Tower of power problem

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arsenalpsu

Petty Officer 1st Class
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Dec 1, 2008
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290
I have a 1984 Mercury 115hp I-6. I took it out for the last drive of the season, took a few laps and on my way back it lost power. Made it back to the dock slowly but would not accelerate, it felt like I lost a cylinder.

I pulled all 6 plugs and most looked ok BUT #2 had a pice of metal between the ground and center electrode. My question is could this piece of metal on the spark plug have grounded it so it wouldn't spark? What could have caused this? I plan to check compression this week, if it's ok what should I do to prevent this cylinder from getting any worse?

I have a fuel/water seperator and have replaced the impeller and always use stabilizer. I didn't hear any noises, no smoke, never stalled, just lost power. Assuming this metal caused the plug to stop firing, will the cylinder continue to degrade or was this just a lucky short?

Thank you, Jon
 
timmathis

timmathis

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Re: Tower of power problem

How big was the metal? Do a compresson check and repost?
 
A

arsenalpsu

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Re: Tower of power problem

It was just large enough to bridge the gap between the ground and center electrode on the spark plug. About twice the size of the head of a pin, pretty small. I'll do the test and get back......
 
A

arsenalpsu

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Re: Tower of power problem

ok I did the test:
1, 3,5,6~130
4-120
2-110 This is the one the plug was shorted out on. I know it was shorted,
tested and it showed curent from rear terminal to Neg side. I removed the
small piece of metal and it tested fine. (should i replace this plug?)

This being said i did not test it warm incase it would damage it further. I spraied some fogger into #2 and it went to 120, I'm thinking if it was warm it would probabaley hit 120s?

SO the question is was this just a random piece that broke off that happen to hit just the right spot on the spark plug to short it?? OR/AND is this an indication of a bigger problem? cooling, mix not rich enough, timing, ect???

Am I ok at this point?- any suggestions please.....

Thank you!!!
 
F

Fuzzytbay

Chief Petty Officer
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Messages
557
Re: Tower of power problem

Sounds like pre detination. Were you running at WOT? Generally there are no
spare peice's of metal in a cylinder. Chance's are its melted aluminum from the piston crown.
 
A

arsenalpsu

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Re: Tower of power problem

I agree, i think it's from the piston. As it still has compression is it ok or only going to get worse? What can i do about the pre detination?
 
A

arsenalpsu

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Re: Tower of power problem

I've been talking with some guys around where I live and have come to the concolusion that it was pre detonation which belew off a few pices of metal from the piston & fowled the plug. That being said what do you guys think about the below:

1. Its ok to run but keep an eye on compression, if it gets worse will need to
build?
2. Do a decarp with sea foam?
3. Check timing and make sure it's at 21 (i have never adjusted timing, how
do i go about this?)
4. Make sure I use good quality oil (i've been using cheep stuff from walmart
that from what i've heard can lead to carbon build up and pre detonation)
5. This happened when i was running with a full boat (6ppl) and was told
this can cause laboring and therefor pre detonation. I also use this boat
for skiing, is that still ok?

Thank you!!
Jon
 
J

Jeff_G

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Messages
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Re: Tower of power problem

Not all is lost. If it was just a small bit then you may be OK. It is not an unusual problem. Do the following;
Reduce your timing to 19* @ WOT
Go up one jet size in the main jet. It's in the bottom front of the carb.
Remove the air jet that is in the top of the float bowl.
Run a good quality oil, I love Mercury's Premium Plus in the inlines. Run for 10 hours at 25 to 1 oil ratio. You will build up some carbon on the eyebrow of the piston which is a good thing, it protects the piston somewhat.
Premium is preferred.
If I rebuilt every inline that detonated like yours I would have gone nuts!
 
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arsenalpsu

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Re: Tower of power problem

Jeff,

-I know there is that thred for timing and sync, but how exactly do I reduce
the timing to 19? I have never adjusted it or looked at that arrow by the fly
wheel.
-You said "premium is preferred", I'm assuming you mean gas, 89 or 91?
- When you say go up one jet size, is this something i must purchase or an
adjustment? (probably a stupid question but obviously I'm a rookie)

Thank you!!
Jon
 
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Jeff_G

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Messages
179
Re: Tower of power problem

premium fuel.
Yes you will need to replace the jet. They are small brass jets, carefully unscrew it. Once unscrewed they don't want to come out, use a toothpick and it will come right out.
Also If you have any modules, small black boxes the size of a deck of cards, take them off and throw them away.
Don't forget to remove the air jet from the float bowl cover.
 
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arsenalpsu

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Re: Tower of power problem

What part should i replace the current jets with?

