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  #1   IP: 66.193.187.114
Old 09-03-2019, 12:31 PM
DCHunt DCHunt is offline
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Engine runs but has low power

We have a late model Atomic 4 in a Pearson 36 sailboat, built in 1972. We have only used it in fresh water (Lake Erie) and have maintained it over the years with parts from Moyer. About 5 years ago, we replaced the head gasket, cylinder head and exhaust manifold because of a crack in the cylinder head. It has run fine since until about 1/2 way through the summer when my brother was running it at speed and he heard a couple loud pops. After that, it will run but has low power.

I have replaced the spark plugs. The first two closest to the flywheel appear to have more carbon on them than they should. I checked compression and it is 75 to 80 psi in all four cylinders. A guy that knows a heck of a lot more about engines than me took a look at it and found that when it was running and he opened the throttle, it took 3 or 4 seconds or more for the engine to rev up. He thinks it may be a carburetor issue. We replaced the carburetor about 10 years ago.

What other things should/could I look at that would cause this low performance? I'm ready to order a new carburetor from Moyer but wanted to check to make sure there wasn't something else I was missing.

Thanks,

Dan
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  #2   IP: 67.176.201.200
Old 09-03-2019, 03:44 PM
Sam Sam is offline
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Well, I would hold off on ordering a new carb - maybe a rebuild kit. The loud pops and low revs sounds like a possible timing issue. I 'd pull the distributor cap and check if the rotor "snaps" back after manually rotating it bit...checking the advance springs. I would also check for spark in all cylinders, 1-2-4-3 plug wiring sequence, condition of or change cap and rotor.
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  #3   IP: 216.80.24.55
Old 09-04-2019, 12:32 PM
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Antibes Antibes is offline
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3-4 seconds to rev up definitely sounds like the advance springs are the place to start
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Old 09-05-2019, 11:38 AM
DCHunt DCHunt is offline
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Thanks Sam and Antibes. My mechanic friend played with the weights or something in the distributor and he thought they were free?? Is that what you are talking about? A while ago I put in a Perfronix Ignitor Ignition and an Ametek coil. Not sure if that is useful or not.

Sam, where are the advance springs?

A new carburetor from Moyer will be here tomorrow. I'll see if that fixes it.

Also, Moyer calls for RJ-12C spark plugs. I can't seem to find those at NAPA. What are good spark plugs to use as a replacement?

Thanks,

Dan
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  #5   IP: 216.80.24.55
Old 09-05-2019, 12:45 PM
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The weights in the distributor are connected to the advance springs. They should be oiled as part of regular maintenance. If they move freely that would rule them out
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Old 09-05-2019, 01:07 PM
Sam Sam is offline
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Advance springs are under the distributor plate w/weights etc. sounds like your mechanic checked them. I'd still rotate the rotor now and see if it still has some "snap back"? I don't have an alternative plug since I use the same Champion RJ12 plug. Used to use the std recommended and common J8C in early years without any dramatic designable differences.

I hope the carb replacement works for you but I think you'll find the expert folks on this site and past threads generally advocate for more of a diagnostic approach - vac pressure, fuel pressure, spark color , coil readings, voltages etc etc. rather than opting to changing out expensive components [except for cap/rotor/wires] I say this because I still use my original zenith carb from 1966 on a good running A4. Still, experience can sometimes quickly point to the problem. good luck.
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  #7   IP: 207.118.20.35
Old 09-05-2019, 06:30 PM
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capnward capnward is offline
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This sounds like a timing problem, which a new carburetor will not affect. Sounds like your advance weights are lubricated enough. Cap and rotor are easy to replace. Did you try turning the distributor clockwise to retard the timing? I believe this has the effect of richening the mixture. Do this as it is running at speed under load, and listen for the change in sound. RPMs will change as you do this. If it sounds more throaty you will probably have better power. If you have a vacuum gauge and it goes up, the engine is working less hard, and can generate more power. I think loud pops are a symptom of the mixture being too lean. Other ways to richen the mixture are to turn in the idle screw, or to turn out the adjustable main jet, if you have one. I had loud pops like backfiring when shutting down, and it went away when I turned the distributor clockwise a bit.
If your problem is crud in the fuel and jets in the carburetor are partially blocked, the new carburetor will develop the same problem. You will need to disassemble the carb and remove and inspect the tiny idle jet, in particular, for blockage. File down a small screwdriver to fit perfectly in the jet without damaging the threads around it.You can remove the crud from the jet by running a wire from a wire brush around in it, and reinspect. Also run a wire in the idle ports. Take care not to bend the float bracket. Rotate the wooden dowel that comes with the carb rebuild kit to dress the seat of the float valve. Reassemble with new gaskets. Replace the inline fuel filters at the same time. Here is the diagram of the carb.
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  #8   IP: 70.185.132.167
Old 09-05-2019, 07:31 PM
JOHN COOKSON JOHN COOKSON is online now
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The prop may be fouled. The "loud pops" you heard may be the KRAP hitting the hull as it wrapped around the prop.

TRUE GRIT
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Old 09-09-2019, 12:57 PM
DCHunt DCHunt is offline
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Thanks, guys, for the help. I did replace the carburetor and that seems to have fixed the poor performance. I did change the main fuel filter and a Moyer polishing filter this year on the engine but replacing the carb seems to have done the trick.

I still think that the timing isn't right. My problem is trying to reach in to turn the distributor while the engine is running. There is not a lot of room to do this. I'll see if I can figure something out on that approach.

Thanks,

Dan
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Old 09-09-2019, 06:08 PM
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capnward capnward is offline
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If a new carburetor did the trick, your old carb had issues that can still be resolved for much less money than a new carb. Then you will have a working spare, which is nice, because your new carb may develop the same issues. Plus you will have gained experience working on your carb. Over time, A4 owners become skilled at carb cleaning and distributor turning.
The hard part of distributor turning is reaching in with a 1/2" wrench to turn the hold-down bolt with one hand, while bracing yourself with the other hand at a spot separate from the engine. You might practice that without it running first. Don't loosen it too much, just enough so that the distributor will stay in the position that makes higher rpm, or lower vacuum. Then tighten it. Good Luck!
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  #11   IP: 70.185.132.167
Old 09-09-2019, 11:56 PM
JOHN COOKSON JOHN COOKSON is online now
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Stand By - There May Be A Second Chapter.....

Quote:
Originally Posted by DCHunt View Post
Thanks, guys, for the help. I did replace the carburetor and that seems to have fixed the poor performance.
Dan
Changing out the carb may have fixed the poor engine performance but did it fix reason the carburetor didn't work well? Doubtful. Time will tell. At a minimum catch some fuel in a clear glass jar and hold it to the light to see if there is any crud in it.

BTW: You need to service the advance before you fiddle with the timing. Especially if you haven't serviced the advance in the last year or 50 engine hours. Twisting the rotor to see if the springs snap it back is not good test because the weights need to be free to move with as little friction as possible for the advance to work properly.

TRUE GRIT
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