intermittent misfire, new issue with rebuild

[Cool Beans]

Never ending. . .I'm going to change my name to "Can't Win for Losing"

SO! If you look back at my previous videos, the engine seemed to run fine with no misfires. . .the misfiring started after I clocked the distributor. I've set and reset the timing, and did a third time today when my dad came over to listen to it. Pulled plugs, TDC #1, rotor pointing to #1. I want to say it is coincidental. Plus, it's so random. . .if it was out of time it would be a regular miss (if it even started).

He was also there when I cold started it. While cold, and for the first few minutes it ran great. . .he of course made me feel like I was crazy, lol. But it started to miss worse as it warmed up. I will post a video shortly of it running while hot. I installed new plugs. I cleaned up the contacts on the cap and rotor. Wires look good, didn't find any carbon tracking in the cap.

I cracked the carb open and it was clean as a whistle. I drained the sediment bowl and it was clean as well. I haven't blown the polishing filter out yet. . .in the video, you can see me turning the idle screw from rich to lean and it seems to make the misfire worse on either side or normal? Normal setting still misfiring, though not as bad. My dad thinks it might be fuel related, but why would it run great for a few minutes cold? I'd think it would take awhile for the carb to get hot enough to do anything. . .

Plugs look like they have a film of oil (see pic)? But, the center portion is dry (I've had worse/wetter plugs in my truck before I rebuilt the 460 and it ran great). And I'm noticing smoke when gunning it that might be oil? So much for rebuilding, lol. . .does it need to be run under load for a couple hours to seat the rings? I know you do that with an car/truck motor. Is excessive idling in the driveway screwing it up while I try and get it to run right?

I appreciate all the help in figuring my project out. It's hard to think clearly on my own when I've mostly spent the last week fantasizing about burning the boat down to the waterline and smashing the motor with a sledge

EDIT: Video is here https://www.youtube.com/watch?v=LwyA...ature=youtu.be

Audio sucks, you really have to turn the volume up and listen for the misfiring. It's sounds like crap in person.

[hanleyclifford]

I've heard worse. Couple of questions: have you checked your dwell with a meter? Have you timed the engine with a strobe and if so what is your total advance?

[Cool Beans]

I've heard worse too. . .but I'm an overly worried, compulsive worry wart who can't leave well enough alone

I have not checked for total advance, and I have EI so I can't adjust dwell, can I?

Here's something. . .I was able to unscrew the idle screw from the carb body? It still ran, and not much if any worse than now

[hanleyclifford]

Originally Posted by Cool Beans

I've heard worse too. . .but I'm an overly worried, compulsive worry wart who can't leave well enough alone

I have not checked for total advance, and I have EI so I can't adjust dwell, can I?

Here's something. . .I was able to unscrew the idle screw from the carb body? It still ran, and not much if any worse than now

Good that you have EI - one variable eliminated. Timing should be set with a strobe at around 1500 rpm for a total 34 degrees. You will be able to see if the strobe is steady. Advance should come from TDC to full advance smoothly as rpm increases. This is a good test of your advance springs and weights. In tune up the carb is the last thing to be adjusted. BTW, if an engine runs nice until it warms, and then starts skipping, be suspicious of valve lash settings.

[Cool Beans]

Originally Posted by hanleyclifford

TW, if an engine runs nice until it warms, and then starts skipping, be suspicious of valve lash settings.

Interesting! I'd never set solid lifter lash before this rebuild. Initial lash was set cold, back in February?

[Marty Levenson]

You might try removing the exhaust. Any restriction there could be the problem, and its easy to check.

I feel your pain!

[Dave Neptune]

Beans, first since it idled about the same with the idle screw out I suspect float level being to "hi" making to overall carb rich. As this screw adjust air it can still run~~sorta.

Second take a look at the order of the plug wires even if you have done so already. May even back the timing "back a few" degrees.

If no joy on the above look at the valve clearances. If you are to tight the valves may close when cold but be open slightly when warmed up.

