Diagnose these fouled plugs

[Groover]

It ran only slightly better when we first started (at that point it was static timed), but it's never really been right.

We didn't rev it much then nor did it get to fully warm up because it was in the garage. It ran about 10 minutes total in 5 or 6 different efforts (we had the starer issue so it couldn't run much until we got that fixed).

It never backfires or pops back through the carb. When we rev it quickly, it sounds like it's sucking a bunch of wind and it nearly dies if you don't let off. If we rev it gradually, it will get up to 2500 RPM, but that's about as far as I've taken it.

With the vacuum off the distributor and plugged, it will idle pretty well around 825 RPM (when I put the vacuum back on it starts to develop that little stutter). And we can put it in drive and it will drop to about 650 and still be pretty good, it'll even drive forward, but once you get it under load (like a parking bump or the edge of the garage -- as in the video -- it stalls out unless you have running start).

Is there a chance that the lifters are all pumped up and the valves are staying open (maybe 2 & 5 more than the others) but all a little open? Idles fine, but loss of compression when it's under load?

Thinking get it fully warmed again, and run them just a hair tighter than clattering instead of the full 1/4 turn?

[Groover]

So I don't think this is completely related, but what does it mean that this little port (the one at the bottom that is supposed to be sucking air from the choke tube off the exhaust manifold) is open and has pretty good vacuum even when we're fully warmed up?



Seems that once it's warmed up, this wouldn't continue to suck warm air up from the manifold or is that continuous (and necessary) in which case, it's sucking air but not as hot as it could be?

I know the one at the top is supposed to suck from the air cleaner. This carb is from 65.

[poboyjo65]

I think that just helps turn the choke open quicker . have you tried timing it by ear? then try to drive it. play around with it to see if you can get it not to stumble on take off. you can always put it back.

[popscomet]

with the motor at full temp,with out the air cleaner on the carb and at normal ideling,take your hands cupped together and put them over the carb,as tight as you can try to choke it til it dies,if you can't choke it down or dead,,you have a vacumn leak,if you can ,no leak,thats some more of that back yard stuff......

[jpet]

If you have any suspicion of a vacuum leak, spray starting fluid in the suspicious area. If your motor revs up, there is a leak.

[B_Hix]

Just a little .02......^^ following up on Pops simple test, with the car running, at normal temp disconnect a hose hooked to manifold vacumn. If the car speeds up your too rich, if it tries to die or does die you are too lean. That'll help get that carb dialed in good enough to move on.

Do not discount the possibility of bad plugs. We have all seen a plug that once fouled never works right again, even cleaned up - can give a fella fits. At $2.00 a shot can't hurt, and keep in mind most are coming from places the workers get .30 cents an hour...

GAP - what gap are you running? for a 260, as I recall I ran a .35....? been a while tho. That was with an accell dizzy.

Cap and rotor - what condition are they in? Look at the contacts on the cap for those rich cylinders - consistent wear pattern?
Stating the obvious, but the plug wires could be suspect too- give her the start at night test and see if them wires are shorting out on anything.

Like someone else said, if the valves are too tight they might not be closing all the way. Back'em off till they tap then give 1/4 turn or so.

Timing - if it's bad outta wack could be firing at the wrong time, making those two cylinders look troubled.

[Groover]

Cap and rotor - what condition are they in? Look at the contacts on the cap for those rich cylinders. Stating the obvious, but the wires could be suspect - give her the start at night test and see if them wires are shorting out on anything.

Been doing some thinking on this.

Last night when I pulled plug wires (by hand, no insulated anything) I was able to do so. Just grabbed the wires and pulled them off. Been a while since I tried that on a running car, and while my brain was flashing back to old days on the farm when we'd accidentally touch the 'lectric fence trying to get to the next field, last night there was no shock.

Are plug wires so well insulated these days that we can grab them?

These are new wires. Motorcraft 7mm from MAC's.

Regardless of the cylinder, it didn't seem to make a whole lot of difference. Slight decrease in the RPM (barely perceivable), but not much.

When I held the plug wire close to the plug the RPM went back to normal, but I never saw any spark, didn't feel any kick, and didn't hear any loud clicks. Did this on four different plugs (two fouled, two not).

Thinking electrical now. If there is *some* current, but not enough wouldn't it run, but not burn completely?

Bad Coil? Bad points, Bad condenser, Bad wires?

[Lip Ripper]

As I said before; a compression test will tell you a lot. Also, some cams require the 351W firing order. And I hope you haven't fried that new cam by running at such low rpm's on start up. Just take you time and eliminate the variables.

LR

[Groover]

Checked compression (cold) on cylinder #5 (previously routinely fouled) and #6 (not fouled). Both tested 150 lb of compression. If they test 150 lb cold, wouldn't they be even higher when it's warmed up? I can't get all the others tonight, but I'll get them this weekend.

Took the high tension coil wire off and held it to the block while cranking. Spark is orange? Isn't it supposed to be blue or white?

Checked point gap spark (turned ignition to run and set the points closed, then broke them with a screwdriver) and spark was there but not very strong (certainly not blue). Just a little static pop between them.

Started doing the tests in the shop manual for ignition. First five were ok:

Test #6. With the high tension coil wire grounded to the distributor, the voltage on the coil/battery terminal drops to under 6 volts. Book says it should drop no more than 0.1 volts? Not exactly sure what that one proves? but it failed.

Thinking all of this points to electrical and not valves, cams, carb, etc.

Either the coil, coil wire, the resister wire, the condenser or what?

[poboyjo65]

I bet Pop is lookin at a map to see how far it is to you!

[Groover]

I'll leave the light on for him, but a storm's a brewing over these parts tonight.

Thinking I'll swap the NAPA coil tomorrow since it has a warranty and they've been very good to me on this project.

That seems easy and will rule out one more thing.

[poboyjo65]

Have you moved the timing around ? while its running? I hate to keep harpin on this but if you dont tell us ,we dont know what you've tried.

[comethead]

Just an FYI, I've advanced the timing on my stock cammed 289 as far as 14 to 16 degrees BTDC without any issues or spark knock. (Although the idle was high). You can push it a little more.

Joe

[Lip Ripper]

That compression reading is a relief. Does your cam require 351 firing order or thre original? And it does sound like your spark is weak. Don't forget to run that baby around 2000 rpm for a while to seat that cam and lifter package. Good luck.

LR

[Groover]

Have you moved the timing around ? while its running? I hate to keep harpin on this but if you dont tell us ,we dont know what you've tried.

Sorry John. Yes, I started at 10 deg, then have tired 12 and now I'm on 14. It makes almost no difference when I turn it. Slightly higher RPM which slightly reduces the stutter (just because the RPM is up, I think). But even at 14, still can't rev it up without it trying to die unless we go very slowly.