Merc 1500 stalls during acceleration under load

[kip3816]

I purchased a 1976 mercury 1500 that idles fine but stalls when accelerating under load. If I keep slowly working it I can sometimes get the boat on plane and then it runs fine at top end (at least it seems to). I do not know the history of the motor but compression is fine and it appears to be delivering fuel properly. I have checked the ignition timing at idle and it was correct. I am not sure of the secondary throttle pickup adjustment or the condition of the inside of the carbs. Would you reccomend that a carb rebuild be tried first? I operate the boat at altitudes of 4000 to 5000 feet. <br />Any help will be appreciated.

 

[Bear]

Re: Merc 1500 stalls during acceleration under load

The carbs need more air I think. I also think the carbs are jetted for use at sealevel. Maybe 5000 feet (1500 meters?)isn't that high. Let's see if there is any other suggestions here soon.<br />/Bear

 

[ODDD1]

Re: Merc 1500 stalls during acceleration under load

KIP, before you go at repairs, how are you propped? if you are not hitting max rpm's this could be all your prob...these motors are sensitive to being over propped...when everything is right on these motors and you put too much prop on em, they bog......otherwise, these motors generally bog because they are to lean...if the thing is jetted for sealevel and you are up 4000, is probably not your prob....

 

[kip3816]

Re: Merc 1500 stalls during acceleration under load

I am only running a 15 prop and am not having a problem reaching max RPM. I am concerned that there is either a problem with the syncronization of the throttle and ignition timing or that the main jets in the carbs are either clogged or the wrong ones. I can sometimes trim the engine up high enough to let the prop cavitate a little and get over this "problem area" in the throttle and then trim it back down and it will run at full throttle but seems pretty weak after a few minutes. I pulled the plugs and they are not really fouled but have some sticky brown liquid spots on them. It seems like the engine is getting a little hot as well (but I have not ran it very long to see if it really overheats). I can also sometimes simply quickly give it full throttle and avoid the mid range area and it pulls up on plane very quickly. It also starts to have problems idling after about 15 minutes of trying to run it fast, this seems to be corrected after it cools off. Thanks for any help.