Spark Plugs

[Themanofsteel]

I have 1988 Force Outboard. I'm replacing the spark plug and the ends are black. What's the cause of this. See images. On a side note. I have a Bayliner Capri 17' with 85hp Force Outboard. How fast should my boat be able to go. I've never got it past 30mph. It does't have an RPM gauge.

 

[Jiggz]

That is some heavy carbon build up. You need to make sure you are using the correct fuel oil mix (50:1), correct fuel air mixture set correctly on all carbs (1- 1 1/4 turn out from lightly seated), and finally you need to decarbon your engine.

You can use either seafoam or power tune. Search the forum for other procedures used to decarbon. Note decarboning is not for everyone as if done incorrectly can cause catastrophic damage to the engine. If you're not sure you can do it just do the fuel treatment method, albeit it takes more than just one treatment hence takes longer.

For your boat type and engine, 30~35 MPH is about the max you can get depending on load, wind and water conditions, trim positions and prop type, size and pitch.

 

[jerryjerry05]

The speedo isn't the most dependable.
​When I drove a new 88 17ft. to a show.
It was pretty fast about 35-40 mph. Maybe faster.
Load conditions really affect these little boats.
You have trim@tilt?
What size prop?

You really need a tach to tell the running condition or performance.
E-bay sells them.
An item called a tiny tach can help, under 20$ E-bay or Amazon

Like Jiggz suggested do a decarb.
And reset the carbs.
The factory suggested that the 85's air screws be set at 1 turn out and left there.
Get new plugs

 

[Themanofsteel]

Thanks guys. Quick question on the decarbing. You pour seafoam in the gas tank right. How much? The capacity is 24 gallons I believe.

 

[Bkok33]

I saw you can get a gas can 3-5 gallons put the seafoam in that. Run it from the gas can, after its all in shut off the engine and wait about 15 mins then hook it back up to your tanks on the boat and run fresh fuel through it. Anybody correct me if I am wrong you guys.

 

[Jiggz]

Either way is correct although it may sound like you are speeding up the process by using a smaller fuel tank. But the fact is, using Seafoam (or powertune, PT) as fuel treatment requires a recommended standard proportion. If you use a small 5 gal tank then you use a less seafoam or PT to treat that amount of fuel. Or if you decided to use the in-tank 24 gal, then you use more of seafoam or PT to treat it. The only difference is that with the smaller tank you treat for a shorter time which may suffice or maybe not compare to using the 24 gals in tank.

Remember, the Seafoam or PT proportion has to be correct otherwise you can lose lubrication and knock out a ring or two. You can tell when your engine is decarb again easily with the looks of the plugs after each treatment run. Unless, you have a borescope that you can insert through the plug hole. And yes, a mini borescope for less than $20 will also suffice. They sell them at the bidding store.

 

[jerryjerry05]

My opinion!!! Sea Foam does NOTHING to remove carbon!!!
​Did a test with SF and Powertune
Had pistons from a rebuild.
Let 1 soak overnight in SF and 1 in PT.
The SF did NOTHING!!
The PT the carbon just melted away.

The SF might be good for absorbing water but does nothing for carbon.

PT in the throat of the carb as it runs.
Let it run and spray.
Shut off and tilt motor up.
Remove the plugs and spray a bunch of PT in the cylinders.
Turn the flywheel a bit and spray a bit more.
Let set 24-48hrs.

Start(gonna be tough) but get it running and install new plugs.

 

[Themanofsteel]

Question about decarbing with seafoam. How do I know when the engine is completely decarbed. Will the white smoke stop?

 

[Jiggz]

It will never be completely decarb but will surely lighten up the smoke and running smoother. To validate, clean the spark plugs after decarbing and then after running it for a couple of days, check them again. If they continue to have heavy fouling you are either not fully decarbed yet or you need to make some adjustments with the carbs' fuel mixture screws.

 

[Themanofsteel]

Jiggz Thanks.

 

[Simple_Man]

As for your speed, I have an 87 17ft capri bowrider with an 85HP, and a 17 pitch prop. I get 35mph on the GPS with a full tank and the Admiral with me. I also replaced the deck from the helm back. LOTS of heavy wet foam.