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140 merc I/O no power out of hole


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07-08-02, 08:17 AM   #1  
stevei44
140 merc I/O no power out of hole

I have a mid-70's 140hp mercruiser on a 16.5' Mark Twain tri-hull
It takes almost 1500 yards to plane out and run above 5 mph. It runs at 2000 rpm and pulls like I have a car hooked to the back of it. Once it planes out it runs 27 mph at 4000 RPM like it should. I have rebuilt carb, and ignition. It has a 17.5" prop which is right and no water in the bilge. Any help would be greatly appreciated

 
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07-08-02, 05:03 PM   #2  
JAllen72
A couple of things come to mind. Is your prop in good condition and do you have power trim. If so is it working? This sounds like an awful long time to get going. I have the same motor on a 16.5 Cris Craft v hull and it gets out of the hole real well unless I am carrying to many passengers or all my passengers are in the rear. then it is very slow to get going. Is your timing correct would be my next question. Good luck!

 
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07-12-02, 11:28 AM   #3  
stevei44
I got fed up with it finally and tore into it after checking compression and found none in 2 and 3. I found a blown head gasket between 2 and 3 and a chipped ex. valve in 3. What could have caused this problem???

 
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07-20-02, 06:38 AM   #4  
The four cyl engines are blowing head gaskets
from timing. You should run the advance at 6 btdc
on that year. Have the machine shop put in hardened
exhaust seats to bring you up to spec with todays fuels.
Scott

 
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07-22-02, 11:37 AM   #5  
stevei44
The timing mark is at about 11:00 and 6 BTDC is at about 2:00 but it runs fine there, why is that? I tried moving it but it falls off and dies. #1 cylinder is up at 11:00 as well.

 
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07-22-02, 06:40 PM   #6  
This may be a case where yopu just need to get a manual.
I think we are losing some info in the translation.
All engines are timed using the #1 cylinders spark
as read through the wire with an inductive pickup
timing light, right?
And you are refrencing that spark against the
timing pointer on the front cover of the engine
as the "0 tdc" mark passes across it, correct?
Good!

 
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