1996 Glastron 4.3l Merc I/O fouling plugs...

[Maverick27]

Hey gang! I love the site so far. Very helpful and nice people.

I have a 1996 Glastron GS 185 Fish n Ski. It has a 4.3l Mercruiser I/O. It ran like a champ for the last year I owned it and had just over 100 hours when I bought it. HOWEVER, I spent a couple hours trolling for trout at super slow RPM's. That seemed to be bad and fouled the plugs. It kept dying at idle and needed to pump the throttle in neutral to start it. I replaced the plugs and it started quickly on the next outting (even cold) and seemed to run great. BUT after trolling for a while, black smoke from behind the boat and the dying started again. It got so bad I could not even keep it running enough to get it on the trailer. I had to rev it and dump it into gear to get it going. It sounded like a minibike when it started.

So, I obviously fouled the plugs again, but what is the cause and how do I fix it? I have been told most likely a sticking choke or carb needs rebuilding. Any help would be appreciated. I don't want to spend time or money fixing something that is not the problem.

Also, sorry if this was covered before, but this site is huge and hard to find specific topics sometimes.

Thanks!

 

[JustJason]

Re: 1996 Glastron 4.3l Merc I/O fouling plugs...

If your litterly truely trolling for hours then you need to step up to a hotter plug.

At idle rpms the combustion chamber doesn't get hot enough to allow the plugs to get hot enough to be self cleaning, and that's why your fouling plugs.

If you do go to a hotter plug watch your WOT runs, 3/4 throttle is okay but try not to run at WOT for more than a few minutes at a time.

 

[Don S]

Re: 1996 Glastron 4.3l Merc I/O fouling plugs...

When was the last full tuneup?
It's hard for a carbed engine to slow troll for very long. Just giving it some throttle in neutral on occation will help clear it out.
Most people that do a lot of slow trolling just get a small outboard kicker for that job instead of wasting a larger engine for trolling all day.

 

[Maverick27]

Re: 1996 Glastron 4.3l Merc I/O fouling plugs...

Thanks guys! Both posts make sense. I used to use a trolling plate so my old boat would run at slow speed but higher RPM's. I was told last season when I bought it that it was de-winterized that week and gone through for my purchase. Part of the problem may also be that the lake I take it to every weekend has a 5mph limit on the WHOLE lake. So, I either troll or drive and anchor for a while.

So, if I'm reading you right...there may be nothing wrong with it and I should replace the plugs with hotter ones and either get a trolling plate or go easy on the trolling. I took the metal air cleaner off and cleaned it this time. Wasnt too bad , I could see light through it before I cleaned it. The choke seems to open and close freely.

So...

Hotter plugs (any model suggestions)
Tune up (what else for tune up)
Use a trolling plate or kicker motor
Anything else?

P.S. you guys are awesome and deserve huge props for the help and attention to detail!!!!

 

[Don S]

Re: 1996 Glastron 4.3l Merc I/O fouling plugs...

If you don't go over 5mp, you could probably get away with getting another prop (for that lake) that really underprops the boat something like going from a 19"pitch to an 11" (example) then you would have to use a bit higher rpm for slow. Just don't try to go wide open throttle.

 

[Maverick27]

Re: 1996 Glastron 4.3l Merc I/O fouling plugs...

I can probably do that. I'm sure since the two prior owners didnt even fish, they probably have a faster prop on it. I'm sure doing all of the above would be good. The only other places I take it to are the bay (5-10 mph) or bigger lakes, but those dont really need WOT either.

 

[Don S]

Re: 1996 Glastron 4.3l Merc I/O fouling plugs...

Keep your old prop, and change it when you go to the lakes were you can go faster.

 

[Maverick27]

Re: 1996 Glastron 4.3l Merc I/O fouling plugs...

Great idea. Any suggestions on a hotter plug?

 

[Don S]

Re: 1996 Glastron 4.3l Merc I/O fouling plugs...

Don't use a hotter plug till you see how it works with the smaller prop and get a full tuneup. If the plugs are fouled now, it needs new ones, and may need a carb adjustment. What rpm's are you idleing at when trolling?

 

[Maverick27]

Re: 1996 Glastron 4.3l Merc I/O fouling plugs...

around 850-1000 I believe

 

[Don S]

Re: 1996 Glastron 4.3l Merc I/O fouling plugs...

