I'm having a similar problem to whitesnooky's 25hp merc. The engine starts fine, idles decent sometimes but was sputtering quite a bit last time I tried it and it runs good up to about 1/2 throttle and then bogs down. It doesn't completely stall just goes to idle speed and then I am able to throttle back up to 1/2. I had this problem a few months ago after I bought it used so I had the carb cleaned and it was running fine till now. I took it to the shop again and they said the carb was clean and that they wanted to test run it to see if they could figure it out but I picked it up before they could because they were taking forever. So after reading the repair manual and looking around online, I'm thinking there might be problem with the float in the carb. When it bogs down, it seems like the engine is flooding instead of being starved of fuel. I think the fuel pump can be ruled out because when I pump the primer bulb when running, the engine seems like it bogs down (floods) even quicker. Could the timing be an issue? Any ideas?
Check your sparkplugs for gunk. Clean and gap to spec, or replace. Check spark is hot. While plugs are out of the block, test the fuel pump. To check fuel pump, disconnect fuel line from carb. Squeeze hose bulb until fuel empties from end of carb hose into a jar. Place thumb over end of hose. Crank engine a few times. Release pressure on end of hose into glass jar. A stream of gas under pressure from the hose indicates a functioning pump. No fuel under pressure indicates faulty pump. Get new pump. Adjusting timing can't hurt and is easy to do. Test run. Still a problem, new carb kit. Clean carb and rebuild. Choking out is a good indicator of a problem with the float and needle valve.
Thanks everyone for the tips. I got a chance to inspect the engine yesterday and noticed both spark plugs were very loose [smiley=dunce.gif]. That could possibly explain the sputtering, flooding of the cylinders and subsequent loss of power. I'll take it for a test run on Saturday and if the problem persists, I'll start the recommended diagnostics. [smiley=1-beer.gif]
