Hi mates, having some troubles with an Atomic four cylinder gas engine, 20 - 25 h.p. it starts easily, goes into gear no problem, but when given a bit of throttle will die or if let to run, idle for a few minutes it will die. Good compression, it starts easy. Just put an electric fuel-pump in. Changed the fuel filter and fuel line. Getting plenty of fuel to the filter. Any motor guys have an idea?
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Carbon in muffler.
I had the same problem a few years ago. It turned out to be carbon build up in the water lift muffler. Too much back pressure.
I had the same problem a few years ago. It turned out to be carbon build up in the water lift muffler. Too much back pressure.
carb float
I had similar problems, and a leaky carb float turned out to be the culprit. The float was a hollow metal bulb, kind of like the float in a toilet tank, but of course smaller. Turns out it had a pinhole. Start the engine, runs fine, float is floating like its supposed to. But slowly it fills, sinks, shuts off fuel. Sitting unused for a week, the float dries out, whole baffling process starts the next time. When I finally checked the float, the pinhole was visible, and the mystery solved. This was, what, 1981?, when engines still had carbs, floats, points. I went to the local Mr. Carb shop, and amazingly they had a used A-4 carb sitting on the back shelf. As I recall, the replacement carb had a foam float, so couldn't leak like the old one. (And if yours has a foam float, there goes my theory.) Good thing they had one in stock, he told me, or I'd be waiting weeks to order one. Can only imagine what the wait would be now. --paul
I had similar problems, and a leaky carb float turned out to be the culprit. The float was a hollow metal bulb, kind of like the float in a toilet tank, but of course smaller. Turns out it had a pinhole. Start the engine, runs fine, float is floating like its supposed to. But slowly it fills, sinks, shuts off fuel. Sitting unused for a week, the float dries out, whole baffling process starts the next time. When I finally checked the float, the pinhole was visible, and the mystery solved. This was, what, 1981?, when engines still had carbs, floats, points. I went to the local Mr. Carb shop, and amazingly they had a used A-4 carb sitting on the back shelf. As I recall, the replacement carb had a foam float, so couldn't leak like the old one. (And if yours has a foam float, there goes my theory.) Good thing they had one in stock, he told me, or I'd be waiting weeks to order one. Can only imagine what the wait would be now. --paul
Paul,
When a float sinks, it opens the needle and lets the fuel in. Not shutting it off but turning it on. Like a toilet tank with a jammed float. The float is too low and the water keeps running. I'm a guy with a hotrodders gift. I can stand next to an engine and feel what's wrong or right with it. The biggest problem with an Atomic 4 is its stone-age design. That means everything is wrong with it. First it uses gasoline. Next it's a flathead. Next it uses gasoline. Next it has a 6:1 compression ratio. Next it uses gasoline. Next it's rated at 30 horsepower. And it uses gasoline. And it only has TWO main bearings. And it uses gasoline. And if run at a speed high enough to actually put-out 30 horse power the crankshaft will break. Oh hell, it'll break at any speed. And it uses gasoline. And it has less than half the range of a diesel. And it uses gaso,,,, P.S. OK JD. Here's the deal. Have the carb re-built. Send it over. I'll take care of it. BUT! YOU have to change the points and service the rest of the ignition system. Awful. And no guarantees. Wanna hear my 'three dead sets of new points in a row' story? Each set did the same as the last. Ran (or didn't run) just like yours.
When a float sinks, it opens the needle and lets the fuel in. Not shutting it off but turning it on. Like a toilet tank with a jammed float. The float is too low and the water keeps running. I'm a guy with a hotrodders gift. I can stand next to an engine and feel what's wrong or right with it. The biggest problem with an Atomic 4 is its stone-age design. That means everything is wrong with it. First it uses gasoline. Next it's a flathead. Next it uses gasoline. Next it has a 6:1 compression ratio. Next it uses gasoline. Next it's rated at 30 horsepower. And it uses gasoline. And it only has TWO main bearings. And it uses gasoline. And if run at a speed high enough to actually put-out 30 horse power the crankshaft will break. Oh hell, it'll break at any speed. And it uses gasoline. And it has less than half the range of a diesel. And it uses gaso,,,, P.S. OK JD. Here's the deal. Have the carb re-built. Send it over. I'll take care of it. BUT! YOU have to change the points and service the rest of the ignition system. Awful. And no guarantees. Wanna hear my 'three dead sets of new points in a row' story? Each set did the same as the last. Ran (or didn't run) just like yours.
Several possibilities ......
