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merc 15h.p. bogs out at half throttle

D

danestacie

New member
starts and runs great but when i give more than half throttle enginge bogs out compression 110 both cylinders checked carb didnt see any issue new plugs how do you check for crankcase pressure? thanks
 
Check the engine compression. Clean the carb w/an overnight soak in carb cleaner then blow out all the fuel passages w/comp. air.
 
What year is the motor (or do you have the serial) and is it 2 or 4 stroke.

There are some legacy issues with older 2 strokes, so knowing what motor we are dealing with could add to your list of things to check...
 
galamb said:
What year is the motor (or do you have the serial) and is it 2 or 4 stroke.

There are some legacy issues with older 2 strokes, so knowing what motor we are dealing with could add to your list of things to check...
Click to expand...

mercury said its a 1991 2 stroke long shaft I took carb apart soaked it and put rebuild kit with new float wont hit the water until it stops raining someone also said I may have lost a crank seal by power head told me I should do a crankcase pressure test how do I do that? thank you
 
Yes, looks like a 91 - I own the exact same model.

Bogging when you give it gas is generally NOT indicative of a bad crank seal. I have changed many, they do fail particularly on the 6/8/9.9 and 15 horse models (seems when the hit the 20-25 year mark they finally have had enough) but, when you have a bad seal (and it's normally the upper seal) it seems to run fine at higher rpms and dies when you throttle back. The easiest way to tell that the seal is shot is to wipe your finger up under the edge of the flywheel - if it come back "gloopy" (a mess of thick oil/dirt) that indicates that some of your air/gas/oil is blowing by the seal - the gas evaporates leaving the oil behind (the same as if you had sprayed under the flywheel with WD40 or fogging oil).

The same is true with a bad intake cover gasket - you will get an oily mess in the lower cowl, on the right hand side of the motor (looking at it from the prop end), back near the (head) water jacket cover (actually right behind the shift/throttle linkage - the cover with 3 bolts lined up vertically).

Bogging out when you give her gas is more commonly 1) dirty/clogged carb 2) perforated fuel pump diaphragm 3) leak somewhere on the intake side of things sucking too much air 4) clogged gas line 5) faulty tank vent or anti-siphon valve on the gas tank or 6) a bad powerhead base gasket.

When you rebuilt the carb were you careful to ensure that the little ball/spring in the primer were re-assembled correctly? That is the source of a common issue upon reassembly - the little ball slips and causes the engine to flood out, resulting in pulling it apart again (been there myself many times) - so if you experience flooding, that is probably a new, unrelated problem that can be traced back to the primer.
 
just got back from river today same problem surges and bogs down at wot replaced intake gaskets rebuilt carb and new plugs any more diagnois I can do or any thoughts thanks
 
You need to run a WOT plug check to see if she's running on both cylinders. Run it wide open for at least a minute, then shut it down quickly as possible and pull plugs. Do NOT let it idle.

Jeff
 
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