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Acceleration problem 1980 Merc 115

S

scottr

New member
"1980 Merc 115 has recently st

"1980 Merc 115 has recently started hanging up at about half throttle (~2000 RPM) while accelerating. I wouldn't describe it as "bogging down," more like something is sticking and it kind of sputters and knocks for a bit if I hold the throttle in that position, and then eventually kicks in and continues to accelerate normally. If I try to advance the throttle before it "kicks in," it dies. Otherwise it's running fine at idle and WOT.

My first thought was something was binding in the spark advance system because of the subtle knocking and the way it eventually "breaks loose" and smoothes out. Any thoughts on this behavior being ignition vs. fuel related and what to test?

If it was caused by insufficient fuel flow it doesn't seem like it would exhibit such a distinct change between sputtering and then suddenly flowing again. But could it be a float or valve sticking?

As an aside, there are two grease fittings on the distributor. I've lubed the lower fitting until grease comes out of the collar above it but I'm not sure what to look for if greasing the upper fitting (distributor shaft?). It seems to be taking a lot of grease. The shop manual has nothing about it. Suggestions?

Thanks,
Scott"
 
"Scott it does kinda sound lik

"Scott it does kinda sound like a fuel starvation problem - maybe carb related. When was the last time the carbs were pulled/cleaned/adjusted. If not in the recent past that would be a good place to start.

Problem may be related to clogged/partially clogged jet...

However, first check the easy stuff. Fuel tank (especially pick-up - may have crud in the tank and on initial increase in throttle, getting sucked against the intake screen).

Ditto the fuel filter, water separator (if equipped) - check the lines and connections.

But in the end, a clean carb sure doesn't hurt in any event..."
 
Here we go blaming the carbure

Here we go blaming the carburetors again.Put a timing light on this thing starting with cylinder #1 and observe the flash as you speed up.Repeat this with the other 5 also.Take notes and compare the flashing as the motor stumbles.This will tell whether it is ignition or fuel!!!!
 
"may be way off base on this,

"may be way off base on this, but the spark advance on my mariner L-6 had a stiff spot where it should have rotated smoothly, and this is what happened ( figured it out after new swithcboxes and pulling the flywheel) Corrosion had pinched a nylon bushing that held a pivot. good luck!"
 
I have a 70 hp merc. outboard

I have a 70 hp merc. outboard I think it is 1979
model year. When I hit full throttle it takes off and then the rpm's jump up but the boat doesn't go any faster. It sound as if the is something slipping. Could this be the sliding clutch assemble? Any help would be great.
thank you
new at boating
 
"Probably not a slipping clutc

"Probably not a slipping clutch. The lower unit doesn't work that way.

The first thing I would investigate would be the prop itself. The prop is a couple of separate components. There is a hub, surrounded by a rubber (sleeve) that is then pressed into the propeller itself.

Over time due mostly to sun damage (or the odd hit on the bottom) the rubber sleeve wears out so the prop begins to slip on the hub as the friction is lost.

It normally shows up first at top end, when the most "stress" is put on the prop.

If you have a spare prop you can swap them out and see if corrects the problem. If not you can put two adjacent marks on your prop. One on the hub (close to the splines) and one further out on the prop itself. Take it out for a spin and after you notice this "slip", check the prop. Marks out of line = spun hub."
 
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