1999 200hp carbed merc no power under load

[On The Edge]

OK here it is. Did a decarb on my carbed merc before winterizing and used Merc power tune ad directed on the can. Let it sit a few hours and took it up the lake for a run. She started (Smoked like a pig but soon cleared) went for a run and it shutters and vibrates wicked bad under load and will not rev up under load. Normal WOT speed is 42mph trimmed and light. I can not get her over 27 mph trimmed and light. Changed out the plugs thinking the decarb fould a plug or 2. Same problem. Changed filters and took a fuel sample thinking it was unrelated to the decarb and i just got some bad fuel. Fuel is clean. Ran it on a 6 gallon remote tank still the same.

The motor runs ok at idel and starts. It is a little tempermental when starting cold. The throttle is fairly responsive in nutral. It makes no unusual noises when starting or running and does not smoke more then usual.

Did the typical test and here is were i am so far. Fuel delivery and presure is good. As are the carbs (rebuilt in the spring). Did a compression test and had good even #'s. All cylinders in the upper 1 teens across the board 5lbs Between the highest and lowest. Next was electrical. Spark test at each cylinder revieled nice blue spark at 7/16 gap also across the board. So my next thought was to look for a short or jumping spark so i fired her up in the dark. Again all was good with no jumping sparks. Got the lights back on and started looking over the entire motor for signs of a loose or broken wire, or hose or disconected linkage. And there it was staring me right in the face through the space between the top and middle carb. A split in the fuel enrichment valve hose. The hose that goes from the middle carb down to the bottom carb had a 1.5" long split along its length were it connects to the middle carb's barbed fitting. The only thing that was holding it on the barbed fitting was the fact it was 10 years old and was stiff and formed to its location. There was enough length to cut off the split section so i cut it off, re routed it and reconnected it. I will be dropping it in the local lake tomorrow for a test run. I do plan on getting a new hose so it can be routed properly. I do know this find will help with the cold starts but not sure how that system leak would affect the perfomance of the engine durring normal opperation in the upper RPM range under load. Would the split in this hose cause some sort of a Vacume leak in the carb? Tomorrow will tell the tale.

It does run noticeably smoother at idle. If this is not it then i am kinda lost. The basic elements required for an older carbed engine to run are all present and working, Fuel, Spark & Compression.

The Merc Power tune for the Decarb was not introduced into the fuel system it was sprayed directly into the throat of each carb as directed while running the motor. Both Filters are new and fuel lines were replaced in the spring when i rebuilt the carbs..


Any advice or coments are welcome.