Spark Plugs What is wrong?
 

Ok...really does not miss...just runs ragged. These plugs are in order as
I took them out. From left top..1 3 5 7 and top right 2 4 6 8. Three of the plugs look like have never been run. Why are the center plugs that clean?
I have tried two diff carbs...two hei's and two sets of wires that I know run well.
Also...adjusted valve lash and it does not have a flat cam. The 350has a small cam...and 15 inches of vacuum. Pcv valve is good and has a baffle. Any ideas?
I guess next is to pull intake manifold...?

Re: Spark Plugs What is wrong?
 

How long were the plugs in the engine?
You are running mis-matched plugs (AC Delco vs Autolite)
The four that are black are beside each other in the firing order (may or may not be an issue) 1,8 & 7,2
When does the engine run ragged? at idle, just off idle, etc.
What carbs are you trying?
Did you just put the cam in it & what cam is it?
Did the engine ever run good?

There's no need to pull the intake unless you know you have a vacuum/coolant/oil leak.

Back up & start with the basics. Make sure you are not trying to tune a dead engine.

do a compression test
do a COMPLETE tune up.
install new plugs ( all of the same mfg)
new cap, wires & rotor
confirm correct firing order
go from there (it may be a fuel issue)

Re: Spark Plugs What is wrong?
 

Okay...just bought the truck...running this way...compression test already done
and is good...I have had all ac plugs and made no difference...both carbs run
perfect on my other truck...1406 stock eddy and stock600 holley.
The cam already in engine...214 at .050 and 456 lift. One is a new msd street fire and the other hei is good I know runs perfect..been carrying as a spare...fires right up and idles well..its mid range and low on power almost like a wire is off...but not quite. Really does not smoke. Throttle response is good...fuel pump has 5 pounds of pressure. So you tell me? :)

Re: Spark Plugs What is wrong?
 

Sounds mechanical:
That vacuum is quite low like a tired motor. Did vacuum gauge needle bounce or move while truck was running?
Do a leak down test to rule out rings seats, etc on those cycls. The autolite tells me that cylinder has had issues for a while and its not carb related.

Anything else is purely speculation and the lack of wanting to do any diagnosing.

https://mobiloil.com/en/article/car-...-leakdown-test

Re: Spark Plugs What is wrong?
 

Does your intake manifold by chance distribute fuel to the inner ones from one side and the outer ones from the other? Then you could have a problem on one side of your carb. But you'd have to look at the layout of the manifold to know for sure...

Re: Spark Plugs What is wrong?
 

Timing!!
What's initial timing?

Re: Spark Plugs What is wrong?
 

What's the gap on the plugs?...should be 45

Re: Spark Plugs What is wrong?
 

Do a leak down test sounds more like a mechanical issue. Also check and make sure that the power feed for the distributer is a full voltage and not the factory resistance wire.

Re: Spark Plugs What is wrong?
 

Cyl 3,4 and 6 all look like water contamination within the combustion chamber...

Compression test and leak down test...most likely blown head gasket between 4 and 6...

Could also be a lean out due to manifold crack...is this a two barrel or four barrel carb?

Open plenum manifold or closed ?

Re: Spark Plugs What is wrong?
 

I would get a correct set of matched plugs gapped correctly and run it again before you get too crazy trying to diagnose whats wrong , the threads don't even look the same length let alone the heat range can't be the same .:chevy:

Re: Spark Plugs What is wrong?
 

Is it a trick of lighting or camera, that Plug #2 looks 1/4'' shorter than Plug #1?
On closer look, you have 5 ACs and 3 Autolights. Running ragged, I wonder why?

Re: Spark Plugs What is wrong?
 

Timing is around 8 degrees with advance unplugged....

Re: Spark Plugs What is wrong?
 

GAP is .045 for the hei distributor.....

Re: Spark Plugs What is wrong?
 

Manifold is edelbrock performer bought new from oriellys by the guy I
bought truck from....carbs are not the problem both that I have tried run
perfect on my other truck.

Re: Spark Plugs What is wrong?
 

I have replaced numerous plugs...at first all were ac plugs.

Just bought a few autolites to try...made no difference.

Re: Spark Plugs What is wrong?
 

I had all the same at first...they looked fouled so bought all new ac plugs at beginning...no difference...then this last try...I put in the 3 autolites...still ran the same.

Re: Spark Plugs What is wrong?
 

Bump your initial timing up 6 degrees.
Your timing marks might be wacky.

Re: Spark Plugs What is wrong?
 

its easy to mix up 5 and 7 when hookin back up the wires.

Re: Spark Plugs What is wrong?
 

OK, so you know what is good, you can eliminate those. It narrows it down to a timing issue or a mechanical issue. Do what Geezer said: bump up your initial timing (I'd dial in as much as you can, if it begins to "hard start", back it off a little. Also confirm your timing mark.

