merc 115 revs up but no go Please help

[GLASTRON007]

I have a 1994 pos merc 115 when I bought it the reverse never worked had a local mechanic look at it he said the foot wasent worth fixing, so I ran it all last season with no reverse the last time I took it out the whole foot quit working it would go in gear but no matter how much throttle it dont go but idle speed. I got a new foot and put it on.Seemed to work fine took it out sat. same thing the motor will rev up but wont go but idle speed no matter if its foward or reverse. Please help hopefully its a easy fix

 

[arsenalpsu]

Re: merc 115 revs up but no go Please help

sounds like you lost spark in one or two of your cylinders. Check compression and for spark, if it's compression than you need a rebuild- or if lucking you have a stuck ring- do a good decarb (all must be +/- 15% of eachother) If your missing spark from any of the plugs get an OEM manual and start to look at coils, switch boxes, stator, etc.

 

[GLASTRON007]

Re: merc 115 revs up but no go Please help

I dont think its spark,I think its loosing momentum between where the motor meets the shaft to the foot. The motor sounds fine runs on the hose fine but soon as there is pressure on the prop it seems to not run

 

[The_Kid]

Re: merc 115 revs up but no go Please help

Sounds like you may have a bad hub in the prop. When mine went out I had some thrust at idle, but when I gave it more gas the hub would just spin and I wouldn't go any faster.

You can check the hub by drawing a line from the center of the prop to the outside. If it's spinning the lines won't line up after you give it some gas.

 

[arsenalpsu]

Re: merc 115 revs up but no go Please help

I dont think its spark,I think its loosing momentum between where the motor meets the shaft to the foot. The motor sounds fine runs on the hose fine but soon as there is pressure on the prop it seems to not run

Loosing momentum?? Dude that makes no sense and if you know what it is why bother us with a question? If the hub was spun than you're RPMs would go up but the boat would not go. From what you said it reves up on muffs but not in the water so yes when there is pressure on it she does not speed up. That means you are not getting power from some of your pistons and YES it can seem like it runs well on muffs. You need 3 things for a boat to go, gas, spark, and compression. I'd bet it's either spark or compression that you're lacking, but i'd bet on spark.

 

[Moody Blue]

Re: merc 115 revs up but no go Please help

A little unclear what the OP is trying to describe. I'm interpreting it as a spun prop.

When the new lower unit was installed, was the old prop used or a new one? If the old prop, then no doubt it is a spun hub. If a new prop, then I would be looking at the powerhead.

 

[sschefer]

Re: merc 115 revs up but no go Please help

Could be the prop wasn't put back on correctly after the l/u change. Probably left the thrust washer out, didn't seat if fully, put the insert in backwards, etc.

However, there is one other distinct possibility. You bought a new prop and got a left hand instead of right or the new l/u is a lefty and you're running a right hand prop.

 

[arsenalpsu]

Re: merc 115 revs up but no go Please help

I don't see it being the prop.....he had this issue before he changed out the old LU and when he put on the new one the same thing happened. IF he had this issue only after changing to the new LU I would suspect a prop problem. But he only changed the LU b/c this issue started first out of the blue....check the prop as that's easy but my money is still on spark or possibly fuel....

Did you only change out the old LU because you though it was the original problem?? (Especially since the reverse didn't work you though the forward had taken a crap too?)

 

[sschefer]

Re: merc 115 revs up but no go Please help

Go back and read the first post. First it was no reverse then with the new L/U it only runs at idle speed even with the engine reved. That's not a spark problem. That's a power delivery problem.

If it's not a screw up at the prop then the only thing left is a stripped crank shaft.

 

[arsenalpsu]

Re: merc 115 revs up but no go Please help

......

so I ran it all last season with no reverse the last time I took it out the whole foot quit working it would go in gear but no matter how much throttle it dont go but idle speed. I got a new foot and put it on.Seemed to work fine took it out sat. same thing the motor will rev up but wont go but idle speed no matter if its foward or reverse. Please help hopefully its a easy fix

The way I read this it quite on him with the old (or original) LU still on...he then changed the LU thinking the old foot had gone bad.......GLASTRON, PLEASE CONFIRM OR CORRECT ME.

BUT i may have read one part wrong, is it reving up on muffs and in nutral OR do you shift it in gear and it revs up but the boat doesn't move much? I was thinking he got the RPMs up on muffs but when he shifts and hits WOT it would stay low RPM. IF he's getting 5000 RPM (very bad out of gear i know) when shifting into forward then i'd agree it's the prop......Glass, did you hit anything last time out with the old LU when she quite?

 

[CharlieB]

Re: merc 115 revs up but no go Please help

I dont think its spark,I think its loosing momentum between where the motor meets the shaft to the foot. The motor sounds fine runs on the hose fine but soon as there is pressure on the prop it seems to not run

I think he spelled it out here,

'Sounds fine on the hose, BUT.......soon as there is pressure on the PROP it seems to not run'

Classic symtoms of dead cyl(s)

Ignition or carbs.

 

[arsenalpsu]

Re: merc 115 revs up but no go Please help

my thoughts exactly.......

 

[Reg312]

Re: merc 115 revs up but no go Please help

Pull your prop and check your hub. Easy to do. Your symptoms are EXACTLY what I had last year. Put on a new prop and ran perfect.

 

[Moody Blue]

Re: merc 115 revs up but no go Please help

Too much speculation. Where is the original poster? We need more/clearer info to make a proper diagnosis. I stand by the "spun hub" diagnosis

 

[arsenalpsu]

Re: merc 115 revs up but no go Please help

LOL, I think I agree with that too!