By the look of the plug my first "guess" is to the carb and possibly an influence of timing.

Note, did not listen to the vid yet.

Dave Neptune

[Dave Neptune]

Beans, yes there will be a good deal of oil getting by the new rings until they seat ~normal~. Theycan take a long time to seal in a hi-nickel bore if not perfect from the shop and even then more than a few hours.

Don't worry about the oil yet!!!

Dave Neptune

[JOHN COOKSON]

Sounds 2 me like a weak spark plug or spark plug wire shorting out or maybe a broken valve spring or a valve lash setting not right. All these parts are new so ??????????
When it starts missing pull a wire off a spark put a screw driver in the boot and see if you can jump an arc to the plug.
Best I can do for now.

TRUE GRIT

[Tim]

My rebuild is at about the same point as yours and I had the same problem. Today I adjusted the valve clearance and that seemed to help. Then I adjusted the point gap, that has fixed the problem for now.

[Tim]

After further testing, I am able to re create the misfiring by turning the adjustable main jet.

[JOHN COOKSON]

Originally Posted by Tim

Then I adjusted the point gap, that has fixed the problem for now.

Tim
After you reset the point gap what was the dwell reading? You may have a distributor problem such as a worn cam. The dwell reading should be the same at all engine RPMs.
If the point gap and dwell are both in spec you probably do not have a distributor problem.

TRUE GRIT

[Tim]

I have no idea what the dwell reading is. I have an A4 in my boat, and I have another A4 in my garage that I am finishing the rebuild on. The A4 on the boat has EI, the one in the garage has points. When the rebuild is complete the motors and distributors will be swapped. I am just trying to get the rebuilt engine tuned as well as possible prior to making the engine swap.

[Cool Beans]

Going to HOPEFULLY have a chance to mess with this today or tomorrow. Friday/saturday was all my brothers wedding stuff. . .today is a cook out. . .tomorrow is my other brothers birthday, lol. . .

Maybe, just MAYBE. . .I might have a few minutes to adjust the valves again

If nothing else, it is a nice long weekend

[Cool Beans]

#%@$!

I was hoping the valve adjustment would be a smoking gun. . .one exhaust valve was a little tight, but nothing I would be shocked at. All the other feelers slide in and out ez.

Ran the engine. Barely audible, random mis at start up. . .getting louder and more frequent when hot. The randomness is killing me! If it was consistent, I think it would be easier to figure out. . .

You can put your hand on the exhaust and feel the pops.

Going to try and track down some local, acceptable ignition parts and clean out the carb. I think I have an old coil at the boat I might swap for craps and giggles.

Is there anyway to test the ignitor?

Interesting note: While advancing and retarding the distributor, the idle would get worse and the random misfire was still there. . .

[hanleyclifford]

I know it's late in the day, but have you eliminated bad cap and/or rotor from the investigation? Look for raised track inside the cap from one of the terminals.

[Cool Beans]

No raised tracks. I sprayed the inside with carb cleaner just to be sure there wasn't any residue anywhere. None of the wires have corroded ends, and none of them get hot so I'd guess they are not high resistance? When you pull the plugs off running, you can hear the "snap" of the spark jumping from the top of the plug to the inside of the boot.

I cleaned out the carb. It was spotless everywhere before and after, and the float is parallel with the carb body per the manual. I also eliminated the polishing filter because why not, lol.

I'm going to setup some timing marks and throw a light on it.

I'm almost ready to just buy and exchange engine like I should have done 5 months ago. . .it would suck to have eat the money spent so far

[hanleyclifford]

Originally Posted by Cool Beans

No raised tracks. I sprayed the inside with carb cleaner just to be sure there wasn't any residue anywhere. None of the wires have corroded ends, and none of them get hot so I'd guess they are not high resistance? When you pull the plugs off running, you can hear the "snap" of the spark jumping from the top of the plug to the inside of the boot.

I cleaned out the carb. It was spotless everywhere before and after, and the float is parallel with the carb body per the manual. I also eliminated the polishing filter because why not, lol.

