starts fine ,idles fine, bogs out full throttle.

duckgun

Recruit
Joined
Oct 13, 2004
Messages
2
25 hp mariner 1990 new gas new correct plugs starts ok.but when i open up it cuts off as if gas was disconected it will get me home in fwd just off idle at snail pace if i throttle up does'nt make it to plane a second or two and it fall s off rpms then i twist throttle to neutral to save from stalling it does'nt sputter just cuts out .fuel line bulb has gas pumped up no leaks from tank or engine connections it ran like this last year only time used with different gas &plugs happens right away, hot or cold ,water pump ok .two years ago firt time it happened ran all afternoon on idle speed took home changed to new plugs ran fine till took out yesterday with new stuff must have been coincidence that plugg change caused temporary fix because it didn't work this time sometimes motor is used couple hours a year .
 

JB

Honorary Moderator Emeritus
Joined
Mar 25, 2001
Messages
45,907
Re: starts fine ,idles fine, bogs out full throttle.

Classic symptoms of an engine either running down a cylinder or starved for fuel, Duckgun.<br /><br />Check for a good, hot spark on both cylinders.<br /><br />Also check what she does if you squirt fuel mix (NEVER starting fluid) into the carb.<br /><br />That will tell you if your problem is fuel related or ignition related.<br /><br />Let us know, and good luck. :)
 

MercNdude

Cadet
Joined
Mar 19, 2004
Messages
17
Re: starts fine ,idles fine, bogs out full throttle.

I had the same problem w/ my 140HP inline 6 cyl. Turned out to be a leak in the water jacket gasket on the cylinders. What happens is that as you increase RPM, the cylinders begin to really crank up the vacuum pressure. If there is a small leak (which can gradually or instantly become larger), as the pressure increases it begins to suck water thru the gasket leak and into the cylinders. Once this occurs, you'll get a cut-out of the plugs and the engine just dies, leaving you with a spinning prop at speed. In my case, it would start again after about 5 mins or so of occasionally re-trying. The tell-tale signs are the cut-out at higher RPM and checking for water on the plugs when running in the yard with the water muffs. I pulled my exhaust cover and water jacket cover and replaced the gaskets and it is working wonderfully now. Be carefule not to twist of bolt heads, but if you do, they can be drilled out and helicoil put in to replace the bolt threads. Good luck!!
 

PaulKim

Petty Officer 3rd Class
Joined
Aug 9, 2004
Messages
82
Re: starts fine ,idles fine, bogs out full throttle.

MercDude, that is the same symptoms my Merc 75 was having. Did you get aluminum throwoff?
 
Top