Running at 1/2 Throttle Only

8

84kickassrenken

Cadet
Joined
Jun 24, 2010
Messages
8
I have an 85 MCM140 mercruiser. 140 horse 3 liter. The engine only wants to run at 1/2 throttle and above. The engine sputters and stalles when trying to idle. I cleaned all the fuel filters (one above the fuel pump and right before the carb) and checked the gap in the plugs and points. All are set to the manuf. set range. I have the points gapped at 19 degees and the plugs at 35 degrees. I just cant seem to figure this one out. Any points will help me alot...Thanks
 
Don S

Don S

Honorary Moderator Emeritus
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Aug 31, 2004
Messages
62,321
Re: Running at 1/2 Throttle Only

Carb may be all plugged up in the idle circuit, making a rebuild necessary.
 
superbenk

superbenk

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Joined
Oct 27, 2008
Messages
2,022
Re: Running at 1/2 Throttle Only

Timing could be off. Points, cap, rotor, wires could need replacing.
 
Bifflefan

Bifflefan

Commander
Joined
May 27, 2009
Messages
2,933
Re: Running at 1/2 Throttle Only

I agree with DonS.
Time to rebuild the carb.
 
8

84kickassrenken

Cadet
Joined
Jun 24, 2010
Messages
8
Re: Running at 1/2 Throttle Only

Thanks fellas for your help. This will be my first rebuild. Are there any set of instructions available to follow? Basic guidlines? I will purchase if needed.

CARB INFO:

2 barrel Mercarb
#1389-9562
Rebuild kit 804844
 
JustJason

JustJason

Vice Admiral
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Aug 27, 2007
Messages
5,319
Re: Running at 1/2 Throttle Only

Before you jump to the carb, start with the basics....

1. whats are your compress numbers?
2. what is your dwell angle, base ignition timing, and it's advance timing?
3. have you read about a boat side fuel system test yet, it's found in the adults only section.

Troubleshoot in this order
1. Mechanicals.
2. Ignition
3. Fuel

If you skip or jump around, you'll only be throwing money around. Take your time, and do it right the first time.

Welcome to iboats!
 
8

84kickassrenken

Cadet
Joined
Jun 24, 2010
Messages
8
Re: Running at 1/2 Throttle Only

Thanks for the reply Jason,
Just need some help understanding your post.
I dont know what the "advance timing" would be..or how to check it..
 
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