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Author Topic:   Mercury 90hp 4 Stroke Idle
Moby posted 07-07-2003 05:03 PM ET (US)   Profile for Moby   Send Email to Moby  
My new 2002 Mercury 90 4S came from the dealer with the idle set at 1000-1100 RPM. Naturally, when I shift into and out of gear, there is a noticable "clunk". The salesman told me that "That's how the 4-Strokes idle and shift."
My BS detector is going crazy!
What should the idle be? It seems like 700 to 800 RPM would be better.
Jarhead posted 07-07-2003 06:27 PM ET (US)     Profile for Jarhead  Send Email to Jarhead     
The "clunk" is normal. It is the nature of the beast. [4 stroke]

As for the idle... My '03 115 Merc 4s idles right at 800 RPM and seems to me to be a little slow. Maybe somewhere in between your 1,000 and my 800 RPM might be the answer?

dgp posted 07-07-2003 09:47 PM ET (US)     Profile for dgp  Send Email to dgp     
Idle speed on the engine should be set in-gear. Check your owners manual but I think it's 750 RPM
Jarhead posted 07-07-2003 10:00 PM ET (US)     Profile for Jarhead  Send Email to Jarhead     
Check my owners manual for '03 115 4s Merc.

Idle speed in neutral gear.

Fully warmed up. 750 plus or minus 50 RPM.

I would think the 90 would be the same?

dogfish2 posted 07-09-2003 12:04 AM ET (US)     Profile for dogfish2  Send Email to dogfish2     
The recommended idle speed, in nuetral, for the Merc 90 4s is 850 rpms, + or - 25 rpms, as it is a carburated engine. The higher rpms also causes it shift a little noisier. The "clunk" is a Merc idiosyncrasy which we live with. The 115 4s Merc is EFI and idles at 750 rpms. Hope this info helps.
Moby posted 07-09-2003 01:42 PM ET (US)     Profile for Moby  Send Email to Moby     
Thanks for the replys. When I have my 20hr service done (approx. 2 weeks), I'll have the dealer lower the idle.
Salmon Tub posted 07-09-2003 03:56 PM ET (US)     Profile for Salmon Tub  Send Email to Salmon Tub     
Shifting into gear at too high an RPM is not good for any gearcase. If you have a manual choke control (mine chokes when I push the key in) then you can do a little trick. When you are ready to shift, choke the engine just for a split second, this will cause the engine to drop RPM's momentarily. Once they have dipped, you can shift at that moment. The rpm's will return to normal a second or so later.
dogfish2 posted 07-09-2003 11:11 PM ET (US)     Profile for dogfish2  Send Email to dogfish2     
That's correct! You should not shift when the idle is too fast. The 4s MERCs, have a "shift interrupt" switch that momentarily cuts-out two cylinders. This slows down the rpms and makes for a smoother shift. Have your dealer check to see if it is working.
Moby posted 07-10-2003 12:38 PM ET (US)     Profile for Moby  Send Email to Moby     
Thanks for the replys.

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