Surging idle

B

BRIELLY

Junior Member
I just put the boat in the water today. It was idling fine in the driveway and was idling good at the ramp but then it just died. When I restarted it it kept on surging up and down. It would smooth out for a few seconds and then start surging again. I took it home and went through the carbs but they were perfectly clean. I'm thinking maybe this is an electrical issue? Its a 91 merc v135. Anyone have any pointers or trouble shooting techniques to get me started? Thanks
 
check the fuel pump. unbolt it from the block but leave all the hoses connected. Squeeze the primer ball. If any fuel comes out from the back you have a bad diaphragm. The leaking fuel goes directly into the crankcase causing erratic idle. It would also run kind of rich. If thats not it I believe that motor has an idle stabilizer module on it. It manipulates the timing to achieve proper idle. Use a timing light to see if the timing is all over the place. If you disconnect it and it idles steady then it is probably bad.
 
Check your fuel filters for water. Its an easy first step before beating your head against a rock tryin to find out whats wrong. Mr.Ethanol is just killing us here in the south so I imagine its gotta be the for yall.
 
This afternoon I ran it off a seperate tank of gas and its still surging. I also tried unplugging the idle stabilizer and checked the fuel pump. Still no good. There seems to be a very large amount of oily gas leaking from the carbs when I tilt it up. I realize there should be some leaking from the carbs but when it forms a puddle in the splashwell it seems too much. This was happening before the idle problem appeared but could it be related and what would cause this to happen?
 
are you sure that you set the float heights correctly on your carbs? Have you checked the fuel pump yet? It really sounds like that could be it.
 
The floats were perfect. I took the fuel pump off and squeezed the bulb and got no gas out of the back. I even took it apart and checked but everything was good.
 
maybe you have a coil or spark plug dropping out. you can pull 1 spark plug wire at a time to see if the surging goes away. Is it only at idle that you have this problem?
 
I didn't take the boat out but it seems to smooth out when I rev it up. When i used the spark checker I didn't notice the spark stopping on any of the cylinders. I'll try pulling off the wires to see what happens today.
 
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I changed the plugs and checked compression today. Its an even 105-110 on all cylinders. Its weird becuase it will idle perfect for a minute and then all of a sudden surge up in rpm's and blow out quite a bit of smoke.
 
have you had any luck? I've been towing non stop all weekend. Maybe I could take a look at it for you. It would only cost you a couple cold ones:beer:
 
Cold ones are in the fridge waitin for ya. At this point I can't tell if its a problem with the linkage or possibly something ignition related. I had it running steady at 600 rmps but when I try to adjust the idle it barely responds. Then it will all of a sudden shoot up to 1500 rpms and stay there until I fool with the idle adjustment. I did have the throttle and shift cables off when I redid the transom so possibly something is out of adjustment. If you can help me out that would be great just pm me your contact info. I do have it scheduled to go to Fullers for repair on Saturday so I'm not sure if that gives you enough time to take a look.
 
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