1980 Mercury 80 HP 4 cylinder hesitation...

[pubnicobob]

Motor in great shape...rebuilt 15 years ago, used little and babied when it was. Never any trouble until this summer. Starts good, idles good, top end is normal...but usually after motoring along for a period of time at <2000 RPM, when you try to plane off, there is a hesitation at around 2200 RPM. Sometimes the motor seems to recover and speeds up normally...and other times it just seems to pause at 2200 RPM and will stall if not throttled back. Seems to only happen after the motor has warmed up. Fuel filter was just cleaned. Any quick things I can check before it has to go to the shop? Thanks!! PB

 

[pubnicobob]

Re: 1980 Mercury 80 HP 4 cylinder hesitation...

?????

 

[tredragon]

Re: 1980 Mercury 80 HP 4 cylinder hesitation...

I have a similar, if not the same problem. Throttles up fine in Neutral but won't throttle up in either gear very often... Once it's running at higher RPM's though it purrs like a kitten, starts OK... I've read a few threads and see the words "spark" crop up a lot. I might have to check plugs, coils, etc.

 

[tredragon]

Re: 1980 Mercury 80 HP 4 cylinder hesitation...

okay, so don't know if this will necessarily apply to your situation but my friends here recommended in my thread to check idle speed and mix. if you take the wraparound cover off the powerhead, you'll see a few bolts with plastic caps on them. they are usually labeled, my reco was to adjust idle mix 1/2 turn counter clock to richen up the mix. i'm going to try this with the muffs on and see if she throttles up in gear better.

 

[pubnicobob]

Re: 1980 Mercury 80 HP 4 cylinder hesitation...

Thanks tredragon....but I don't think I need to adjust anything, because it doesn't always do it. It seems to happen after the motor warms up, and especially after running along slowly (<2000 RPM) for an extended period of time. Somebody told me I might have a reed valve problem. Do these stick intermittently, or? Don't know anything about them.

 

[TommyA]

Re: 1980 Mercury 80 HP 4 cylinder hesitation...

It would be a easy test and would eliminate one easy to make adjustment to adjust the idle mixture screw out like tredragon mentioned in his post before doing a major disassembly of the engine to replace reed valves. Just a thought you might try!

 

[pubnicobob]

Re: 1980 Mercury 80 HP 4 cylinder hesitation...

Thanks Tommy....I'd agree, but I don't like making adjustments for the sake of "trying something". This is an intermittent problem, so it seems to me that something is plugging or sticking.

 

[imported_Voyager]

Re: 1980 Mercury 80 HP 4 cylinder hesitation...

Have you tried squeezing the bulb?

It's possible that you have a fuel issue. I think the diaphragm fuel pumps are a bit marginal, especially at low speed. Perhaps after going slow for a bit, the bowls are getting low and the motor is starving when you throttle up...

It could be time to rebuild the carbs, or at least the fuel pump part of the carbs.

 

[pubnicobob]

Re: 1980 Mercury 80 HP 4 cylinder hesitation...

Turns out it was just sticky reeds from improper winterization. Problem worked itself out with no intervention. Thanks!