1. Crud in the carburator emulsion tube ..... just a speck of dirt will do it. 2. Blown head gasket (most likely/commonly between cycl 3&4.... 'with enough 'seal' to do a compression test but not enough 'seal' when one cylinder is drawing and the other is 'firing' under load. 3. restricted exhaust system 4. sticking exhaust valve. Since you just altered the fuel system, my bet would be the emulsion tube .... its the ~1" long brass tube inside the carb with 2 small holes bored in perpendicular to the axis of the tube. The emulsion tube is responsible for correct mixture when the engine is under load or at higher than idle rpm; that it idles but dies at load is indication of emulsion tube fouling.
1. Crud in the carburator emulsion tube ..... just a speck of dirt will do it. 2. Blown head gasket (most likely/commonly between cycl 3&4.... 'with enough 'seal' to do a compression test but not enough 'seal' when one cylinder is drawing and the other is 'firing' under load. 3. restricted exhaust system 4. sticking exhaust valve. Since you just altered the fuel system, my bet would be the emulsion tube .... its the ~1" long brass tube inside the carb with 2 small holes bored in perpendicular to the axis of the tube. The emulsion tube is responsible for correct mixture when the engine is under load or at higher than idle rpm; that it idles but dies at load is indication of emulsion tube fouling.
Fuel, Spark, Compression
The big three for gas engines. Check the air cleaner ignition system (pull the plug and make sure the spark is big and blue with a nice sharp crack) Compression (got that) Exhaust system for clogs ( my bet as to where the problem lies) fuel system (got that too) Don't forget to pray over the engine before you work on it, every 15 minutes during any work on it or while running it and thank God after you are done with the engine for not letting it break again.
The big three for gas engines. Check the air cleaner ignition system (pull the plug and make sure the spark is big and blue with a nice sharp crack) Compression (got that) Exhaust system for clogs ( my bet as to where the problem lies) fuel system (got that too) Don't forget to pray over the engine before you work on it, every 15 minutes during any work on it or while running it and thank God after you are done with the engine for not letting it break again.
yup, flooded
frank's right, and it's coming back to me now. yes, it was a flooding problem, not a gas shutoff. the result is what i said, tho: run's great just long enough to back out of the slip, and then that's it for the day. highlights the problem of having a gas engine, too, because then you're down there trying to get rid of some tablespoons of liquid gasoline. i think i must have suppressed that memory. gas as fuel is definitely the drawback with an Atomic. too bad, because it really ran pretty well, and was very easy to tinker with.
frank's right, and it's coming back to me now. yes, it was a flooding problem, not a gas shutoff. the result is what i said, tho: run's great just long enough to back out of the slip, and then that's it for the day. highlights the problem of having a gas engine, too, because then you're down there trying to get rid of some tablespoons of liquid gasoline. i think i must have suppressed that memory. gas as fuel is definitely the drawback with an Atomic. too bad, because it really ran pretty well, and was very easy to tinker with.
Stuck choke or gummed up carb.
but while you are at it replace plugs, points and condenser, check the connections from distributor and coil and test the spark plug wires for resistance. Adjust the valves, engine timing and check distributor spark advance. When installing the carburator make sure there are no vacum leaks. If you have good compression you should have a smooth running engine.
but while you are at it replace plugs, points and condenser, check the connections from distributor and coil and test the spark plug wires for resistance. Adjust the valves, engine timing and check distributor spark advance. When installing the carburator make sure there are no vacum leaks. If you have good compression you should have a smooth running engine.
Same problem Here!