You also need to take that boat and run it at 3500 to 4000 for an hour or so to clean it out a bit, use some Seafoam in the fuel too. Those combustion chambers are just loading up with carbon, along with the spark plugs.

 

[Don S]

Re: 1996 Glastron 4.3l Merc I/O fouling plugs...

around 850-1000 I believe

Yeah, you probably need a complete tuneup and carb adjustment.

 

[JustJason]

Re: 1996 Glastron 4.3l Merc I/O fouling plugs...

5mph??? What a waste of a 4.3

All jokes aside. Just keep this in mind. Underproping to raise rpms and using a hotter than spec plug can both cause damage to a motor if you don't pay attention. If you do pay attention then you'll be just fine.

If you run a smaller prop, your trolling rpms will rise and the combustion temps will get closer to normal to help those plugs clean themselves. But if you try and take it to WOT then you will over-rev the engine, and possibly destroy it.

If you run hotter plugs, at lower rpms it will be fine. If you hold the motor at WOT to long the temps will be to high inside of the engine (not what you read on the gauge) and you'll detonate and have a meltdown.

Carbed motors don't like to troll as Don said. They get loaded up with unburnt fuel/hydrocarbons. Another suggestion would be to troll for 1/2 an hour, then put it in neutral and run the motor at 2500rpms for a couple of minutes, then on to more trolling.

This isn't meant to sound racist or anything like that, and please google it, but you need to give the motor an italian tune up every once in a while.

 

[Bondo]

Re: 1996 Glastron 4.3l Merc I/O fouling plugs...

Carbed motors don't like to troll as Don said. They get loaded up with unburnt fuel/hydrocarbons.

Ayuh,... I gotta Disagree with Don,+ JJ,...
With proper Tuning, my barge with it's 4.3l will idle trolling for up to 18hrs a day...

When I 1st dropped the 4.3LX into it, the smell of raw Gas at the transom was literally sickening...
Armed with the Street/Strip Carb Tuning Kit for a Carter AFB, which is a carbon copy of the Merc/ Weber, which is a carbon copy of the Edlebrock Performer,...
I Leaned the idle Way down,...
The factory settings were Extremely rich, which makes for less motor problems for Mercruiser, but didn't cut it for My application...

Tune the Carb,... Hotter sparkplugs might band-aid it, but could also lead to Holes in the pistons....

 

[Maverick27]

Re: 1996 Glastron 4.3l Merc I/O fouling plugs...

You guys are awesome! Seems like no "right" answer persay. I think I may adjust the carb and do the trolling plate and/or new prop. Especially since I almost never go WOT. In the event that I do, I will have advanced notice enough to change it back. I.E. plan trips to larger lakes or go outside of the jedi at my local harbor. I also may sell the boat and get a better suited fishing boat with a small 4 stroke motor that can do it all as far as fishing.

Thanks for all of the input. I will update as to what works and what I have tried. Happy boating!!

I gotta go with Bond-O on this one. Marine carbs are set to run rich at idle when tuned from the factory. In most siutuations, Marine engines don't spend a lot of time at idle so its not a big issue.

With that said, I think I would still look at a kicker or even an electric trolling motor. A case of the right tool for the job.

 

[JustJason]

Re: 1996 Glastron 4.3l Merc I/O fouling plugs...

Just curious Bill, what exactly did you do to the carb? I can't imagine your changing the main jet to fix an idle problem, or turning the mixture screws in to lean out the mixture, so how did you set it up?

 

[Bondo]

Re: 1996 Glastron 4.3l Merc I/O fouling plugs...

Just curious Bill, what exactly did you do to the carb? I can't imagine your changing the main jet to fix an idle problem, or turning the mixture screws in to lean out the mixture, so how did you set it up?

Ayuh,... Jets stay the same,.. Needles can be swapped out in a couple of minutes...
Bigger at the top needles lean the low speed circuit... Pointyer on the end, more fuel at wot...
Changing the springs control when it richens, or leans...

The "Kit" I've got has probably 8 or 10 sets of needles, a 1/2doz. spring sets,+ a variety of jets...

I just Love these ole AFB Clones...