Mercury 100hp sounds really rough @ low rev

khc1970

Petty Officer 2nd Class
Joined
Sep 19, 2004
Messages
109
Hi, I live in the UK and have just bought a 2nd hand mercury 100, serial no:9530539, using one of the site suggested here, it's traced to being a 1989 model.<br />On idle, the engine sounded really rough, like a badly out of tune 2-stroke engine, except it was serviced last month after I'd bought it. It's ok when rev tho. <br />This led me to believe it is a 2+2 as suggested in some of the threads here. Except the mechanic (mercury authorised agent) said he had never heard of a 2+2. Is there anyway I can find out for sure if it is indeed a 2+2 or otherwise? Were all the 1989 Mercury 100hp are 2+2?<br />Also, on her maiden voyage, it used about 30 litres of petrol to cover anout 30 miles, mostly at 3/4 to full throttle, is it normal usage for this type of outboard?<br /><br />Thanks in advance.
 

Laddies

Banned
Joined
Sep 10, 2004
Messages
12,218
Re: Mercury 100hp sounds really rough @ low rev

all 4 cyl. 100s are 2/2 find a new mechanic
 

BikerBoater

Cadet
Joined
Sep 4, 2004
Messages
13
Re: Mercury 100hp sounds really rough @ low rev

Hello,<br />I have a 1988 100 HP 2+2 (Sea Ray Edition). As far as fuel useage, I believe it uses 4 liters for each 10 HP every hour at 3/4+ throttle. So for an hour with a 100 HP you would use 40 liters. Maybe a little less because I'm converting from US gallons. This amount could vary due to load on the engine (weight of boat & gear). Also, all Mercury 100 HP / 4 cylinder models are 2+2. Your mechanic should know this, my mechanic does and so does most of the readers here. These engines do sound a little rough from idle to around 1800 RPM and then the bottom 2 cylinders fire up. You use the words "really rough" I wouldn't describe mine in such a strong manner. You may need a simple fuel pump rebuild or replace the spark plugs. I would need more information to be sure. Although, I usually replace the plugs and rebuild the fuel pump annually. I really like this engine and believe after a while you will too.
 

khc1970

Petty Officer 2nd Class
Joined
Sep 19, 2004
Messages
109
Re: Mercury 100hp sounds really rough @ low rev

Thanks for the replies, it helps to ease my concerns.<br /><br />It sounds really rough on start up, abit like my old lawnmower, but once it warms up, it settle down a bit although it still sounds 'rougher' than when it reaches 2000 rpm.
 

Clams Canino

Commander
Joined
Jan 10, 2004
Messages
2,179
Re: Mercury 100hp sounds really rough @ low rev

Ya - it's a 2+2. I'm sorry.<br /><br />-W
 
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