Some great information here by some guys who have been in the same 'fix'. My A-4 has been doing the same as JD'S and I was looking to buy a carb, but sounds like the carb is easy enough to go through, and I'll find a kit. JD if you need a kit too, let me know, I'll send one on to ya. That back-pressure from the exhaust? Where do you dis conncet to flush it? Mine goes out of the steel 'chamber' located on the top port side of the engine, to a yoke with two large bolts. The yoke is connected to large black hose (reinforced with heavy wire) that is connected (with hose clamps) to a fiberglass elbow, then down to a large black 'mixer' mounted on plywood at the bottom of the port locker. From here it travels through another hose to exit out the port side. Thanks for all opinions, suggestions, critiques, or lewd comments.lol
Some great information here by some guys who have been in the same 'fix'. My A-4 has been doing the same as JD'S and I was looking to buy a carb, but sounds like the carb is easy enough to go through, and I'll find a kit. JD if you need a kit too, let me know, I'll send one on to ya. That back-pressure from the exhaust? Where do you dis conncet to flush it? Mine goes out of the steel 'chamber' located on the top port side of the engine, to a yoke with two large bolts. The yoke is connected to large black hose (reinforced with heavy wire) that is connected (with hose clamps) to a fiberglass elbow, then down to a large black 'mixer' mounted on plywood at the bottom of the port locker. From here it travels through another hose to exit out the port side. Thanks for all opinions, suggestions, critiques, or lewd comments.lol
Atomic Four
I've enjoyed the various comments on this thread for a very different reason. When I was 1st interested in sailing and didn't have a boat I was a guest of other owners. Sometimes there would be someone having an engine problem, typically with an Atomic Four and I offered to check it out. Even with my somewhat limited skill, I was often able to clean or re-build the carb and get the engine started, sometimes resulting in another invite for sailing. Bitten by the sailing bug, I eventually needed to buy my first boat. That was around 26-27 years ago --- thanks to Atomic Four engines!
I've enjoyed the various comments on this thread for a very different reason. When I was 1st interested in sailing and didn't have a boat I was a guest of other owners. Sometimes there would be someone having an engine problem, typically with an Atomic Four and I offered to check it out. Even with my somewhat limited skill, I was often able to clean or re-build the carb and get the engine started, sometimes resulting in another invite for sailing. Bitten by the sailing bug, I eventually needed to buy my first boat. That was around 26-27 years ago --- thanks to Atomic Four engines!
Easy to repair
I have a 35 year old Atomic four that runs like a champ. They are very simple to maintain and easy to work on. Did I say inexpensive to work on? Most owners are able to work on their own A4 but most guys with a diesel aren't. and repairing a diesel is a very exspensive hobby. Those are just some of the reasons that it is a GREAT engine IMHO. The engine is safe and reliable as long as the owner/user applies common sense and use safe practices. These engines have been around a very long time and although you always here of a few people that have had problems when you look at how many have been installed on boats the percentage is very low. ok...the problem is most likely a dirty carb..I say that assuming that you have checked your spark and it is good and the points are firing on time. The ecetric fuel pump comversion is pretty simple and it is hard to install wrong. You also said you were getting fuel to thru the filter so I am guessing you did it ok. these carbs are very simple so feel free to pull it apart to clean it. You can get rebuild parts from Moyer Marine http://www.moyermarine.com/ for $75.00 or you can buy a whole carb for $180. If you do buy a new one I would still order the gaskets and tinker with the old one. nothing else you learn what is in it and have a spare when you are done Get a can of carb cleaner to wash it all out with once it is pulled apart. There are very few pieces inside the carb abd it isn't hard to put back together. I have a few pages of how to's on it if you would like...how to set the carb and tune it when it is back on. let me know and I will email it to you. I do agree with RichH that it is most likely the emulsion tube. Pull it out and spray carb cleaner threw it. That should fix the problem. As for the ignition parts...I converted mine over to electronic ignition last summer and WOW! what a difference..I get better fuel consumption and much easier to start. Also not points to worry about. Again a very simple fix. Don't throw out the old points tho....leave them mounted on their plate and put in a box just in case you do ever have a problem you can drop them right back in. It doesn't make sense to change out a good engine on an old boat. I agree a diesel might be nice but they are very pricey. Putting a $7000.00 diesel on a $10000.00 boat doesn't make it worth $17000.00. If you had to scrap you engine then I would get a diesel...it would only make sense. But until then what you have will work just fine
I have a 35 year old Atomic four that runs like a champ. They are very simple to maintain and easy to work on. Did I say inexpensive to work on? Most owners are able to work on their own A4 but most guys with a diesel aren't. and repairing a diesel is a very exspensive hobby. Those are just some of the reasons that it is a GREAT engine IMHO. The engine is safe and reliable as long as the owner/user applies common sense and use safe practices. These engines have been around a very long time and although you always here of a few people that have had problems when you look at how many have been installed on boats the percentage is very low. ok...the problem is most likely a dirty carb..I say that assuming that you have checked your spark and it is good and the points are firing on time. The ecetric fuel pump comversion is pretty simple and it is hard to install wrong. You also said you were getting fuel to thru the filter so I am guessing you did it ok. these carbs are very simple so feel free to pull it apart to clean it. You can get rebuild parts from Moyer Marine http://www.moyermarine.com/ for $75.00 or you can buy a whole carb for $180. If you do buy a new one I would still order the gaskets and tinker with the old one. nothing else you learn what is in it and have a spare when you are done Get a can of carb cleaner to wash it all out with once it is pulled apart. There are very few pieces inside the carb abd it isn't hard to put back together. I have a few pages of how to's on it if you would like...how to set the carb and tune it when it is back on. let me know and I will email it to you. I do agree with RichH that it is most likely the emulsion tube. Pull it out and spray carb cleaner threw it. That should fix the problem. As for the ignition parts...I converted mine over to electronic ignition last summer and WOW! what a difference..I get better fuel consumption and much easier to start. Also not points to worry about. Again a very simple fix. Don't throw out the old points tho....leave them mounted on their plate and put in a box just in case you do ever have a problem you can drop them right back in. It doesn't make sense to change out a good engine on an old boat. I agree a diesel might be nice but they are very pricey. Putting a $7000.00 diesel on a $10000.00 boat doesn't make it worth $17000.00. If you had to scrap you engine then I would get a diesel...it would only make sense. But until then what you have will work just fine
William, wish I could agree.
