The Stovebolt Site Forums The Shop Area Engine Shop Sparkplug color.

Ok, what happened to reading the spark plug color? I was doing a little work on the 4bbl carb on the 261 engine in my 37 truck. The plugs are a dull white color, I'm talking jetting for part throttle here, not wide open throttle plug readings.The engine runs great, in fact its slightly rich as the choke is not needed at all on cold start up at least on these warmer mornings.I checked a plug on my other "stock" Stovebolts, dull white after a good ride. None of these vehicles have lean carburation problems .In fact our regular driver early 90's fuel injected vehicles have white colored plug tips.Last year the plugs would color light grey. Maybe the gasoline formula is cleaner burning?This isn't a area requiring the special fuel blends as required in some states and the the Sunoco gas I buy here has no warnings on the pump about alcohol etc.

Any changes on the bike plugs?

Yes,The bike plugs are lighter in color.My bikes have magnetos ,which have a weaker spark at low engine speeds than a battery ignition, so the plugs are darker if you do a lot of riding around town. I have noticed over the last few years the bikes tend to run a little rich at idle, with the same timing and carb settings as used in the past while the plug color indicated a leaner mixture at higher cruising speeds.Other riders of vintage bikes report the same thing.The blame is put on fuel designed for newer injected vehicles, not so dependent on fuel atomization as on a carbureted engine?
For part throttle or cruising jetting,I jet leaner until drivability problems are encountered, then go richer until the flat spot is eliminated.Plug color is secondary in this case.Wide open throttle jetting is a different story.

is inflation and oil politics giving us lower octane gas?

Bill

Maybe political gas
tony, I think you are just keeping everything running in top condition

Tony - I've noticed the same thing - plugs are not coloring up as they did in the recent past - even with heat range changes. Must be the fuel blends have changed again.

I noticed similar results with my 4bbl/235 setup. The plugs would be white and the tailpipes black, no matter what jetting or heat range I was using. Somebody mentioned that part-throttle/cruising mixture on a Holley 390 was controlled by the air bleeds. Is this true?

What brand and heat range plugs are you guys running in 235s/261s?

Chip

Chiphead,A friend of mine who does carburetor work says yes ,the airbleeds are used to adjust part throttle fuel air mixture on Holley performance carbs.He says Holley offers a kit to convert the metering blocks to screw in air bleeds for easy part throttle mixture changes.Changing the main jets has little effect on part throttle performance.

Is that conversion kit available for a 4160 series carb?
Are we still trying to get the plugs a tan color, or is the white OK?

Chip

Just my $.02...

Here in the Eastcoast, we get the privelage of using Oxigenated Gas...This stuff breaks down fuel rubber lines and gaskets, seals and other things...causing fires, leaks and YES...white deposits on spark plugs...

Jim

Chiphead, I may have mispoken.Holley 4150 and 4500 carbs have replaceable air bleeds.He says to look up Holley.com, you can order a master catalog or ask questions.