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Author Topic:   Any Merc experts out there?

JCL posted 09-20-2002 12:08 PM ET (US)
Mercury 1998, 4 cyl, 100hp, has mode that drops to 2 cylinders under 1800 rpm. Is there any way to improve the low speed performance.? Idle and low speed operation very rough, can't troll, dies. Starts cold fine, runs great. Had a dealer check it out but could not find anything wrong. Nature of the beast?
Had hot restart problem but that has been resolved.
thanks for all the feedback. This is a great website. Am a 20 year Montauk owner.
JCL

hauptjm posted 09-20-2002 02:36 PM ET (US)
Gap your plugs perfectly. I'm told the effects of just a slight incorrect gap on the spark plugs will dramitically effect your low speed operation. Also, use NGKs. A cheap fix. If it doesn't work, at least you have new plugs.
Clark Roberts posted 09-21-2002 07:37 AM ET (US)
JCL, the spark plug advice is good and also check adjustment of the "idle air adjustment needle valve" located atop each of the two carbs that operate at idle (bottom two but I may be wrong...could be top two... you can tell by looking as the idle inactive carbs have no idle air adjustments just a cover over the idle tower). Turn ClockWise (CW) until lightly seated and then back off (CCW) one and one half turns... start engine and let warm-up then turn each in succession first CCW (richer)until engine runs rough them CW until same ...then try to adjust to mid-point. Do this both carbs..note> bias adjustment to richer mixture is best! If this doesn't do it then yank carbs/clean/replace and adjust as described above. Your engine idles on timing only and easy to get a few more rpm at idle if needed. Good luck.. clark.. SCN

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Author	Topic: Any Merc experts out there?
JCL	posted 09-20-2002 12:08 PM ET (US) Mercury 1998, 4 cyl, 100hp, has mode that drops to 2 cylinders under 1800 rpm. Is there any way to improve the low speed performance.? Idle and low speed operation very rough, can't troll, dies. Starts cold fine, runs great. Had a dealer check it out but could not find anything wrong. Nature of the beast? Had hot restart problem but that has been resolved. thanks for all the feedback. This is a great website. Am a 20 year Montauk owner. JCL
hauptjm	posted 09-20-2002 02:36 PM ET (US) Gap your plugs perfectly. I'm told the effects of just a slight incorrect gap on the spark plugs will dramitically effect your low speed operation. Also, use NGKs. A cheap fix. If it doesn't work, at least you have new plugs.
Clark Roberts	posted 09-21-2002 07:37 AM ET (US) JCL, the spark plug advice is good and also check adjustment of the "idle air adjustment needle valve" located atop each of the two carbs that operate at idle (bottom two but I may be wrong...could be top two... you can tell by looking as the idle inactive carbs have no idle air adjustments just a cover over the idle tower). Turn ClockWise (CW) until lightly seated and then back off (CCW) one and one half turns... start engine and let warm-up then turn each in succession first CCW (richer)until engine runs rough them CW until same ...then try to adjust to mid-point. Do this both carbs..note> bias adjustment to richer mixture is best! If this doesn't do it then yank carbs/clean/replace and adjust as described above. Your engine idles on timing only and easy to get a few more rpm at idle if needed. Good luck.. clark.. SCN