I'm going to setup some timing marks and throw a light on it.

Good. The light will do two things. First, it will allow you to set initial at factory spec - TDC. Second, it will allow you to observe as centrifugal advance mechanism smoothly advances timing to full factory spec. It will also reveal any problems with the springs or weights. Even though you have EI it wouldn't hurt to put the dwell meter on and watch it as the engine skips...

[Tim]

My rebuild was still misfiring randomly, so I searched the forum for some wisdom. I came across this from Don Moyer:

"If you have a late model engine, be sure to install the fly weights so that you can rotate the rotor a slight bit in a clockwise direction (it will return by spring tension). If you can rotate the rotor only in a counterclockwise direction, you installed the fly weights upside down."

I had taken my distributer apart many moons ago and to clean and refurbish. Sure enough, I put advance the weight assembly together backwards. I reassembled it correctly today and the misfires are gone.

[JOHN COOKSON]

CB
This is kind of far out there but anyway........
Check to see if a spark plug wire is shorting out. Running the engine at night is the best way to see this. The wires need to be in their normal working position ie laying on the head. If you lift the wire off the head as you did when you checked for spark it may be far enough away from the head so they don't short out.

TRUE GRIT

[Cool Beans]

Just checked, I can rotate a couple degrees clockwise. Glad you said something though, because I just put it together thinking it only went one way

Factory spec is TDC? I always timed it to the highest, smoothest RPM possible Going to set to TDC and see. Video is coming shortly of my hand timing that I just did. Interesting to watch the timing hunt as rpm's increase

[Cool Beans]

TG, I will try a night run if I think the neighbors won't call the cops on me

SO. . .reducing the timing to TDC greatly reduces the intermittent miss. It's still there, but nearly inaudible. It gets to be noticeable when the throttle is increased, but not nearly as bad as it was. Still there, but at least I wouldn't be worried about blowing the rubber exhaust hose apart. I feel a bit better. . .I keep forgetting I'm not building a truck motor

Here is the video of it running before I retarded the timing. When the rpm is increased, note how the timing seems to hunt around? Never seen the before with any vehicle I've had. . .but they were all vacuum advance or Ford electronic TFI.

https://youtu.be/Zf-xrwIQ95E

[hanleyclifford]

Doesn't look like you are getting 34 crankshaft degrees with that centrifugal mechanism. Use a protractor to mark 34 degrees and see if you get there from TDC.

[JOHN COOKSON]

Originally Posted by hanleyclifford

Doesn't look like you are getting 34 crankshaft degrees with that centrifugal mechanism. Use a protractor to mark 34 degrees and see if you get there from TDC.

I measured the angle to be ~ 12 degrees with a cheap plastic protractor on my computer screen.

CB: Are you sure the advance mechanism is right?

TRUE GRIT

[Cool Beans]

You guys are giving me more clues to punch into the Google. . .

34* sounds like the total advance for my 289! Unless that is for WOT, which I'm afraid to try in neutral sitting on the stand. I don't know if that is WOT in the video, that's just as much throttle as my ears can stand, lol. Might be close, might not be?

As far as I can tell, it is rebuilt correctly. No rust, lightly oiled, weights move freely. The return springs are a little rusty, might be worth replacing? I can post a quick video if anyone is interested.

I did find this interesting post via Google Images by accident, trying to find pictures of the advance mechanism:

http://www.moyermarine.com/forums/showthread.php?t=2324

In 1995 we published an ignition advance curve in one of our Atomic 4 Newsletters (copy attached). This curve (developed by Tom Stevens of Indigo
Electronics) shows that the ignition advance continued to 21 degrees at 2000 RPM.

Of more relevance is the question of why your engine doesn't like the higher advance at high RPM. My guess is that you're evaluating your performance in neutral. For some reason (that I've never figured out) the Atomic 4 develops a slight "hiccup" at higher RPM in neutral. This anomaly is not present while the engine is under load. As long as your engine pulls smoothly under load up to its maximum RPM available, you should be OK.