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Go Back   SailNet Community > On Board > Gear & Maintenance
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  #1  
Old 10-24-2003
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agent4change is on a distinguished road
Atomic 4 is 4 lovers

Hey guys and girls! Capital, Newport 27; for all you out there. I have an atomic four that has a little problem, or I might not. When I throttle up out of gear I get all the RPM possible, but when I am in gear I only get thrust up to almost 2000 RPM and then after that point the throttle does nothing. Is this normal or do I have a problem, because I would like a little more power, huh? gracias for your input!
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Old 10-24-2003
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Atomic 4 is 4 lovers

Assuming your boat speed is less than reasonable at that RPM, it sounds like carb tune or ignition timing, or an incorrect prop. The carb and timing are easiest to deal with first. I printed the directions below, and made the adjustments myself successfully.

From:<<http://www3.bc.sympatico.ca/Atomic_4_Eng_Service/Frequently_Asked_Questions.htm>>

How do I adjust the ignition timing on an Atomic Four engine?




The ignition timing on an Atomic Four engine can be adjusted in several ways, but no matter which method is used, before the timing is adjusted the distributor should be serviced to make sure the distributor shaft bushings are lubricated with light oil (a few drops of oil on the little piece of felt under the rotor) and not worn beyond specification, the centrifugal ignition advance is properly lubricated and working smoothly, and the contact breaker (points) gap is adjusted to specification using a feeler gauge, or a dwell meter if one is available. Once this is done the engine can be timed.




Static timing can be carried out by turning the crankshaft so the piston for #1 cylinder is at the very top of its stroke (TDC) with both valves closed (firing #1 cylinder), the distributor rotor is pointing at the distributor terminal for #1 spark plug, and the distributor points are just beginning to separate. You can connect a battery powered light or buzzer across the points to determine exactly when they open. When #1 cylinder is at the top of its stroke the split pin in the front of the crankshaft will be pointing straight up and down.




Dynamic timing can be carried out by either tying the boat firmly to the dock or taking it out an area where it can be run at top speed for several minutes, connecting a tachometer to the engine, slightly loosening the distributor clamp screw, opening the throttle to get maximum engine speed, gradually rotating the distributor back and forth until the engine is running at the highest rpm possible, and then retightening the distributor clamp screw. At full speed the engine should reach at least 1,800 rpm (if it can''t, see "What size propeller should I use?" above).







How do I adjust the carburetor on an Atomic Four engine?




Early model Atomic Four engines were fitted with a cast iron Zenith 61 carburetor with 2 adjustment screws, one for the high speed main jet, and another one for the low speed idle jet. Atomic Four engines after 1968 were fitted with an aluminum alloy Zenith 68 carburetor with a fixed high speed main jet (some Zenith 68 carburetors have had adjustable main jets installed), but the same adjustable low speed idle jet as the Zenith 61. Assuming the flame arrester is not partially blocked by dirt and oil, and the carburetor is clean and in good condition with the float level set properly, the proper procedure is as follows:




Carburetors with fixed high speed main jets should have the main jet removed and checked to see what jet number it is. The jet number is stamped in very tiny numbers on the face of the jet. If it is not a #21 main jet, it should be replaced with one.




To adjust the idle mixture screw, initially adjust the idle mixture screw (the upper adjustable jet with the slot for a screwdriver) clockwise (in) until it bottoms lightly, and then out 1 turn. Connect a tach to the engine, start the engine, run the engine in gear until it is fully warmed up, then close the throttle, leave the engine in forward gear, and adjust the carburetor idle speed screw (the screw on the carburetor throttle arm that controls the throttle stop) until the engine is idling at 700 rpm, turn the idle mixture screw slowly out until the rpm drops noticeably, and then in again until the fastest idle speed is obtained. Readjust the idle stop screw to again set the idle speed at 700 rpm. Repeat the idle mixture adjustment again.




