115 merc older cant get high rpm in gear

[halifaxboater]

hi im a newer boater .bought a older 115 merc on a 20 foot glastron .i used it all summer always hard to start but worked good no knocking runs smooth.cruises real nice at 25 mph.but last time out got up on plain then rpms dropped from 3200 to 1400 went back to dock started rite up reved rite up in nutral put in gear stalled.finaly got it to go but wouldnt go over 1400 rpm except once it kicked in rite back up to3200 for aboat 20 sec then back to 1400.i have aboat 132 psi on all cylinders except #3 96 psi witch is what it had when i bought it. it does not charch rite but ive been running all summer on full charched battery never had a problem. any idears what wrong or what i could try .thanks. just read another post sounded alot like this could it be a stater and would that couse charging proplems.thanks.

 

[Barnacle_Bill]

Re: 115 merc older cant get high rpm in gear

Check for a strong spark at all plugs. Yes, the stator can cause charging problems but the rectifier is the most common part to go. Test procedures for both is in your manual.

 

[halifaxboater]

Re: 115 merc older cant get high rpm in gear

thanks .bill i will test the spark in all plugs part of my winter overhall but cant seem to find a repair manual for motor checked at both boat shops by me but dont seem to intrested in helping me find a manual just want me to bring it in.

 

[Plainsman]

Re: 115 merc older cant get high rpm in gear

"i have aboat 132 psi on all cylinders except #3 96 psi witch is what it had when i bought it."

If I'm not mistaken, all cylinders should be within 10% of each other.

 

[halifaxboater]

Re: 115 merc older cant get high rpm in gear

your rite aboat the compresion i am taking a bit of a chance there . but did put over 100 hours on it this summer with out it changing witch surprised me pushing a 70 carlson,glastron 20 footer .thanks

 

[Chris1956]

Re: 115 merc older cant get high rpm in gear

You will want to post the year of that motor, or at least advise on whether is has 1 coil and a distributor, or six coils. There are different troubleshooting procedures for each type of ignition.

 

[halifaxboater]

Re: 115 merc older cant get high rpm in gear

it has the one coil one disdribuiter set up on it.i think its early 70s it has a serial number on the plate but not a year.thanks

 

[Plainsman]

Re: 115 merc older cant get high rpm in gear

With the serial # the year can be found

 

[Chris1956]

Re: 115 merc older cant get high rpm in gear

OK, Check for the spark arcing from the plug wires to ground, especially on the lower spark plugs. Examine all the spark plugs. If any of them are fouled, clean 'em up. If any of then look new, you likely have water intrusion in that cylinder. if they look OK, you might try pumping the primer bulb while running. If the motor runs at high speed, rebuild the fuel pump.

What pitch prop are you running on that motor? You need to be propped to turn 5500 RPM at max throttle. On that 20 footer, you likely need a 15" pitch prop of so.

 

[King mustang]

Re: 115 merc older cant get high rpm in gear

I had a problem just like that and it 1 of my carbs. had the float stuck. I took it apart and she been running smooth after that. I would also check fuel filters.

 

[halifaxboater]

Re: 115 merc older cant get high rpm in gear

it has an 18 pitch on it .before this trouble i could run about 37 mph at 4900 rpm at full throttle with it trim the best i could. i can get it to rev rite up in gear if its out off water with muffs but when in water .it wont. i pumped the bulb did not notice much diferance in it .but top carb .there was a little gas squirting out when motor was off and i pumped bulb just noticed.

 

[Chris1956]

Re: 115 merc older cant get high rpm in gear

4900 RPM at WOT is margional for those motors. It sounds like either your compression has dropped a bit not allowing the motor to get over the power curve for your boat, or more likely, you are dropping a cylinder.

Take a look at the spark plugs. Maybe you have a fouled plug, an arc over problem or water intrusion.

 

[halifaxboater]

Re: 115 merc older cant get high rpm in gear

thats what i thought at first but i did a test on all 6 cylinders and they were the same as when i bought it so im thinking electrical or gas .im going to put new wires plugs cap and redo carbs just for a winter project .and test the rest of elect.thanks