If it has run like this since you bought it then you are chasing someone else's rabbit. There is a possibility that the cam was installed out of time. What heads are on it? If the heads have dual springs I have seen one spring break & the engine runs fine but doesn't run well up top. (the remaining spring keeps the valve operating & quiet, but "floats" at higher RPMs)

I'm hoping it's a simple timing issue, sure you are too!

Re: Spark Plugs What is wrong?
 

Well today I noticed the water down just a little in the radiator...so added some...let it warm and open the thermostat...guess what big bubbles
in the flowing water....never stopped doing the bubbles....it has turn down
tailpipes so I couldn't see the exhaust.

Re: Spark Plugs What is wrong?
 

I think they are the wrong plugs, you might need long reach plugs, I ran across same issue, took me 2 years to figure it out. use a thin wire with hook on it and put in hole for plug and see if it needs a longer plug.

Re: Spark Plugs What is wrong?
 

Do the spark plugs screw into the heads at 90 degrees to the head or are they angled off center ?

Taper seat or (peanut) plugs are meant for heads that have angled spark plug threads....if the spark plugs thread in at 90 degrees to the crankshaft, these plugs are the wrong type...they may be the same as what was in there, but that doesnt mean they are correct...

Post a pic of the side of the head showing the plug without the boot ....thanks

:chevy::chevy::chevy:

Re: Spark Plugs What is wrong?
 

...plugs look like a mix of brands and not the original sizes.....
Sounds like your basic parts group otherwise is in good shape so far....but you have some troubleshooting work to do.
I think the 15 inches of vacuum is probably ok, depending on what rpm you were at.
More important was the 'needle behaviour'...ie: steady? bouncing? intermittent drops? or?
...do the timing first....as Geezer said, bump it up.
Then I would look like mad for a vacuum leak somewhere....brake booster?...intake manifold?....carb insulator gasket?....open port or line?....broken vacuum hose?
...more pics?

All good
Coley

Re: Spark Plugs What is wrong?
 

While everyone has already mentioned the differences in plug brands and sizes, there is also a chance they are of different heat ranges too.

I've used hotter running plugs to compensate for poor oil control in the past.

Re: Spark Plugs What is wrong?
 

Sounds like you know what this means...sorry man. Maybe it'll be the gasket between 4 and 6 like Aussie speculated. Not a terrible job to do.

Re: Spark Plugs What is wrong?
 

Just curious, you're running an Edelbrock carb. Are you still running a stock fuel pump, or a low pressure pump? Stock pumps put out too much fuel pressure.

Re: Spark Plugs What is wrong?
 

He has bubbles everybody.

I had a head issue I got through this time last year. I had a plug that was stuck, wrung it off flush, removed head(s), magnaflux found crack, better performance rebuilt heads, I'm a happy camper. Hopefully it's just a gasket for you. I guess my plug was rusted in from coolant. Truck never smoked and ran great till I broke the plug while removing to take the header off to access the brake line/hose union better. Talk about a snowball! Good luck!

Re: Spark Plugs What is wrong?
 

I'm pretty sure that beginning in '71, taper seat plugs were used on SBCs, and went straight in, not in angled seats.

Re: Spark Plugs What is wrong?
 

Apparently we're the only ones besides the owner that realize his engine troubles go a little deeper than fuel and spark.

Re: Spark Plugs What is wrong?
 

Yep...he has a constant bubble stream in the radiator...obvious water ingress into at least three cylinders...and an engine running like KRAP...

Pull the heads and take a look...

Post a pic of the heads once they are off...

Then we can all see what the issue really is...

:chevy::chevy::chevy:

Its a Chevy...its not rocket science...

:fb::fb::fb:

Re: Spark Plugs What is wrong?
 

Yes..thanks guys for all the comments....I am presently working on wiring....
soon will pull the heads...will let everyone know what I find...thanks...Tim

Re: Spark Plugs What is wrong?
 

You can confirm the presence of combustion gases by having a shop place their emissions analyzer sniffer above the filler neck, if "HC" readings go up, bingo!
Not all head gaskets leak coolant into the oil, some leak into the intake passages. I'm surprised this engine isn't running hot....if you cannot maintain system pressure in the radiator, the boiling point of the coolant goes way up, placing a vacuum on water does just the opposite, lowers the boiling point.
That's why you keep a pressure cap on the radiator. 15-16 psi is normal, should raise the boiling point to 230-240 degrees.something like that.
You haven't noticed any unusual smoke/steam coming out from behind when you accelerate have you?
Hope it's an easy fix, I'd be looking for cracks in between the combustion chambers or maybe it's just a gasket issue.
Hth,
Ben
:metal:

Re: Spark Plugs What is wrong?
 

^^^ This. I've used a buddy's SnapOn emission sniffer for this. I put it on CO (not HC, though maybe either works) and sniffed the filler neck, and even in a car where the leak was slight enough that there were no visible bubbles, the CO count would shoot up when placed over the filler neck.

Re: Spark Plugs What is wrong?
 

I stand corrected! Knew it was one of the two!
Ben