaks also cause dieseling, and would also explain your high idle at times.. they can be a bear to track down.. i often use a can of ether, carefully sprayed around intake manifold on a running engine.. when rpms pick up, youve fed your engine with the ether via the leak.. it takes a lot of time off tracking it down otherwise.. 

212rowboat

oh... bad gas will cause dieseling, but not likely the high idle. 

lmaylen

thanks for the info. Gas good used high octane. Going to look for vac leak

212rowboat

that is sometimes exactly what it is, though... :-)

a really hot engine will ignite on and due to compression, which is what a diesel does... it won't do it but for a second or two, though.. to truly 'run-on', it needs air and a hot spot in a cylinder to ignite..

lmaylen

Since I am new to this sight I didn't know how to get back to here any way I left my problem fix on new discussion. Main problem not going back to full idle stop fixed that problem adjusted idle mixture opened 1/4 turn and put back in factory recommended plugs seemed to have resolved problem. I now have good idle and dies. Like it should. If you guys didn't see other post. Thanks fou your input. Larry

Michael T

With some of the older 3 liter engines (particularly OMCs) there is a mechanical shift detente that slows the engine idle to almost stall prior to shifting. It is really a small roller that runs over a cam like shift lobe. These can get out of adjustment too and cause all kind of surge and idle nonsense, although I think you have solved the cause of your trouble. If not take a look at the shifter plate on your engine. Regards MT