Carburetors with adjustable high speed main jets should be initially adjusted by turning the main jet adjusting screw (the lower adjustable jet with the little cross on the adjustment screw) clockwise (in) until it bottoms lightly, and counter-clockwise (out) 3 turns, and the idle mixture screw (the upper adjustable jet with the slot for a screwdriver) clockwise (in) until it bottoms lightly, and then out 1 turn. Connect a tach to the engine, start the engine, and with the boat running at top speed in forward gear (or tied to the dock) slowly turn the high speed mixture screw clockwise (in) until maximum rpm is obtained on the tachometer and then counter-clockwise (out) about 1/8 of a turn until the rpm just starts to drop.




Close the throttle, leave the engine in forward gear, and adjust the carburetor idle speed screw (the screw on the carburetor throttle arm that controls the throttle stop) until the engine is idling at 700 rpm, turn the idle mixture screw slowly out until the rpm drops noticeably, and then in again until the fastest idle speed is obtained. Readjust the idle stop screw to again set the idle speed at 700 rpm. Because the idle mixture setting has an effect on the main jet setting, repeat the main jet adjustment, and then the idle mixture adjustment 2 more times.




The rationale for setting the idle speed at 700 rpm in forward gear is to ensure the engine is idling fast enough to prevent stalling or erratic running when docking. An engine speed of 700 rpm in gear will also automatically increase to about 800 rpm when the transmission is shifted to neutral, which is high enough to allow the alternator to continue charging the battery.
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Old 10-24-2003
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Atomic 4 is 4 lovers

I believe it is proper to attribute the source when quoting, and it didn''t come through in the previous post. For the source, see:

http://www3.bc.sympatico.ca/Atomic_4_Eng_Service/Frequently_Asked_Questions.htm
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Old 10-26-2003
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Atomic 4 is 4 lovers

thanks for your help. that is an excelent web site. I also emailed Don Moyer at Moyer Marine and he said that sounds normal for the RPM, Anyone out there with a 1974 Capital Newport 27'' with an atomic 4 engine. I just wanted to compare and see similarities; and maybe improvements.
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Old 02-21-2004
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Atomic 4 is 4 lovers

A4 is in 77 Newport 30. Knocking suggests cam and rod bearings. Runs well but scary. Need mechanic in Deale, MD area. Diagnose and/or repair.
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Old 03-30-2004
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Atomic 4 is 4 lovers

I have an Atomic 4 1979 in a Catalina 38 I also have a power prop that gives it a bit more thrust in reverse since Cat38 boats dont back down for nobody. The motor will inly make 2000 rpm at full power. I find it pushes the hull at 6.5 kts at 1500 rpm and gets a fair fuel burn and don''t shake rattle or roll. I was talking to a guy who was getting me some parts and he said the Atomic crank was near $4000 bucks for our friend with the knock fix it fix it now. The reason for the high price is for a couple of grand more you have a new motor marketing people suck. I am switching lube in the motor to full synthetic AMSOIL which I sell flushing the motor and getting rid of all that carbon.Longer oil change periods and engines run cooler.
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Old 03-31-2004
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Atomic 4 is 4 lovers

4k for a new crank. I have seen many rebuilt A4s for less than that.
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Old 04-01-2004
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angiewilson is on a distinguished road
Atomic 4 is 4 lovers

For the guy with the knock try some Marvelous Mystery Oil in the fuel mix. Add 6-8 oz to 10 gal of fuel, but first just put some right into the spark plug holes.... you will be amazed!

For the guy who was quoted the 4K for the crank.... I''ve got some ocean front property in TN that I can make you a great deal on....You can get a completely upgraded/rebuilt A4 thru Moyers Marine (the guru of the A4) for about $2700.
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Old 04-01-2004
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Atomic 4 is 4 lovers

For the guy wanting a little more thrust... your prop gets to spinning so fast that it is not really pushing water anymore but acting more like a food processor. If you have checked the timing and carb adjustment you may want to think about adding a fence to your prop blades so they have a little more thrust at lower RPM
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Old 08-07-2011
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Web Site

Quote:
Originally Posted by dpboatnut View Post
I believe it is proper to attribute the source when quoting, and it didn''t come through in the previous post. For the source, see:

http://www3.bc.sympatico.ca/Atomic_4..._Questions.htm

Cannot connect to this site. Possibly down. Please check and resend

TIA

Bill
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