Rich,

The flame arrestor is the metal screen (for a lack of a better term)that fits over the air intake of the carburetor. Its purpose is to do exactly what its name implies, that is, to arrest or stop flames from coming out of the carburetor in the case of a backfire.

Backfires can occur for a couple of reasons. If the intake valve stays open because of an improperly timed engine or if the valve actually sticks open -- if the air/gas mixture ignites while the valve is not fully closed the exploding air/gas will follow the path of least resistance and come out of the carburetor.

The Atomic-4 does not have an air filter...just the flame arrestor.

For a quick compression check just remove each spark plug and put your thumb over the hole. Have someone crank the engine over a few times. The compressed air should force you thumb off the hole. If it doesn't, then we know we have a problem.

To perform a more scientific compression test you'll need a compression gauge, which you can either borrow from someone who has one, or purchase from an Auto Supply Store such as PEP BOYS or some such. Get one that screws into the spark plug hole rather than the "rubber stopper" kind.

To perform a proper compression test:

Remove the ignition cable wire from the coil to the distributor. (This is done to prevent the possibility of an electric shock while performing the test.)

Just to be safe, mark the spark plug wires with a permanent marker or attach a label indicating which cylinder they go to. (This is to avoid putting the wires back in the improper order. The proper firing order should be 1-2-4-3.)

Before removing the spark plugs make sure to remove any loose dirt, paint, or rust from around the spark plug hole. (This is done to avoid getting dirt into the cylinders.)

Remove the spark plugs.

Screw the compression gauge into the first spark plug hole.

Turn the engine over couple of revolutions. (You can use the starter or the hand crank it if you have it.) You should see the meter on the compression gauge rise.

Record the reading on the compression gauge. (Example Cylinder 1 = 90lbs.)

Repeat the procedure for all 4 cylinders.

The compression readings should range from 85lbs to a little over 100lbs. The original design specification called for 95lbs.

At this point I am thinking your best bet is to borrow or purchase a copy of Don Moyer's Atomic-4 Servcie and Overhaul Manual. It costs about $50.00, but it will be the best $50.00 you'll ever spend on your engine. You can order it on-line at www.moyermarine.com .

I would also to go Sailnet.com and join the Atomic-4 email list. It is by far the best source (other than Don Moyer) for information regarding the Atomic-4. There are some real experts there and it is a very active list.

NOTE:

IF YOU ARE IN THE WATER -- BEFORE YOU START CRANKING THE ENGINE A LOT, MAKE SURE TO SHUT OFF THE COOLING WATER INTAKE VALVE. OTHER WISE YOU COULD GET WATER COMING BACK INTO THE ENGINE FROM THE EXHAUST SYSTEM.

The engine uses the exhaust gases to force out the cooling water from the exhaust system. Without the engine running...no exhaust gases to force out the water. Then water will back up into the engine. Not a good thing!

If you have basic compression (finger over the hole test) and spark. The next thing is fuel.

Don Moyer says:

"It is common for the throat of the carburetor to have fuel puddling in it if the choke is pulled (as it should be) for starting after a few seconds of cranking. However, even if there is fuel puddlng in the throat of the carburetor, you still have to have the choke pulled for easy starting.

One of the easy ways to determine of you do have fuel is to simply look into the throat of the carburetor... If there is fuel puddling in the carburetor, I usually make the assumption that the problem must be ignition."

If there's no fuel in the throat of the carburetor we have to find out why not. First, make sure there's gas in the tank. Then disconnect the fuel line from the carburetor and see if gasoline comes out when you crank the engine over. (Before cranking, put the end of the fuel line in a clear jar so you don't spray gas everywhere. Collect a sample of gas - approximately an inch or so in the jar.) The gas should be golden in color and there should not be any water (clear fluid) at the bottom of the jar. If there is water in the fuel we may have found your problem.

I think this is enough for now.

Let me know what you find out.

DON'T FORGET, JOIN THE SAILNET E-MAIL LIST!

Good Luck,
Steve