For the modules, are you talking about the idle stabilizer? If so this it's located in front of the carbs right?
 
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arsenalpsu

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Re: Tower of power problem

Jeff,

it's gone....

For the lower jet replacement, i can order .076, .074, .072, .070, & .068, as I have no idea what this came stock with what size do you recommend?

You recommended to run it for 10 hrs at twice the oil, can I do this at idle on the muffs? And can/should I use my 50:1 mix of 89 gas and wallyword oil (to double the mix i will use the good stuff) or should I drain and replace with new 91 and all good oil?
 
1

17.5cobra

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Messages
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Re: Tower of power problem

Hey in regards to the jet size look at your old jet maybe with a magnifying glass there is a # on it that will give you a stating point for size.
 
F

Fuzzytbay

Chief Petty Officer
Joined
Jun 6, 2008
Messages
557
Re: Tower of power problem

arsenalpsu said:
Jeff,

-I know there is that thred for timing and sync, but how exactly do I reduce
the timing to 19? I have never adjusted it or looked at that arrow by the fly
wheel.
Click to expand...


Use a timing light, on number one cylinder, just as the link n sync say's, only adjust timing to 19, at MAx not 21.


arsenalpsu said:
-You said "premium is preferred", I'm assuming you mean gas, 89 or 91?
Click to expand...
Yes 91 octane, 89 might be ok, but since you have an issue, I'd run it on 91 first, if it seems ok after a tank or two, then drop back to 89, and 87 is a not ever fuel now.

-
arsenalpsu said:
When you say go up one jet size, is this something i must purchase or an
adjustment? (probably a stupid question but obviously I'm a rookie)
Click to expand...


I am not sure I would play with the jets, at least not now. Its more important to make sure the motor will run, without further damage. With the compression being 20lbs diffierent between best and worse. I'd try and figure out if you do need to rering, decarb, or rebuld.
 
turbinedoctor

turbinedoctor

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Re: Tower of power problem

Go ahead and up your jets one size, use only 91 octane fuel ever, you can add octane booster to your fuel in the tank if below 91, run some Sea Foam spray through the carbs to decarb real good. You may have a few rings starting to stick and decarbing may help loosen them up. These are cheap easy things to try before a rebuild. You may even try to spray some Sea Foam into the cylinders and let it soak for a while. On a personal note I only use Mercury 2 stroke oil and premium fuel in mine.
 
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arsenalpsu

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Re: Tower of power problem (update)

Re: Tower of power problem (update)

I did the timing adjustment this weekend. The first pickup was really messed up, about 8-9 so I moved it to 5. WOT while cranking was set at 21 so I backed it down to 18 and also removed the air jets on each carb cover. I let it run for a bit and #2 plug was nice and warm so it's firing. I did a compression check with a new gauge (i had a friends one before) after running and it only gave me 110 on a few and 90 on #2. With the other gauge I had 130 and 110 so I still have the same PSI difference but lower pressure overall. Not sure why, hoping the gauge sucks?

I was also told to increase the main jet one size, how necessary is this? The top two carbs wouldn't be to bad but the third would be very hard to get to, any suggestions?

Also, I've been told both ways, but do you guys think I should de-carb? Jeff said to run at 1:25 mix for 10 hrs to build up carbon on the piston crowns and others have said to decarb to try and increase compression....not sure which I should do?

Jon
 
F

Fuzzytbay

Chief Petty Officer
Joined
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Messages
557
Re: Tower of power problem

Its tough when you can't reach a concensus. Personally I'd just do a de carb using sea foam. I'd skip the 25:1 mix/ratio run time. There is no way to fix a damaged piston, except to replace it. So if the de carb works, great. If not adding carbon, to just burn off, doesn't seem to matter in this case. (potentially the 25:1 mixture could cause some leaning out too, making matters worse, unlikely, but possible.)If it was my motor, I'd want to figure out now, if I need to replace it. So try to see if the rings are stuck. If not, given the fact your still down 20 lbs on the cylinder, you need to find out if you can get some compression back. It may work out that the other cylinders show improvement, and the bad one doesn't. IF that senario turns out to be true, you maybe looking at a rebuild anyhow.
 
turbinedoctor

turbinedoctor

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Re: Tower of power problem

I'm with Fuzzy on this one, building up carbon is creating a problem to cover another problem. I would do the de-carb to try to unstick the rings and maybe increase the compression. While trying to clean my pistons during my rebuild, I found that GUNK engine cleaner seemed to do an ok job on the carbon but was still a little slow. Don't know if I would shoot any into the cylinders but I would shoot some Sea Foam in there and let it soak a while.
 
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