78 Mercury 115 racing out of control at idle

[bigal84]

I am experiencing some problems with my 78 mercury 115. For some reason it is running at wot when it should be idleing. I check the carb butterflies and they are closed and timing retarted all the way i believe. I disconnected the linkage so i could retard the timinig as much as possible, but has no affect on the idle speed. I dont understand how it could be revving out of control with no way to stop it when carbs are closed and timing is retarted. Im not sure where to start with this one. water pump? air leak? I dont know, Pleaase help!

 

[Chris1956]

Re: 78 Mercury 115 racing out of control at idle

It has got to be a timing problem. Remove all the spark plugs. Install all plugs into their wires, and ground plugs 2-6 to the block. Set the motor to top dead center by using a screwdriver thru #1 plug hole to make sure piston is all the way up. Timing pointer should read close to TDC on flywheel decal. Now remove cover on distributor pulley and see if cast arrow pointe to punch mark on flywheel. If not, that is the issue.

 

[bigal84]

Re: 78 Mercury 115 racing out of control at idle

Can it jump timing like that? It has been running great so far this season and then the last time out the throttle on the remote box got stuck at wot. When I got back to the dock ( thank good) I disconnected the linkage on the motor side to retard the distributor and put the remote back into neutrul. Like I said butterflies are closed, but when I start it revs out of control immediatly and sometimes slams into gear hard. Maybee this will help with your diagnosis.

 

[Chris1956]

Re: 78 Mercury 115 racing out of control at idle

Throttle is supposed to actively push throttle closed, with some preload. Throttle therefore should be hard up against idle stop screw on distributor. if this is correct, the next step is to put a timing light on it, and see that idle pickup timing is no more that 6* BTDC.