90 HP Mecury 2 Stroke Idle Problem - Moderated Discussion Areas

  ContinuousWave
  Whaler
  Moderated Discussion Areas
  ContinuousWave: Whaler Performance
  90 HP Mecury 2 Stroke Idle Problem

search | FAQ | profile | register | author help

Author Topic:   90 HP Mecury 2 Stroke Idle Problem

Boboe posted 08-08-2005 06:46 AM ET (US)
I have a 2004 Merc that I broke in this year. The motor always idled rough, however, I thought that was due to the break-in gas. Since then I have run about 60 gallons of gas through the motor and the idle has actually become worse.
I called the dealer and he said he can make an appointment for me end of Aug. Not wanting to wait, I pulled the cover of the motor and saw in big letters "Idle Screw Adjustment" staring me plain in the face.
My question is, can I mess with this screw? If so how? Seems odd that a brand new motor would have a problem like this so quickly. The motor runs great otherwise except it sometimes takes two or three cranks to get her started after she's warmed up. Hoping that's related to the idle problem.
Boboe
Clark Roberts posted 08-08-2005 07:49 AM ET (US)
Boboe, your engine idles on timing only and the screw you mention only adjusts the idle timing to speed up or slow the rpm. To smooth out the idle you need to adjust the "idle air" needle valves (screw driver adjustments atop each of the three carbs). The drill: screw each in (clockwise-CW) until lightly seated and then back out (Counter clockwise - CCW)1 1/2 turns; crank engine and,in sequence starting with top carb, turn needle valve CW until engine runs rough and then turn CCW until same then try to adjust to a midpoint between these two positions. Proceed with the other carbs. Now for the best adjustment put boat in water, tie securely to dock and put in forward gear and repeat the adjustments. The engine idle speed and idle air adjustments are best made with engine warm, under load and with water at proper height in engine mid section. The back pressure from water in the mid section is not present with engine running on a hose or in a bucket and with no load. Adjust idle speed with the screw you mentioned (timing adjustment) to recommended speed...around 700 rpm IN GEAR AND IN THE WATER
Engines with rough idle and/or caughing and sneezing can usually be smoothed out by fussing around with fuel:air ratio adjustments as described above. Go for it! happy Whalin... Clark... Spruce Creek Navy
PS>if you can refer to a maint. manual you will find a better description of the process and maybe pictures also!
Boboe posted 08-08-2005 08:56 AM ET (US)
Thanks Clark.
You make it sound pretty darn easy. I will not be able to do this until next weekend. I'll post the results to the board.
Boboe posted 08-21-2005 09:19 AM ET (US)
Update on the idle problem...
Ended up calling the dealer from which I purchased the boat back in March. I talked to the sales manager and explained that coming in was out of the question. He was kind enough to allow me to discuss my problem with a mechanic who was quick to diagnose the problem and suggest a solution. He told me I probably have spark plugs with the letter "Z" in the number and that I should replace them with the same plug with out the "Z". Something about electronics. He also said to not bother with the idle adjustment screws as he seldom touched those on a new engine. He also said don't expect perfection as 3 cylinder engines are known to have these types of problems (let that be a lesson) due to the non-symmetrical design.
I pulled the plugs and sure enough they had the "Z". They also had some black carbon deposits on the top plug. I replaced the plugs and the engine runs 100% better although not perfect as it still occasionally stalls in idle. I'll have them check that when I take it in the winter for storage.
So I did not attempt the idle adjustment as suggested but appreciate the explanation and maybe attempting it in the future.
Bob
bigjohn1 posted 08-22-2005 09:15 AM ET (US)
Clark - that was an excellent suggestion you mentioned on tying the boat to the dock and placing it in gear for best carb adjustement. So many people forget about that little pearl of wisdom. That's exactly how I used to tune my smaller 2-smokes and people used to look at me like I was crazy at the dock. My engines always purred like a kitten though so the joke was on them:-)

Hop to:

Contact Us | RETURN to ContinuousWave Top Page

Powered by: Ultimate Bulletin Board, Freeware Version 2000
Purchase our Licensed Version- which adds many more features!
© Infopop Corporation (formerly Madrona Park, Inc.), 1998 - 2000.

