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Go Back   SailNet Community > On Board > Gear & Maintenance > Engines > Gas > Atomic 4 > Atomic 4 compression
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Thread: Atomic 4 compression Reply to Thread
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Topic Review (Newest First)
09-22-2011 09:05 AM
apogee1mars
Quote:
Originally Posted by fordo View Post
There is a quick and dirty compression test I learned from Moyer. Remove the spark plugs and press your thumb on the spark plug hole. Crank the starter. If you can hold your thumb there and no air leaks out compression is inadaquate. If air leaks out compression is ok. Low compression on adjacent cylinders is usually a bad head gasket. Is the crankcase oil milky? If so water is getting in the oil which is the head gasket, The exhaust manifold or a leak between the waterjacket and the crankcase.

If this happened after Irene the motion of the boat may have stirred up gunk in the gas tank causing proplems with the filter or carb. Definately get another mechanic
Much ta doo about little. The reality of the situation is that the head could be yanked off in an hour and taken to the local machine shop for all of the head work for cheap. A gasket set and some very basic hand tools and it would take longer to clean the bolt on parts then to re assemble. All top end work would be fresh no questions.
09-21-2011 09:39 PM
fordo There is a quick and dirty compression test I learned from Moyer. Remove the spark plugs and press your thumb on the spark plug hole. Crank the starter. If you can hold your thumb there and no air leaks out compression is inadaquate. If air leaks out compression is ok. Low compression on adjacent cylinders is usually a bad head gasket. Is the crankcase oil milky? If so water is getting in the oil which is the head gasket, The exhaust manifold or a leak between the waterjacket and the crankcase.

If this happened after Irene the motion of the boat may have stirred up gunk in the gas tank causing proplems with the filter or carb. Definately get another mechanic
09-21-2011 02:16 PM
emoney From the sounds of it, I don't think I'd be wanting a call back from that particular shop, let alone waiting for one.

The "she sits sometimes for a month or more at a time" comment is very telling. The A4 begs to be used and is most well behaved when she is. Today's Ethanol laced fuel is creating havoc in older engines, marine or otherwise, because they weren't built with seals and gaskets that were expected to be exposed to that. Couple that with the tough life they lead living in Saltwater most often, and you've got "issues" when left alone. Down here (Florida), I find it best to at least clean my carbs once every year and rebuild them at least every other year. When was the last time that was done on this particular unit? The fuel system hints have been good ones and you should follow those recommendations posted. I for one, would've assumed the entire fuel system was bad when they replaced the pump and had every inch of hose put in new. Good luck and I hope you get someone that can help get her back to chugging as nothing is more frustrating than spending all your time "fixing" and none "enjoying" the boat.
09-21-2011 01:12 PM
Hackettsan Thanks for all the feedback. My bet is fuel delivery as well, but the Marina refuses to call me back after diagnosing low compression.

I can't even get an estimate to tell me how much to properly diagnose.

To answer someone's earlier question, I am in Manhasset Bay in the Western Long Island Sound.

Looking for another mechanic.
09-17-2011 11:11 AM
apogee1mars
Quote:
Originally Posted by RichH View Post
Warning: the A4 has an UPdraft carburetor and its next to impossible to 'spray' into the carb. The updraft carb has a 'suction port' in the entrance throat of the 'flame arrestor' to prevent 'explosions' if this carb 'dribbles' fuel out of the carb and into the 'flame arrestor'.
I am pretty sure that spraying some starting fluid into the updraft carburetor will not create a significant hazard. I know that the infernal combustion engine can be a confusing item for many, but that is certainly not the case for all. If you would wish to dis assemble the intake system to apply some go juice, head on, but not necessary.
09-16-2011 12:52 PM
Minnewaska
Quote:
Originally Posted by Hackettsan View Post
......This is my first full season, and it has been a tough one!
Unfortunately, you will become very jaded about the quality and honesty of many, if not most, marine maintenance facilities. If you ever find a good one that you really trust, pay them whatever they want.
09-16-2011 12:50 PM
RichH
Quote:
Originally Posted by apogee1mars View Post
I'll second fuel delivery. Easy to find out. Just spray some go juice in the carb and see if it kicks.
Warning: the A4 has an UPdraft carburetor and its next to impossible to 'spray' into the carb. The updraft carb has a 'suction port' in the entrance throat of the 'flame arrestor' to prevent 'explosions' if this carb 'dribbles' fuel out of the carb and into the 'flame arrestor'.
09-16-2011 12:35 PM
apogee1mars I'll second fuel delivery. Easy to find out. Just spray some go juice in the carb and see if it kicks.
09-16-2011 12:30 PM
Minnewaska My money is on a fuel delivery problem. Possible it's either clogging or the switch mentioned. I will bet the compressions have been in their current state for years.
09-16-2011 12:18 PM
BubbleheadMd Lots of good info in this thread. Definitely go to the Moyer forum and discuss this.

But first of all, the A-4 is a low compression engine to begin with, and everything about it is heavy duty. That's what makes them so robust.

The stalling symptoms you describe don't seem to be compression related. An engine with relatively even compression across all cylinders, will run even if the compression isn't optimal. It sounds to me like the marina did a dry compression test and stopped investigating.

Your symptoms seem more fuel or electrical related. It could be a variety of inexpensive, and simple things:

Ignition points worn out, and/or mis-adjusted.
Condensor worn and failing.
Primary ignition coil failing.
Primary high tension wire from coil to distributor cap failing.
Distributor cap worn, or cracked.
Electric fuel pump not pumping (loose wire?)
Clogged fuel filter.
Clogged water/fuel separator.
Clogged carburator idle jets or main jets.

I've had several old cars (old Volkswagens and such) and when the ignition points get badly pitted or the gap slips closed, the symptom is exactly as you describe. Running fine, then quits, then fails to start or barely starts and dies.

Check your ignition point gap and file the points smooth if necessary, or just replace them, and check your distributor cap.
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