[muzzfactor]

Hey guys, all my spark plugs are fouled out on my truck (84 GMC). They are completely black with soot. What does this mean? Thanks.

[carsavvycook]

Running too rich.

Possibilities also include, weak spark, low compression, spark timing too retarded, wrong spark plug, plug gap, wrong plug heat range.

What engine, what heads are on it, and how many miles were they run?

[muzzfactor]

It's a late 70's modlel 350. I did a compression test and all cylinders are at least 160. Not sure about the heads, but have never had a problem with it since it was rebuilt 30,000 miles ago. The plugs didn't even have 100 miles on them. They were the AC R44t, but i switched today to the r45ts gapped at 45. I've got an Edelbrock 1405 carbureator on it also.

[carsavvycook]

Is it a HEI, or points distributor? During the previous tune-up, did you have to adjust the timing?

Either way, look at the harmonic balancer. The rubber between the hub, and the outer half could be cracked enough to allow it to spin a little bit. This will move the 'mark' on the balancer away from the 'zero' mark on the timing tab.The only way to check this is to bring #1 piston to TDC compression.

I'll bet that 1405 Edlebrock Carb, needs a couple of adjustments.

What port did you hook up the distributor vacuum to? Manifold, or Ported?

[techinspector1]

Have you changed fuel pumps? If so, did you re-check the pressure at the carb? 5 psi is all you need.

[SDLuck]

1405 carbs have no tubes for manifold vacuum,which may be part of the problem,what is your timing set?You can adapt a manifold vacuum source from the pcv port.

[carsavvycook]

Originally Posted by SDLuck

1405 carbs have no tubes for manifold vacuum,which may be part of the problem,what is your timing set?You can adapt a manifold vacuum source from the pcv port.

Thanks for reminding me I forgot about the 1405 not having that port. Most of the Edlebrock carbs I have worked on lately are 1406's.

[muzzfactor]

I have an HEI and the vacuum advance is currently running off of the carb, which after reading many posts I believe that I should be running it off the manifold......correct? What vacuum lines should be running to the carb? Tomorrow I'm going to plug the two on front of the carb and just use the pcv in the middle of the carb. This carb was just rebuilt last week and seemed to be running better before I took it in. I will definitely take a look at the harmonic balancer also.

[carsavvycook]

Just make sure you have manifold vacuum to the distributor, and if you have a vacuum gauge, post your manifold vacuum reading at hot idle.

This will help us identify your problem.

[runn141]

on a 1405 edelbrock the vacuum port on the right hand side facing the carb is the full port vacuum, same as the intake. the stock fuel pump will have pressure from 7 to 9 psi. ive already experienced this with the same carb and had to install a regulator.

[Henry Highrise]

Sounds to me like you are gasing your plugs....carb float set too high? Choke not opening all the way? Carb air/fuel mixture not set right? Fuel pressure too high and over riding needle and seat? You have something giving you a rich condition....thus the black sooty looking plugs.

[SDLuck]

1405 made at this time, do not have a manifold vacuum port, only ported and pcv.

[SDLuck]

Ck vacuum ports with a vacuum guage,ck vacuum advance to see if timing is changing,What is timing set at and what is total? Is the intake manifold sucking oil from the bottom of intake,what is engine vacuum at idle? Give us some more information?

[muzzfactor]

Hey guys, I took the carb to a carburetor shop and they made sure everything was okay then I made sure and used the vacuum straight off the manifold and now it's running GREAT!!! I didn't have anyway the check how much vacuum i'm using but she's never ran better. Thanks for all your help guys.