25hp piston slap?

I have a 25hp mariner model 25e, probably early 1970's vintage. Compression seems to be ok, don't have the stuff to do a leakdown test. I am preparing to overhaul the carburetor. The fuel pump appears to be ok. The engine does not keep running (need to choke it on and off to keep it going), burps out of the carb every few seconds when at low rpms, and when at high throttle it sounds like piston slap (you know, like a diesel on a cold morning). Gee, reading this makes me wonder why I am bothering to fix it. Anyways, my question is: Could this piston slap sound be due to the wrong fuel mixture and get fixed when I do the carb? Or, does this sound like it isn't worth fixing the carb and I should just part it out? Thanks in advance!

Re: 25hp piston slap?

is this at high throttle under a proper load or in netrual?<br /> usually by the time the pistons slap they wont idle and some have poor compression. while the carb is off take a close look at the reeds.

Re: 25hp piston slap?

"Piston Slap" can be confused with detonation. Neither is good.<br /><br />Detonation can be caused by a lean mixture.<br /><br />You're on the right track to be looking into/rebuilding the carb.<br /><br />You might want to do this too.<br /><br />See below.<br /><br /> http://www.iboats.com/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic;f=36;t=000016

Re: 25hp piston slap?

Thanks guys! I'll have the carb off later today, will check the reeds and start decarbonizing the pistons. Oh, the slap was without load. Now that you mention it a load might eliminate that - so it is worth doing the carb.