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Merc 150 gear ratio

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tophawg

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"What gear ratio gearcase shou

"What gear ratio gearcase should a mid 80's merc 150 use in low elevation,standard rotation? I have been helping a friend with this motor after it was put together with a gearcase off a 175 and his bassboat wont pull itself out of the water onto plane and I am thinking the gear ratio and prop are wrong."
 
I will agree this motor has be

I will agree this motor has been a real problem for him and I have offered to help just trying to start with basic stuff before we get into it real deep.After looking around a bit it looks to me there is only a small difference in ratios.Is this correct?If so then its probably not the issue.The carbs do open all the way to full throttle but it just will not pull out of the water.
 
"Agree with Jeff. Even with th

"Agree with Jeff. Even with the wrong gears it wouldn't make a significant enough difference such as you describe.

Depending on the exact model, the 150 would have had either 2.00:1 (2 liter block) or 1.87:1 (2.5 liter block) - a few models with the 4 1/4" gearcase (some XR6's) used a 1.78:1 ratio.

The 175 would also run 1.87:1 gears.

In any event, regardless of the gears, a simple prop change would even things out - if required to get the max rpms up where they should be at wide open throttle.

The first thing I would check is the compression. If she can't even get the boat up out of the water I would expect to see a couple of low cylinders..."
 
An automotive timing light - p

An automotive timing light - portable type that is powered by a 12 volt battery.

With the help of a buddy you can run the boat under "real life" conditions and check for spark at various rpms etc - if necessary...
 
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