Lost top RPM on 1990 200 XP.

Motor Background: The motor is a 200 HP “XP” Evinrude motor, Model No. E200STLESE, S/N G02519201, received new on 10/21/89. It is on a Bass Cat Pantera II bass boat. I use only 93 octane Shell gas and OMC oil. I switched to Evinrude Ram oil on 7/11/02 and switched to XD-100 on 6/8/05. Since 3/15/99, I have added Evinrude 2+ 4 fuel conditioner and Evinrude Carbon Guard to every gallon of gas put in the tank. The motor is used only in fresh water. The motor gets very little use which I know is a problem. I installed an hour meter on 6/10/99 and it has 40 hours to date. New thermostats have 30 hours and new water pump has 13 hours of use.<br /><br />Problem: The last time I ran the motor and tried WOT it peaked at 5500 RPM (It has run 6000 RPM in the past), and slowed to 5000 RPM. I went to idle, tried to plane twice with out success. I idled for maybe 5 minutes, then it would plane and run OK the rest of the day but I kept it below 4000 RPM. I was afraid to try WOT again. I got no alarms, and it starts and idles OK. The motor was decarbed once by a dealer on 9/6/96. The carbs have never been rebuilt. <br /><br />Checked so far:<br />1. Compression: All cylinders at 75 to 80 PSIG with motor warm (But I forgot to open throttles) (Is this pressure too low?)<br />2. Water flow good on both sides (Ran briefly on hose with thermostats/ covers removed. The passages looked clean) Also, checked thermostats (pan of hot water with thermometer, test blowing).<br />3. The water pressure gauge has never worked on this motor. After two tries with the dealer in 1989, I gave up. It is teed into the line coming from the starboard side of the adapter to the water control valve. Is this the correct connection point? During this recent test, (and after bleeding air from the line) at idle the gauge would show no pressure but would show 5 to 6 PSIG when I created backpressure by putting my finger over the pee hole.<br />4. Looked in cylinders with probe light and my 67 year old eyes didn’t see anything unusual – but could not see all of piston/cylinder. There was some (my untrained eye thinks minor) carbon on top of pistons. <br /><br />What next and in what order?<br />1. Try WOT again? (The problem may have cleared)<br />2. Do a decarb?<br />3. Pull heads?<br />4. Rebuild Carbs?<br />5. Other?<br /><br />I have the OMC Service Manual and Parts catalog. However, my only experience with outboards is changing plugs, changing lower unit oil, and changing water pumps. How difficult is it to rebuild carbs on this motor? I have pressured air. <br /><br />Thanks for your advice.

Re: Lost top RPM on 1990 200 XP.

Sounds more like your losing spark to one cylindeer Tex. It can happen and the only way you'll know is by rpm. Run a spark test and make sure you got spark to each cylinder. spark should jump at least a 1/2" gap with a strong thick spark.<br /><br />Compression seems a little low but with in the 10% range. I's run a decarb and test again. Can you get another compression gauge to cross check yours?

Re: Lost top RPM on 1990 200 XP.

Thanks for your ideas OBJ. It will be a week or so before I can get back on the motor.<br />TH