Spark Plugs may Indicate excessive exhaust back pressure

[congoboard]

The condition of my spark plugs may indicate excessive exhaust back pressure - they are black and oily looking. My question is how do I test this and what do I do about it if it is true ? Has anyone else been through this ? I am the 3rd owner of this 1978 Newport 30 with just 637 hours on it's A4.

[Dave Neptune]

Congoboard, yes it could and it could indicate a few other things as well :eek:.
My first question would ba how old is the exhaust? It could be the rings are not sealing well and oiling up the plugs, the idle could be way to rich and even bad or to much oil in your fuel.
Regarding back preassure has the performance fallen off slowly or somewhat rapid? The hours don't mean as much to the exhaust as the age does. It is common for the exhaust to plug up where the water is inserted into the exhaust stream. Usually replacing the hot section to the insertion point is all that is necessary. The Hoses can go for a quite a while however if you can see some of the wire comoing out of the casing it is probably time to replace as a hose colapsing on the inside is hard to determine.
Many times you can rev the engine and note the quickness and RPM then pull a plug wire and repeat, if it revs to more RPM and a bit quicker with a wire removed it is somewhat indicative of excessive back preassure.
Check to see if you have a small pipe plug in your exhaust flange, if you do it is for inserting a preassure gage to check back preassure.

Dave Neptune:cool:

[Dave Neptune]

Just noticed it was your first post so welcome to the Afourian Forum Congoboard.

Dave Neptune :cool:

[Maurice]

Hi,
A few things to check.
-have you noticed if the exhaust smells rich. The carb may require a mixture adjustment and / or need a good cleaning. That would be my first guess. You may see a slight sheen on the water also.
-is it using any oil...very unlikely culprit if all plugs are fouled. Number 4 is usually worse.
-are the plugs gapped correct...might want to try the hotter running plugs; for now clean the tips of the ones you have with some sandpaper.
-a good indication of back pressure problems is lack of power and can't get RPM up...that could also be the carb main jet partially blocked also.

Have a look at those things before you start on the exhaust. The problem is likely a combination of plugs and carb adjustment. Don't be afraid to take the carb apart. I take my apart each year and use the same gaskets to re install...no gasket glue etc to be used. Remove the jets, and lay in a small container. Soak with carb / combustion chamber cleaner. While jets are soaking spray down the rest of the carb. Remove float and needle valve carefully so as not to bend it...very easy to work on without hurting the adjustment. Spray everything liberally and the blow some compressed air through all passages and the jets. Put it back together taking care to keep parts clean.

Mixture adjustment....tighten the screw all the way in then back it off 1 1/4 turns. If you notice a rich smell out the exhaust back it off another 1/4...you do this until you can't smell the rich fuel. Go ahead and use the boat, next morning, when engine is cold it should start with choke and require the choke (or 1/2 choke) for the first minute of running. If that is the case it is pretty close.

Best I can do without cover-alls on ... LOL

[Maurice]

Mornín Dave,
You type faster than me for sure. Welcome aboard Congo...Dave is an excellent carb guy on here. So if he tells you more than I he is the one to be listening to.

[jpian0923]

What they said.

http://www.moyermarine.com/exhaust.htm