V8 350 question

[R@nger]

I've brought my 350 small block a long ways since when I got it a year ago. When I got it, it ran horribly but after a good bit of work it seems to be running really good now however I have a question. It wasn't until about, mmm 1-2 weeks ago that my truck saw road time since I got it. I took it to get exhaust and to get emissions tested. Anyways I decided to pull the plugs and found something kinda weird. I started taking them with the right one ad working my way back. The first 3 were all tan and looked good but the last spark plug on the right side was a little blacker. I made a mental note then proceeded to take out the left side spark plugs. The first plug was one that was older than the others because I broke the previous one. It was a little blacker than I wanted it but not horrible. The middle two again were tan, but the last one was noticably blacker than the previous ones on the left side. I started wondering what might have cause this. Any ideas? Could the timing be off?..., I'm thinking it's something either with the timing or its something electrical.

Any help would be awesome, thanks!

[CHEVIBUBBA]

you using the stock intake manifold?
some manifolds, especially stock ones are notorious for improper A/F distribution to the cylinders.
check your plug wires.is it dry black & smell like fuel or wet black & smell like oil?
if your plug gaps aren't right or the heat range is off it can cause similar reads.
could also be valve problems.
i suggest a leakdown test & an upgrade to a performer rpm airgap.
it has better A/F distribution to the cylinders.
best would be mpfi if you can afford at least $2k

[R@nger]

It's the stock manifold.

The plugs..well the two end one I mentioned are a dry black..like carbon buildup.

I know all the gaps are fine because I cleaned and gapped the plugs about a month ago.

Whats a "leakdown test"?

[Blazer1970]

If it has a Q-Jet, it could be starting to drip fuel out the plugs in the bottom of the fuel bowl. When this happens, un-atomized fuel drips into the intake and it runs to the back cylinders since that is the way the engine leans. This causes a rich condition at the rear cylinders and fuel fouled plugs like you describe.

[71-longbed]

interesting ...

i never understood why a larger gap would yield better economy but less power ...

[67chevemall]

start new so you know what you got.
plugs wire cap rotor intake manifold, carb rebuild.
0.02

[R@nger]

I rebuilt the carb not long ago at all...and yep it has a qjet.

[R@nger]

ttt

Any more idea?

[JimKshortstep4x4]

I believe that Blazer1970 has come up with the most likely cause. The plugs on the Q-Jets do leak. Did you epoxie the plugs when the carb was rebuilt?

Jim

[R@nger]

Nope I didn't epoxy the plugs. I was unaware I had to.

What plugs are we talking about here..I'm a bit confused.

I know ya said the plugs at the bottom of the fuel bowl but I thought the fuel bowl was the little black bucket looking thing...I don't seem to remember plugs being in it. I rebuilt it last summer so again I don't exactly remember.

[GloryHound]

The first question I have to ask is how old are the plugs. If they are older plugs get new. Same thing with the wires, cap, and rotor. Are you running points, these can get a little tricky to set just right and need fairly constant attention. Then we can go from there into more costly and time consuming problems.

[R@nger]

Ok the plugs are...maybe 6 months old, the wires are brand spanking new(Accel 8.8 spiral wound), I have HEI ignition and I'm not exactly sure how old the cap or rotor is.

[Blazer1970]

Originally Posted by R@nger

Nope I didn't epoxy the plugs. I was unaware I had to.

What plugs are we talking about here..I'm a bit confused.

I know ya said the plugs at the bottom of the fuel bowl but I thought the fuel bowl was the little black bucket looking thing...I don't seem to remember plugs being in it. I rebuilt it last summer so again I don't exactly remember.

The bowl plugs are in the bottom of the fuel bowl in the carb. They look like little aluminum freeze plugs. They are in the bottom of the main body (center section, between the air horn and the throttle plate) of the carb. To access them, you have to remove the throttle plate from the bottom of the carb (remove the two long back screws from the top of the carb, and two phillips head screws from the bottom). Then clean up the area around the plugs with a file and coat them over with some JB weld. They are VERY prone to leaking, and will cause the EXACT symptom that you are describing.

[RainFade]

How about some pictures ?

carcraft q-jet rebuild article