old mercury 1150 speed problems

[yamahoppermx]

i have been working on my 1976 mercury 115 hp outboard all summer.i finally got it running smooth. runs real good with ear muffs out of water,but when i put it in the lake last weekend and dropped the hammer all i got was a whopping 3 mph.any help would be much appreciated.thanks

 

[wcsd106]

Re: old mercury 1150 speed problems

What kind of RPMs are you seeing out of the engine? If you're seeing high RPMs but not going anywhere, you could have a spun prop hub.

 

[yamahoppermx]

Re: old mercury 1150 speed problems

i dont have a tach,but it revs real fast out of water and when its in the lake it just wont pick up any speed.

 

[yamahoppermx]

Re: old mercury 1150 speed problems

it moves in the water,just real slow.also it doesnt pick up rpm's like it does out of water.

 

[arsenalpsu]

Re: old mercury 1150 speed problems

you are missing spark on a few cylinders. Go buy an OEM shop manual and start reading to learn how to test the ignition system. Or bring it to a shop.

 

[yamahoppermx]

Re: old mercury 1150 speed problems

i have good spark on all cylinders.i have swapped cdi boxes,coils distributor caps,plugs,wires,checked timing and new rectifier.i have 2 motors with plenty of parts.i appreciate the advice but pretty sure its not a spark issue.earlier in the season i brought it to a machanic and they did work on it including cleaning the carbs.after reading some threads,i suspect it to be a fuel issue. maybe they just sprayed them with carb cleaner to make them look good?

 

[Chris1956]

Re: old mercury 1150 speed problems

Yes, The carbs will do that, as well as carb idle mixture. Try a bit of choke when you advance the throttle. If it then picks up speed, it is likely the carbs are dirty or the mixture is adjusted wrong.

If you think the shop cleaned the carbs, then open the idle mixture screw on the top carb 1/8 turn and retest. Follow with mid carb and bottom carb, testing after each adjustment.

BTW- You have achieved high speed with the existing prop? if you overprop these motors, they will not rev up.

 

[yamahoppermx]

Re: old mercury 1150 speed problems

wow.sometimes it is too easy to overlook the obvious.this morning i pulled off the front cover to get at the carbs.i was all set to take them off to clean them when i seen the linkage on the bottom two carbs wasn't hooked up to the top carb.i'm pretty sure three carbs will work better than one.thanks for everyones help and advice though.gonna get to the lake tommorow to test it out,wish me luck.