But I can't. Like I said, stoneage design. So you think it's a dependable engine huh? Have you ever looked at the design of the rotating assembly? One small main bearing at the flywheel end of the crankshaft and another small bearing at the transmission end of the crankshaft. THAT'S IT! The entire center of the crank is unsupported. And it was sold as a boat engine! Boats don't go downhill. They are always under load. And if the factory realized that and built them with forged crankshafts (like all outboards) then that might help. But they didn't. Yep, cast iron (weak) crankshafts. They aren't just prone to breaking at the unsupported center. Mine broke at the flywheel end. Reasonably priced parts huh. Twenty one years ago the factory replacement cost of a A4 crankshaft was $1000.00. That's for crap that they didn't even magnaflux. (you know what that test does, right?) And ONE small main bearing, (the size of a cars' cam bearing) was TWICE AS MUCH as the entire bearing SET of a big block Chev. That cost, at that time, is still higher than a bearing SET for my 3GM30F Yanmar TODAY! Even in its day it wasn't a good design. That's not just my opinion. But I understand how men get attached to their equipment. I loved my A4. I would change the oil while it was still golden. Nothing was left to chance. Mine only received the best available care. But I loved it less after it wouldn't run with two different coils and three sets of points. (that was during vacation) Then when we were two hundred miles from home, in DESOLATION SOUND, the crank BROKE. (another vacation) No one sails those waters except for recreation. The tides are treacherous and the wind is often Nil. That was a survival sail to Friday Harbor. We didn't make it. The tide turned and the wind quit. That was the only tow of my life. Have you ever rebuilt an A4 on the dock? I have. Love is a two-way street. It won't last if it's not returned. Mine ended in Desolation Sound. Wanna talk about range under power? How about fuel safety?
But I can't. Like I said, stoneage design. So you think it's a dependable engine huh? Have you ever looked at the design of the rotating assembly? One small main bearing at the flywheel end of the crankshaft and another small bearing at the transmission end of the crankshaft. THAT'S IT! The entire center of the crank is unsupported. And it was sold as a boat engine! Boats don't go downhill. They are always under load. And if the factory realized that and built them with forged crankshafts (like all outboards) then that might help. But they didn't. Yep, cast iron (weak) crankshafts. They aren't just prone to breaking at the unsupported center. Mine broke at the flywheel end. Reasonably priced parts huh. Twenty one years ago the factory replacement cost of a A4 crankshaft was $1000.00. That's for crap that they didn't even magnaflux. (you know what that test does, right?) And ONE small main bearing, (the size of a cars' cam bearing) was TWICE AS MUCH as the entire bearing SET of a big block Chev. That cost, at that time, is still higher than a bearing SET for my 3GM30F Yanmar TODAY! Even in its day it wasn't a good design. That's not just my opinion. But I understand how men get attached to their equipment. I loved my A4. I would change the oil while it was still golden. Nothing was left to chance. Mine only received the best available care. But I loved it less after it wouldn't run with two different coils and three sets of points. (that was during vacation) Then when we were two hundred miles from home, in DESOLATION SOUND, the crank BROKE. (another vacation) No one sails those waters except for recreation. The tides are treacherous and the wind is often Nil. That was a survival sail to Friday Harbor. We didn't make it. The tide turned and the wind quit. That was the only tow of my life. Have you ever rebuilt an A4 on the dock? I have. Love is a two-way street. It won't last if it's not returned. Mine ended in Desolation Sound. Wanna talk about range under power? How about fuel safety?
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