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Old 05-27-2019, 05:10 PM
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Atomic 4 Timing Resources...and a question about surging

I wanted to say thank you and try to give back by consolidating some of the amazing resources on here that I used to successfully time my Atomic 4. I'm hoping that this helps future users by trying to put a lot of info in the same place.

Like others, my engine was significantly advanced and I had a lot of blowby that I was hoping to correct. The engine idled at very high RPM (I don't have a working tach - yet) and there was a lack of power at the top end. My results after the timing process was complete: idling well at about 1000 rpm. Testing out on the water this weekend I had almost a full knot higher boat speed - amazing! I highly recommend taking on this project, you will be amazed at the results. OK, on to the process.

First, here are the previous posts I found most useful. In case the forum server crashes or changes, I've also put the post title, poster, and date. This helps to retrieve it from Google which seems to be more efficient at finding posts than the forum search feature
Timing Under Power and Idle by WrongWay 08-11-2017
http://www.moyermarineforum.com/foru...ad.php?t=10351
Timing Pointer by ndutton 12-03-2010
http://www.moyermarineforum.com/foru...ead.php?t=4743
A Pump Pictorial by ndutton 12-04-2010
http://www.moyermarineforum.com/foru...ead.php?t=4746
Idle Speed Adjustment by cemory 08-16-2012
http://www.moyermarineforum.com/foru...ead.php?t=6691

What I did:

I installed thatch's timing pointer (as described in the post above) on the accessory drive which was so much more accurate than the roll pin. To achieve initial timing, and find Top Dead Centre, I used Don's tech video.


Next, I marked TDC on the pulley with white paint, as well as painting the top of the roll pin. Finally, I lined up thatch's timing pointer with the mark and started the engine. I bought a digital timing light with advance for the process - so worth it! It immediately showed the timing was significantly advanced so I loosened the distributor hold-down bracket and rotated the distributor clockwise until the mark was lined up. RPM's went down, but not to 1000, so I had to adjust the idle speed screw counter-clockwise. As I did this, I realized the idle jet adjustment was too lean and had to make it richer by turning it all the way in and then back out half a turn. That worked. Below is a video of the completed process:

[YOUTUBE]ZGXD_jTFtQU[/YOUTUBE]

Now, all of those posts contain a treasure trove of info, but they're also really long. I'm going to try and post the info I found most helpful in quotes here. (Hopefully the photos come along with the comments). Alright, hope this works and is useful for someone else. (Or me next season

Quote:
Originally Posted by ndutton View Post
Check out Thatch's innovative timing mark system. On his Catalina 30 there is no access to the flywheel without cutting a hole in the dinette seat bulkhead so he took advantage of the 1:1 ratio between the auxiliary drive and crankshaft. This would work well for the V drive guys too. He has two painted marks on the drive pulley: one at TDC and the other at the proper advanced angle.

Nicely done.
Quote:
Originally Posted by thatch View Post
Rigs,
On a Catalina 30 the flywheel end of the engine is covered by a non-removable piece of cabinetry. The solution to setting the timing on the A4 has been to either "power" tune by feel or to cut an access hole to be able to see the crankshaft pin. Since the accessory drive is a gear driven 1:1 unit it seemed to be the right place to add timing marks and a pointer. After doing a little math I painted 2 dots on the pulley lip .559" apart which represent TDC and 17 degrees of mechanical advance. Being right next to the distributor makes timing checking a snap, at least on a Cat 30.
Tom
Quote:
Originally Posted by thatch View Post
Hi Shawn,
The .559" figure should actually read .556", sorry. This represents 17degrees of a 3-3/4" circle which is the O.D. of my accessory drive pulley. After you have fabricated the pointer out of SS clamps there are 2 ways you can go. If you like the way your A4 is currently running, by trial and error using a timing light and some small pieces of tape find where the "at idle" timing mark should be. Then using the same method run the engine up to about 2000 RPM and establish the advance mark. It should be about 9/16" in the advance direction from the idle mark. You can then use white fingernail polish to make the marks more permanent. The other method which will establish an actual TDC mark is to set the flywheel crank pin on the compression stroke at 0 degrees and then put a white dot on the pulley and align the pointer to it. I have given both methods because it seems that most A4's are adjusted at something other than TDC at Idle. These marks are really intended to make it possible to return your timing to a "base line" setting and to check the condition of the centrifical advance mechanism.
Hope this helps, Tom
Quote:
Originally Posted by ndutton View Post
I was in the middle of looking to improve power when Tom mentioned his timing thoughts and concerns to me back channel. I had recently purchased a 10 x 8 two blade prop on ebay to replace my stock 12 x 7 two blade. After installing the new prop I was disappointed in the RPM improvement. It was better but didn't come close to my expectations. With the 12 x 7 I maxed out at 2100 RPM, the new 10 x 8 gave me a measly 200 RPM increase, now 2300. Simple math showed a 9.5% improvement from the prop change alone.

It was when I was whining to Tom about the amount I'd spent (prop + professional diver installation) for a disappointing result that he started talking about timing. Well, I was confident my timing was good, the engine ran well and has always started easily and (haruumpf haruumpf) I was experienced in the timing by feel method prescribed by Universal. Tom tactfully suggested maybe we should actually measure how accurate my timing was. Sounded like a good idea to me.