Author	Topic: 90 HP Mecury 2 Stroke Idle Problem
Boboe	posted 08-08-2005 06:46 AM ET (US) I have a 2004 Merc that I broke in this year. The motor always idled rough, however, I thought that was due to the break-in gas. Since then I have run about 60 gallons of gas through the motor and the idle has actually become worse. I called the dealer and he said he can make an appointment for me end of Aug. Not wanting to wait, I pulled the cover of the motor and saw in big letters "Idle Screw Adjustment" staring me plain in the face. My question is, can I mess with this screw? If so how? Seems odd that a brand new motor would have a problem like this so quickly. The motor runs great otherwise except it sometimes takes two or three cranks to get her started after she's warmed up. Hoping that's related to the idle problem. Boboe
Clark Roberts	posted 08-08-2005 07:49 AM ET (US) Boboe, your engine idles on timing only and the screw you mention only adjusts the idle timing to speed up or slow the rpm. To smooth out the idle you need to adjust the "idle air" needle valves (screw driver adjustments atop each of the three carbs). The drill: screw each in (clockwise-CW) until lightly seated and then back out (Counter clockwise - CCW)1 1/2 turns; crank engine and,in sequence starting with top carb, turn needle valve CW until engine runs rough and then turn CCW until same then try to adjust to a midpoint between these two positions. Proceed with the other carbs. Now for the best adjustment put boat in water, tie securely to dock and put in forward gear and repeat the adjustments. The engine idle speed and idle air adjustments are best made with engine warm, under load and with water at proper height in engine mid section. The back pressure from water in the mid section is not present with engine running on a hose or in a bucket and with no load. Adjust idle speed with the screw you mentioned (timing adjustment) to recommended speed...around 700 rpm IN GEAR AND IN THE WATER Engines with rough idle and/or caughing and sneezing can usually be smoothed out by fussing around with fuel:air ratio adjustments as described above. Go for it! happy Whalin... Clark... Spruce Creek Navy PS>if you can refer to a maint. manual you will find a better description of the process and maybe pictures also!
Boboe	posted 08-08-2005 08:56 AM ET (US) Thanks Clark. You make it sound pretty darn easy. I will not be able to do this until next weekend. I'll post the results to the board.
Boboe	posted 08-21-2005 09:19 AM ET (US) Update on the idle problem... Ended up calling the dealer from which I purchased the boat back in March. I talked to the sales manager and explained that coming in was out of the question. He was kind enough to allow me to discuss my problem with a mechanic who was quick to diagnose the problem and suggest a solution. He told me I probably have spark plugs with the letter "Z" in the number and that I should replace them with the same plug with out the "Z". Something about electronics. He also said to not bother with the idle adjustment screws as he seldom touched those on a new engine. He also said don't expect perfection as 3 cylinder engines are known to have these types of problems (let that be a lesson) due to the non-symmetrical design. I pulled the plugs and sure enough they had the "Z". They also had some black carbon deposits on the top plug. I replaced the plugs and the engine runs 100% better although not perfect as it still occasionally stalls in idle. I'll have them check that when I take it in the winter for storage. So I did not attempt the idle adjustment as suggested but appreciate the explanation and maybe attempting it in the future. Bob
bigjohn1	posted 08-22-2005 09:15 AM ET (US) Clark - that was an excellent suggestion you mentioned on tying the boat to the dock and placing it in gear for best carb adjustement. So many people forget about that little pearl of wisdom. That's exactly how I used to tune my smaller 2-smokes and people used to look at me like I was crazy at the dock. My engines always purred like a kitten though so the joke was on them:-)