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]

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]

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]

exhaust?

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]

Pt II

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]

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. . .