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I have tried everything to cure a rough idle on a 1988 Merc outboard, Black Max 200. I just boat the boat and it runs great above 2,200 rpm. Otherwise it is rough and stumbles. Here is what was already completed.
1) Power tune 2X
2) New plugs (used NGK BU8H, OEM plug)
3) Fuel filter
4) New stator, trigger, advance module.
5) Rebuilt carbs
6) Emptied fuel tank
7) Emptied oil tank (refilled them of course)
8) Compression checked
I also can't find out what the correct jets are. I have the shop manual, but the carb numbers in the manual don't match up to the installed carbs. I think the carbs are OEM based upon the previous owner. Numbers on the carb include 1374-5427A (on all three) and then top carb 46 11488, middle carb 46 21488, top carb, 46 31528. Also, all carbs have "WH" on the flange. The manual has a chart that shows the jets (main, idle, and vent) for each carb, but the carb no. is shown in the book as WH1, WH2, WH3...WH29. Most of the jets match the carb in the manual for WH28, but the main jets are larger consistently across the board.
Can anyone provide me some advice.
Thanks a million,
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Hey,
Do those carbs have idle screws and limiter caps (WMH's) or are they the old style WH's. either way, there are several things that can cause it. #1, have you checked to see if all 6 holes are running at idle by removing the plugs leads one at a time using a pair of grounded pliers? Each one, when removed, should drop idle rpm the same amount. If you can remove one or more wires with no change in rpm, then that one or more isn't running, either due to no spark, no fuel, or too much fuel. Try that and let me know. MAKE SURE YOU USE A PAIR OF INSULATED PLIERS WITH A HEAVY GAUGE GROUND WIRE FROM THE PLIERS TO THE BLOCK, OTHERWISE ITS GONNA HURT LIKE HELL, AND MAY DAMAGE THE ELECTRONICS!!
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Try WWW.ScreamandFly.com (http://WWW.ScreamandFly.com) in the tech forums. US1 is real good at that kind of problem. He's a formula 1 racer with a lot of carb motor experience.
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I HAD THE SAME PROBLEM WITH MY 2.4. IT WAS A BROKE REED VALVE. AT LOW RPM IT WOULD FLOOD THE HOLE, BUT AT HIGER RPM IT WAS FINE. ON MINE IT WAS EAZY TO SEE OPEN THE BUTTERFLYS AND TAKE A LOOK.
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I does sound like it might be reeds. That's easy enough to check. Use either a small flashlight, or even better a Bend-a-light, open the throttle, and look though to the reed cages. If you need reeds, I handle Boyesons, and you won't find em for less anywhere. :cool:
