Merc. 140 sounds like a lawnmower

SSTKO81

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Recently took my 140 out for a spin. Ran great up to 2000 RPM then Sounded like a briggs and Stratton. -sounded like it was coming from the carb. -backed off the throttle and ran fine for an hour. -just sounds terrible and has no guts after 2k. Ever seen this before? Thought maybe a bad carb gasket...
 

QC

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Re: Merc. 140 sounds like a lawnmower

The real question is does it cut the grass?








:p Sorry. Couldn't help it :redface:
 

Don S

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Re: Merc. 140 sounds like a lawnmower

What have you done to it since it last ran ok, anything?
 

SSTKO81

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Re: Merc. 140 sounds like a lawnmower

What have you done to it since it last ran ok, anything?

Well, it will certainly cut pond grass....
When I put it up last fall it was making this noise. Took the intake off and replaced it because I found it to have a crack between the water jacket and exhaust plenum. -That seems to have helped, but obviously the problem is not fully cured.
I thought it could be detonation, but it seems to start and run fine at idle and low RPM, though it is a little shaky.
It's got new plugs, wire, cap, rotor, points and even the coil. Checked the timing and dwell; they're perfect...
 

Bondo

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Re: Merc. 140 sounds like a lawnmower

Well, it will certainly cut pond grass....
When I put it up last fall it was making this noise. Took the intake off and replaced it because I found it to have a crack between the water jacket and exhaust plenum. -That seems to have helped, but obviously the problem is not fully cured.
I thought it could be detonation, but it seems to start and run fine at idle and low RPM, though it is a little shaky.
It's got new plugs, wire, cap, rotor, points and even the coil. Checked the timing and dwell; they're perfect...

Ayuh,.... If it's goin' Lean,.... it'll detonate, 'n have no power, under heavier loads....
 

SSTKO81

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Re: Merc. 140 sounds like a lawnmower

Ayuh,.... If it's goin' Lean,.... it'll detonate, 'n have no power, under heavier loads....
Welll I'll try richening up the mix a little. -just a thought, guess a bad carb gasket would cause similar issues...
Gasket i've got on there is SUPPOSED to be reusable... :facepalm:And was reused after taking the intake off. I'll give it a shot and see what happens.
 

SSTKO81

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Re: Merc. 140 sounds like a lawnmower

Put a new carb gasket in and richened the mix but it still sounds terrible. Not holding idle very well either. I can set the RPMs at 1000, not touch the throttle and for no reason it will suddenly bog down to 400 and violently shake like its gonna die. -barely tap the throttle and it will shoot up to 1100 PRM and run fine. -still not making the briggs and Stratton sound till I get up over 2000 rpm
 

Don S

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Re: Merc. 140 sounds like a lawnmower

Your mixture adjustment is for idle only. Has nothing to do with 2000 rpm and above.
What shape is the plug wires in? When was the last full tuneup? Compression check, timing check. What year is your engine, is it points ignition?
If it is points ignition, hook up a dwell meter and see if it changes dwell at higher rpm.
 

SSTKO81

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Re: Merc. 140 sounds like a lawnmower

Last full tune up was last spring. And its got less than 4 hours on it since then. But just for giggles I put new plugs in and cleaned the arrestor a couple weeks back. The wires and points were replaced last spring and I've checked dwell at startup, but not sure how to do it at WOT. what would a change here indicate? I keep hearing detonation detonation, but I guess I don't know how to increase fuel in the upper RPM range...
 

Don S

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Re: Merc. 140 sounds like a lawnmower

I don't see detonation as the cause at this point.

Hook your dwell meter up and run the engine at idle, record the dwell. then raise the rpm up and check it. Should be the same.. Worn distributor bushings causes it, or week point springs.

Has it ever run right since you put new points in it?
 

achris

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Re: Merc. 140 sounds like a lawnmower

Start with a compression test... What's the compressions on each cylinder?
 

SSTKO81

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Re: Merc. 140 sounds like a lawnmower

I don't see detonation as the cause at this point.

Hook your dwell meter up and run the engine at idle, record the dwell. then raise the rpm up and check it. Should be the same.. Worn distributor bushings causes it, or week point springs.

Has it ever run right since you put new points in it?

yes, when I put the points in last spring i took it out and it ran like a cat on fire for about 2 miles out of the cove, then this "lawn mower noise" started happening and I lost my top end. I limped it back home and found the exhaust manifold to be cracked. -hasn't run right since.
 

Don S

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Re: Merc. 140 sounds like a lawnmower

The manifold is intake and exhaust. Have you replace it since you know it's bad? Have you checked the compression yet?
 

SSTKO81

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Re: Merc. 140 sounds like a lawnmower

Replaced the manifold and I've checked it thoroughly for leaks (visually and audibly). I haven't had a chance to do a compression check yet. -I'm hoping I'm not looking for a bad head or head gasket; the one bright spot here is that it's not overheating at all and there's no milk in the oil... I've considered maybe a valve or lifter may be off but that wouldn't account for only showing up at higher RPMs... I'll check the compression and put a dwell meter on it and let you know what I find.
 

stonyloam

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Re: Merc. 140 sounds like a lawnmower

Start with a compression test... What's the compressions on each cylinder?

I am with Chris on this one. Would not be surprised to see a bad cylinder or 2. You might try pulling the plug wires one at a time at idle to see if you have a weak cylinder.
 

SSTKO81

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Re: Merc. 140 sounds like a lawnmower

Took my boat to the mechanic; did a leak down test and found slight misfire on # 2 and no compression and # 1. So now we're pulling heads... This doesn't sound like its going to be fun... Or cheap.
Has anyone had a similar problem like this. Mech. Thinks its probably a bad valve (don't have results yet). What causes that?
 
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SSTKO81

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Re: Merc. 140 sounds like a lawnmower

result of this was cracked head between valves on #1. replaced head, gasket, one rocker arm and we're cookin' with napalm. thanks guys!
 

nola mike

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Re: Merc. 140 sounds like a lawnmower

Always nice to see a successful update!
 

QC

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Re: Merc. 140 sounds like a lawnmower

Yes ^^^^ thank you!
 
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