Carb/plug question

[Sonny]

I have a ‘78 360 engine with a 570 Holley carb, RPM airgap manifild, and Pertronix unit in my 70 Belvedere. My plugs are still white after going from #64 primary jets to #70 jets 3 days ago! Just drove the car from Florida to Charlotte and back. Plugs just won’t turn brown. Did I drive enough miles? Is the 570 just too small? I also have 19” of vacuum and a 8.5 power valve. Car doesn’t surge either. There is black dust on the rear of the car too.

 

[RJRENTON]

Sonny,
With regard to your question, several factors need to be determined.
What is the spark advance...initial, rate of advance and total ?
Are you using vacuum advance ?
What is the heat range of the plugs you are using now....brand or number?
What is the compression ratio of the engine?
What is the coolant temperature ?
What RPM were you cruising at?
What is the manifold vacuum at cruise RPM?
What type of fuel are you using...unleaded with an additive, leaded, is there alcohol in the fuel blend ?
The Holley carb you are using sounds to be OK. But perhaps increase the primary jetting a little more. A little more information will be helpful.
Bob Renton

 

[oldbee]

I go with RJ except I think the brown color ur looking for is from using leaded gas( what,where?). More tan/white is probably the norm now?

 

[Sonny]

Sonny,
With regard to your question, several factors need to be determined.
What is the spark advance...initial, rate of advance and total ?
Are you using vacuum advance ?
What is the heat range of the plugs you are using now....brand or number?
What is the compression ratio of the engine?
What is the coolant temperature ?
What RPM were you cruising at?
What is the manifold vacuum at cruise RPM?
What type of fuel are you using...unleaded with an additive, leaded, is there alcohol in the fuel blend ?
The Holley carb you are using sounds to be OK. But perhaps increase the primary jetting a little more. A little more information will be helpful.
Bob Renton

Thanks RJ. Here goes:
Timing is 12/36 with vac advance on top of that. 19” steady vacuum at idle. 3000 rpm avg on my trip. Plugs are whatever napa said a 360 took- nothing special- AC Delcos I think. I use premium gas, no additives. Engine never gets over 190 degrees. Don’t know specs of engine just was told it was a crate engine. One note relevant or not: On the highway doing 70-80 mph, and in cruise mode, the mufflers seem to make a rhythmic, surging sound, under power and when decelerating they (duals with H pipe) sound nice and smooth. Thought that was odd. Also last week before the trip, the plugs were a nice tan color. Hope that helps.

 

[lewtot184]

may have too many degrees in the vacuum advance. personally, I don't look for brown or tan on the porcelain. look for the timing on the ground strap. a/f is on the rim of the plug. plug may be too hot.

 

[oldbee]

I had a slight surge w/Chrysler electronic and backed off v.advance about 3*, fixed it.

 

[lewtot184]

I had a slight surge w/Chrysler electronic and backed off v.advance about 3*, fixed it.

I've put thin shims in the advance arm notch to limit total advance degrees. seems to work well. some of the vacuum advance units have too many degrees in them.

 

[idrivemopar]

Do you by chance see any black specks on the porcelain? If you do, that's an indication of lean.