1988 MERC 50 LOSES HIGH END RPM'S

[BASSTRACKER88]

MY BOAT WILL PLANE OUT (5700RPM'S) THEN AFTER ABOUT 1 OR 2 MINUTES THE RPM'S CUT DOWN TO BETWEEN 3 AND 4000 AFTER A FEW MINUTES. MY TANK VENT WAS OPEN. I PUMPED THE FUEL BULB WHEN MY MOTOR LOST ITS HIGH END RPM'S AND IT DID NOTHING. I DID NOTICE THAT MY VOLTAGE WOULD GET HIGHER AND HIGHER THE LONGER I RAN THE MOTOR AT HIGH RPM'S. I'm talking 15-16 volts high. i ordered a rectifier, new impeller, and a thermostat to put in. If anybody has any other suggestions, please let me know. I just bought this boat last week and would really love to get it running right. THANK YOU ALL IN ADVANCE

 

[BASSTRACKER88]

Re: 1988 MERC 50 LOSES HIGH END RPM'S

geeze all, not one response, oh and this is a 45 hp, it says classic 50 on the side, but had a 45 on the plate.<br />thanks anyway

 

[riverebel]

Re: 1988 MERC 50 LOSES HIGH END RPM'S

I have a 1995 60 hp that was doing the same thing almost but it would run about 1/2 hour then die down to 3000 rpm.It was getting about 16 or 17 volts also,and the tach would quit working.after it sat for awhile it was good to go again.I replaced the rectifier/regulator & it took care of the problem.Now just gets up to 13.6 volts

 

[Ken G]

Re: 1988 MERC 50 LOSES HIGH END RPM'S

I had the same motor on an '88 Bass Tracker that I bought new in 1988. Four months after I bought it I was on a fishing trip when the motor would only run about half throttle. I took it back to the dealer and they replaced the switch box. Try checking each cylinder for spark when the problem occurs, you probably are loosing spark on 2 cylinders.<br /><br />I doubt if the voltage irregularities are related, and your rectifier is probably fine. Most, if not all, Mercurys output varying voltages depending on rpm's.

 

[BASSTRACKER88]

Re: 1988 MERC 50 LOSES HIGH END RPM'S

First of all thank you for replying. I replaced the rectifier and took the boat out. I ran it for an hour or so. The rectifier fixed the high voltage output, but not the motor problem. I noticed that when the motor would start to die down that I could sometimes hit the choke and it would rev back up. If I waited to long to hit the choke, I could shut the motor down and reach back and pump the fuel bulb 2 or 3 times and then fire the motor up and it would run fine. I took it to the boat mechanic, he is going to clean up the carbs and rebuild them if needed. I hope this fixes the problem, since I just bought the boat and haven't gotten to enjoy it. Oh by the way around what speed should I get on the water? The best I could get was 26 or 27 (5700 rpm). The prop is bone stock. My mechanic says that I should be able to see about 35 out of it. Thank you guys. Oh just wanted to add I caught a 20 inch rainbow trout yesterday !!!! Yippeee!!

 

[MercNdude]

Re: 1988 MERC 50 LOSES HIGH END RPM'S

I'm having a similar problem with my 140. There are a couple of "must do's" before you go into the electronics. Most of the time, the trouble is fuel oriented and simple. Repleace any fuel filters in fuel tank, lines and at fuel pump. Check lines for crimps or bad seal from cracks or clamps at connections. Look for crimps or equipment that may be pinching your fuel feed lines prior to the fuel pump. The fact that you get good results from the choke and bulb tricks, speaks volumes. Stay there for awhile and perhaps save some $$. Good luck! P.S. mine was a chewed fuel line right at the fuel pump with no clamp to keep air out.