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Old 05-31-2011, 11:40 AM   #1
Ifishing_Viktor
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Default 4 stroke 15hp mercury won't idle...

Hello,

This is my first boat and motor so total newbie here. I'm mechanically inclined but it has been a long while since I looked/troubleshot a carb motor. Basically the motor runs fine under mid-full throttle, but won't start at low throttle and it won't run at low throttle, just sputters and dies.

Is this a common issue? Carb needs to be replaced? Or the gas filter? I'm guessing this is a 10 year old model. It also likes to be chocked up for quiet a while.

Thanks,
Viktor.

oh, anyway to make these things run quieter too?

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Old 05-31-2011, 12:17 PM   #2
fishkisser
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doh Re: 4 stroke 15hp mercury won't idle...

Clean your carb and the fuel pickup on your tank and replace all filters ...
If you want it to run quieter ... get a Yamaha ...
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Old 05-31-2011, 12:21 PM   #3
Ifishing_Viktor
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Default Re: 4 stroke 15hp mercury won't idle...

Quote:
Originally Posted by fishkisser View Post
Clean your carb and the fuel pickup on your tank and replace all filters ...
If you want it to run quieter ... get a Yamaha ...
hahaha, the yamaha comment was expected Thanks for the tip, i will do some cleaning then.
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Old 06-01-2011, 06:15 AM   #4
Smj
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Default Re: 4 stroke 15hp mercury won't idle...

Adjust idle/air mixture screw....Turn in to gently seat while counting turns. Unscrew to original setting. Run in water, in gear to fine tune, while adjusting idle/air mixture screw AND idle speed screw. If that won't work for ya' then you may need to dissasemble and clean carb....New gaskets,needle,seat etc. Do a serch using "motor won't idle" "Kicker idle", things like that, there's been a ton written on the issue.

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Old 06-01-2011, 08:42 PM   #5
Ifishing_Viktor
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Default Re: 4 stroke 15hp mercury won't idle...

Quote:
Originally Posted by Smj View Post
Adjust idle/air mixture screw....Turn in to gently seat while counting turns. Unscrew to original setting. Run in water, in gear to fine tune, while adjusting idle/air mixture screw AND idle speed screw. If that won't work for ya' then you may need to dissasemble and clean carb....New gaskets,needle,seat etc. Do a serch using "motor won't idle" "Kicker idle", things like that, there's been a ton written on the issue.

Smj
So are gaskets a must when cleaning a carb? they do have some residue on them but i figured it would clean right off. Any good place to order these things online? I need fuel filter, oil filter & gaskets. Or is there a local place to get these parts?
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Old 06-01-2011, 08:42 PM   #6
dinofun
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Default Re: 4 stroke 15hp mercury won't idle...

There is a long brass tube in the carb that has a bunch of holes drilled into the sides of it, I can almost garantee that the hole that runs the length of the tube is clogged. I've had this happen several times on mine (i blame ethanol) the hole is really reaally tiny probably a human hair thickness. I don't know what you can use to clean that hole but I've taken a strand of copper wire from some 12 guage stranded wire and keep pushing it in there until it goes all the way thru.
Runs like a top after cleaning. I think its part of the idle circuit in the carb(?)
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Old 06-02-2011, 06:05 AM   #7
Smj
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Default Re: 4 stroke 15hp mercury won't idle...

Quote:
Originally Posted by Ifishing_Viktor View Post
So are gaskets a must when cleaning a carb? they do have some residue on them but i figured it would clean right off. Any good place to order these things online? I need fuel filter, oil filter & gaskets. Or is there a local place to get these parts?
I only say new gaskets because if there were an air leak that would cause a lean condition at low idle even though the motor may run well ay higher RPMs. To get your motor down to the LOW idle you want, the mixture needs to be a bit richer with fuel than what a factory setting would be, that's one way they get the "CARB 2 or 3" rating, having the motor running super lean....And then 10% alcahol causes it to be even a bit leaner.

I've been working on small engines pretty much since out of high school. I will re-use gackets that look good, and sometime even torn a bit. A thin film of silicone sealant will work, but there's also a chance of causing even worse problems if you use too much sealant. That's why I suggested getting all new gaskets, but if you're mechanicly inclined you could maybe get away with using the old gaskets.

I would say to try the adjustment suggestion FIRST, and if that won't work then the info dinofun gave would be my next step.

To qualify, I've got a Merc 9.9 4-stroke (kicker) that is ten years old. I only run it 8 or 10 trips trolling for springers, and a bit in the summer and fall on the Columbia. It hangs on the stand in the garage from mid September untill March. I've never needed to get into the carb, only an adjustment before the season and maybe one during. I use a water separating fuel filter for both motors that are changed yearly.

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Old 06-02-2011, 07:53 AM   #8
EpicDay
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Default Re: 4 stroke 15hp mercury won't idle...

I have the same motor (2001) and also suggest to start with air/fuel ratio adjustment screw. The adjustment is located on the side of the carb above the bowl. As a starting point - tighten the screw and then back off 3-1/2 turns. The best method is to adjust the ratio when the motor is idiling under load (in the water.) I usually adjust the ratio with the motor running in the driveway with the flusing connection. It is very noticiable when you hit the sweet spot in the adjustment - the motor will purr at low rpm.

Regarding the parts - Mercury offers a carb kit that includes all of the typical gaskets, filters, and parts that need replacing. I purchase mine at Stevens Marine.
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Old 06-03-2011, 04:34 AM   #9
tt3886
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Default Re: 4 stroke 15hp mercury won't idle...

FYI,

Some discussion between the boat doc and myself.

He was right.

I missed it on my first go around with the carburetor.


Quote:
Originally Posted by tt3886
Doc,

- I've got a 2005 Mercury manual start 15hp 4 stroke kicker, that started acting up yesterday.

- Basically it won't idle, and anything below approximately 2000 rpm will result in it stalling unexpectedly (in gear or out).

- It's been idle (stored) for the last 3 months.
- Stored w/Stabil and ran dry.
- Yesterday (03/16/2011) was first start up.
- Start up was it's usual cantankerous self....creation of new cuss words.
- Let it warm up at high rpm, thinking that was all it really needed.
- Then trolled on the main all day, because that wasn't all it "really needed".

- Got home, and pulled the plugs. Looked ok.
- Pulled the carb/jets/float/needle..etc. Looked ok, but blew everything out with carb clean/cda, and reassembled.
- Started motor, but with same results.
- Pulled the fuel pump diaphgram and inspected. Looked ok...whatever that means.
- Replaced the in-line filter before the fuel pump.
- Primer bulb feels good, and appears to be working correctly...after carb disassembly/reassembly, it primed the carb with no issue.

Started motor, but with same results.

Any other suggestions?

The idle mixture screw needs to be accessed and removed and ensure the idle tube is clear. I would guess it's plugged
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