Sooty plugs

[crc21751]

I have a 1977 Pearson 28 and I'm the original owner. I originally had a raw water cooled A4 engine and recently installed a Moyer Marine long block which might have 75 hours on it. The problem is that I've been continuously fouling all 4 plugs since installed. It'll run fine for awhile (5 hours or so) then the plugs start to foul and then the engine won't accelerate. Virtually everything on this engine is new except the fuel tank and water lift muffler. My question is this: After numerous acid flushes and several rebuilt exhaust risers on the old engine, is it possible that the original water lift muffler is full of metal chips and rust to the point of creating excess back pressure?

[Maurice]

CRC,

Can you take a picture of the plugs with a digital camera. If all 4 are fouling I would first look to the carb. It might need to be leaned out a bit.
-do you notice a rich exhaust smell and
-do you see a light sheen on the water after the exhaust water hits it.

...if so, I'd look at the carb first.

[jpian0923]

What do you see coming out of the back of the boat? Normal flow?

[hanleyclifford]

Not only the water lift but also the hose leading to the transom should be investigated. Possible partial collapse of the inner wall of the hose?

[crc21751]

I'll take pictures of the plugs and post. I'm going to test the back pressure at the exhaust flange, as that is this problems low hanging fruit and once eliminated, I'll focus on fuel mixture. I'll probably need some advice on how to "lean-out" the mixture.

[Dromo]

Hi , just a thought .You might want to check your running temp. If your a-4 is not running up to temp , I would think it would foul the plugs. Try adjusting the bypass valve if you have one.

[Marian Claire]

Are you using oil? If the engine has not been running at a high enough temp the rings may not have seated yet. I ran mine to cold after I rebuilt it and the plugs fouled even after 75 hrs. I treated with MMO and began to run at the proper temps and within a few days she was fine. No more fouling and no more oil use. More likely it is one of the other ideas already posted. Dan S/V Marian Claire

[Bigeye]

Or.....check the timing, distributor, points, etc. and wires. May be uneven spark.

[crc21751]

Dromo: Engine temp is fine @ 180 on a fresh water cooled system.
Marian: I do not use MMO in my engine and that may be an issue. I found that when I ran at full throttle the plugs were a nice gray color but at idle or slow speeds they fouled quickly. I changed to high octane fuel and hotter plugs (from RJ8s to RJ12s) in the hopes of getting a hotter burn but still fouled a low speeds.
Bigeye: Timing seems to be OK but I'll add that to the list and check after the back pressure.

[smosher]

Sure sounds like the low speed mix needs to be leaned out a bit.

A good starting point would be 1 1/2 turns from closed, The adjustment is an air bleed which means as you open the screw, more air is intoduced into the low speed jet which leans it out.

I check to see if its too rich by the transition from idle to power, if it stumbles
its too rich.

Steve

[hanleyclifford]

Sure sounds like the low speed mix needs to be leaned out a bit.

A good starting point would be 1 1/2 turns from closed, The adjustment is an air bleed which means as you open the screw, more air is intoduced into the low speed jet which leans it out.

I check to see if its too rich by the transition from idle to power, if it stumbles
its too rich.

Steve And if you get a loud, sharp "pop", it is too lean.

[sastanley]

Don't waste money on high test fuel...the compression ratio is 6.5:1 on this motor.

I'd check the timing first..make sure the advance springs are operating properly (although you report things are OK at high RPM.)

Are you "using" any oil??? i.e. are the plugs fouling from burning oil? I rebuilt a motor for my 1991 Civic and it took a lot longer than I expected for the rings to seat and the motor to stop consuming oil (like several months, and several thousand miles) 75 hours should be enough, but who knows? :confused: