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#1
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Surging idle
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
 35. Anyone have any pointers or trouble shooting techniques to get me started? Thanks
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#2
05-26-2010, 08:19 PM
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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.
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#3
05-27-2010, 04:04 PM
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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.
__________________
Elbow Room '85 V-20 Step-Lift Express "Take A Fish Boating" 
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#4
05-27-2010, 06:16 PM
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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?
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#5
05-28-2010, 07:35 PM
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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.
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#7
05-29-2010, 07:23 AM
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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?
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#8
05-29-2010, 08:52 AM
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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.
Last edited by BRIELLY; 05-29-2010 at 09:05 AM.
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#9
05-29-2010, 01:10 PM
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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.
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#10
06-01-2010, 08:23 PM
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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
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