2002 Mercury 15hp 4 stroke

[Silverad04]

I'm having some problems with my motor. I've cleaned the carb, and replaced the fuel pump, filter, line, and plugs. It still seems to idle rough. When I take it out it seem to be bogging down at wide open throttle, only pushing my boat about 5mph. I thought it may be a spun prop, but I was running it in a barrel the other day, and the idle screw is backed all the way out, and not even making contact with the throttle. I've put a can of sea foam in the fuel, and it hasn't seemed to help yet(ran it for a couple hours). I did pull the plug after running it the last time, and the plug was wet. I don't know if that's normal? Does anyone have any ideas that can help me out?

 

[perchjerker]

really hard to say

are you sure you cleaned the carb properly? I think that carb has a welsh plug covering a mixture screw. Did you remove that when you did the carb?

I had the same motor years ago and I remember that plug is how I know about it

Might be the float is adjust too high

not sure if this is your carb but look at #38 in this pic. I don't know if this is the exact plug but the setup is similar. its there for emissions so you cant mess with the mixture but it helps sometimes if you can adjust it a bit

https://www.marineengine.com/parts/mercury-outboard-parts/15-4stroke/0g760300-thru-1b226999-usa/carburetor

 

[Silverad04]

really hard to say

are you sure you cleaned the carb properly? I think that carb has a welsh plug covering a mixture screw. Did you remove that when you did the carb?

I had the same motor years ago and I remember that plug is how I know about it

Might be the float is adjust too high

not sure if this is your carb but look at #38 in this pic. I don't know if this is the exact plug but the setup is similar. its there for emissions so you cant mess with the mixture but it helps sometimes if you can adjust it a bit

https://www.marineengine.com/parts/mercury-outboard-parts/15-4stroke/0g760300-thru-1b226999-usa/carburetor

Thanks for the response!! I don't know if I cleaned it properly, I'm a little new to this, but I do feel that I did a good job of cleaning it. Really the carb seemed pretty clean when I opened it up. I don't know what a nasty carb looks like to compare it to.

When I took it apart, I don't remember there being an adjustment for the float. Where would this be in the diagram?

I will have to look into that adjustment for #38, I'm not sure if that's my carb, but it looks like it. I'll try and get it started in the next week, and get back with you(mother/sister inlaw in town)

 

[perchjerker]

yeah there probably isn't a adjustment for the float now that I think on it.

on that plug, if you do find it, it is a brass plug that you can take a small drill bit and put a hole in the center and then screw a small sheet metal screw in it and use pliers to pop the plug off. there is clearance between the plug and the head of the screw but be careful. then you can get at the mixture screw, lightly seat it counting the turns so you know where to reset it after cleaning. Then you can adjust it, it only takes a small amount of adjustment to help

 

[crazymanme2]

You sure both plugs are firing?

 

[Silverad04]

You sure both plugs are firing?

No, to check that do I just pull a plug, leave it attached to the plug boot, and bump the starter?

 

[lovedr79]

My merc. 20 hp would do the same thing! On the water when it happened I tapped the float bowl with the handle of a screw driver. Got home pulled carb, cleaned all the gunk from ethanol fuel out. The float on mine was sticking closed. Never figured it out until the following spring when I was getting it out for the first time, I opened the drain screw, nothing came out, tapped the float bowl and magically the float fell down and fuel pour ed out.

 

[lovedr79]

You sure both plugs are firing?

No, to check that do I just pull a plug, leave it attached to the plug boot, and bump the starter?

Make sure the plug that is out is grounded on the head, bump starter or pull the cord, look for spark.

 

[wmk0002]

You sure both plugs are firing?

No, to check that do I just pull a plug, leave it attached to the plug boot, and bump the starter?

Make sure the plug that is out is grounded on the head, bump starter or pull the cord, look for spark.

You really need to use an air gap spark tester set at 7/16". Getting spark on the plug grounded to the head doesn't really tell you much.

 

[perchjerker]

it will tell you whether or not is it firing at all. If it is not you know you have an issue.

its not the best test for the strength of spark but its still useful information

at least it has been for me in my 20+ years of wrenching for a living

 

[Silverad04]

You sure both plugs are firing?

No, to check that do I just pull a plug, leave it attached to the plug boot, and bump the starter?

Make sure the plug that is out is grounded on the head, bump starter or pull the cord, look for spark.

When you say grounded on the head, how would I do that? Thanks for the help fellas!

 

[lovedr79]

Make sure it is touching a non painted stud or nut. Do not hold wth your hand. Usually you can sit it on there. Am air gap tester is the best and safest way. They don't cost too much either

 

[lovedr79]

Make sure it is touching a non painted stud or nut. Do not hold wth your hand. Usually you can sit it on there. Am air gap tester is the best and safest way. They don't cost too much either

 

[wmk0002]

it will tell you whether or not is it firing at all. If it is not you know you have an issue.

its not the best test for the strength of spark but its still useful information

at least it has been for me in my 20+ years of wrenching for a living

True. Got me there.

 

[turbotodd]

If the idle screw is backed all the way out and it still idles, it likely has an air leak somewhere. Suspect an o-ring or gasket between carb and intake manifold, or between manifold and cylinder head.

And by the way, the correct way to check for proper spark is to get a friend who doesn't know any better and have him/her hold the spark plug while you crank it.

 

[perchjerker]

it will tell you whether or not is it firing at all. If it is not you know you have an issue.

its not the best test for the strength of spark but its still useful information

at least it has been for me in my 20+ years of wrenching for a living

True. Got me there.

don't get me wrong, the spark tester is a good idea. I may get one at some point.

I can get a good feel for the strength of the spark just by looking at its characteristics, a bright blue spark with a "snap' to it indicates a strong spark, a weak yellow wimpy spark means there are problems.

But then I have been at this a long time

 

[Silverad04]

If the idle screw is backed all the way out and it still idles, it likely has an air leak somewhere. Suspect an o-ring or gasket between carb and intake manifold, or between manifold and cylinder head.

And by the way, the correct way to check for proper spark is to get a friend who doesn't know any better and have him/her hold the spark plug while you crank it.

I just ordered new gaskets for the intake, and both sides of the carb

 

[Silverad04]

Well, finally got the parts together. I replaced the needle valve, two gaskets on the carb, gaskets between the carb intake, and intake manifold last night. When I pulled the carb apart I noticed that the float was hitting the top of the carb as I had it upside down. I take it this means the needle wasn't closing. Would the needle not closing cause the problems im having? I haven't had a chance to run it, but I will SOON!!! It was idling on its own, but seemed to idle rough, and dogged down when I went about 50% throttle. I hope, I hope, I hope that was the problem....Tell me that was the problem!! :shock:

 

[Silverad04]

Well I was a little bummed at first, I ran the motor, and it was still running rough. I decided to replace the plugs, and started it up...purred like a walrus at idle!!! Only problem is It wants to die when I try to increase the throttle. If I wiggle the throttle back and forth, I can get it to go into the higher RPM's, but but it has a spot right above idle where it wants to die, any thoughts?

 

[Silverad04]