Tom gave me a homework assignment prior to him driving in for precision measurements. Because I have a Catalina 30 with the end of the crankshaft covered by interior structure (where Universal's only timing mark is located) I was to make my own readily visible timing mark as accurately as I possibly could using the accessory drive pointer I'd made for my spare engine under Tom's tutelage a while back.

I cut an access hole in the dinette seat riser to see the crankshaft roll pin, opened the distributor cap so the rotor would give a rough indication of when I was approaching #1 TDC as I turned the engine by hand. Once I was close I shined a flashlight on the roll pin and aligned it with the hand crank as vertical and on the flywheel cover notch as I could. Once there I marked the accessory drive pulley with white paint, then installed the Thatch timing pointer in careful alignment with the mark. That done, it was time to bring out the timing light.

I checked the timing at idle (no advance weight deployment) and whoa Nelly, my timing was alarmingly advanced, like an estimated 10°. Well, that was a sobering moment, maybe I'm not as adept at timing by feel as I thought. I loosened the distributor hold down clamp and rotated until I was on the mark, 0° BTDC. As the timing was adjusted the idle RPM dropped 100 RPM too. Time for a test run.

Whoa Nelly again, now I can reach 2600 RPM (a 13% improvement due to proper timing alone). Yeah guys, 2600 RPM for a direct drive A-4! Man, that's a reduction gear number. As always, YMMV. The significant improvement I experienced speaks in a large part to how off my timing was to start with but in my defense, I had previously followed [one of] Universal's published timing instructions carefully.

When Tom drove in with his precision TDC measuring equipment a week later we found that I'd been able to make a very accurate mark using the roll pin carefully. I've attached pictures of the new timing mark and Tom's dial indicator apparatus.

I'm looking forward to what so far looks like additional improvements with his advance spring testing. So far for me, prop change + timing precision has resulted in an overall 23.8% increase in max RPM.
Quote:
Originally Posted by romantic comedy View Post
Is there an agreement as to the timing settings?
Quote:
Originally Posted by ndutton View Post
The specs I have (Robert Hess) are 0 degrees BTDC at idle and 17 degrees BTDC at 1800 RPM.
Quote:
Originally Posted by JOHN COOKSON View Post
Well, I went down to the boat today. Marking the accessory drive pulley won't work for me because of poor\no access.
I went for "Plan B" and marked the roll pin and hooked up the timing light. With the engine warmed up at idle the mark was 1 to 2 degrees to the right of the timing mark in the flywheel cover. This means the timing is very slightly retarded?
It's been going round and round in my head which way to turn the distributor to bring the timing to TDC. Can't figure out. Help.
Rotating the distributor a micro smidgen in the correct direction should bring the timing to TDC. There is no way I can read the timing light and rotate the distributor at the same time like I would like to do.
Then again maybe I should just leave it alone?

TRUE GRIT
Quote:
Originally Posted by ndutton View Post
Your timing light indicates you're slightly advanced so you'll need to rotate the distributor body clockwise to correct. You also might consider Tom's window in the flywheel cover to establish a mark on the flywheel perimeter. I don't have the dimensions right now but I estimate it will provide about 8x more accuracy than the roll pin.
Quote:
Originally Posted by cemory View Post
All,

Engine runs great but when I attempt to lower the RPMS to a minimum the engine cuts off. This is a Edson pedestal system. Is there an idle speed screw on the carb or do i need to adjust the cable.

Thanks,

Coy
Quote:
Originally Posted by roadnsky View Post
Coy-
Welcome to the forum.
Yes, There is a throttle adjustment and an IDLE MIXTURE screw on the carb.
(See drawing and pic)

You turn the IDLE MIXTURE screw in (clockwise) to make the mixture richer, and out (counterclockwise) to make it leaner.

When engines stall while idling, it is usually because they are too lean. This means that you may want to turn the mixture adjustment IN a half turn or so as your first shot. If the engine idles worse, turn the adjustment back out until it idles reliably.

When was the last time the carb was cleaned? Do you have filters upstream of the carb?

There are volumes of threads here on the site about the carb and adjusting, cleaning it.
The onsite catalog also has video you can download that is very educational.

http://www.moyermarine.com/cgi-bin/s...rebuilder.html
Quote:
Originally Posted by sastanley View Post
Coy,

In addition to the nice pics & diagram Jerry provided, if you follow the throttle cable to the carb, you'll see a small stop screw at the base of the armeture that adjusts idle speed. Screwing it in moves the arm towards the back of the boat, and raises the minimum idle speed a bit. Do you have a tach so we know when it is dying out?

Mine seems to like 800 or so RPM for idling, but with a real clean and properly adjusted carb, they can reliably idle at 5-600 RPM.
Quote:
Originally Posted by roadnsky View Post
Some more pics of what Shawn is describing...
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  #2   IP: 174.93.49.251
Old 05-27-2019, 08:18 PM
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Bummer, I was hoping all those great pics would be in there too.

Anyway, here is the question part about the surging. Not sure what's causing it or the solution. I edited the video down so you can see there's one about 40 secs in and then again at about 1:35 when I'm not touching the throttle or the idle speed screw at all.

[YOUTUBE]OmFUwCll-xw[/YOUTUBE]

Let me know what you think...
thanks,
Trevor
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