Hotter spark/fuel octane

[Anonymous]

Please don't laugh if I'm bringing up a simple topic, but I'm on a learning curve here.

'82 stock 200 I-6, all emissions systems intact and working well. Carb set to specs, works great.

I just recently upgraded to a 'performance' coil. Accel can type. Definitely hotter than stock. Left everything else alone, even left plug gap at .050. Did not change timing.

Prior to this, I have been unable to run anything less than 93 octane w/o pinging and dieseling. Once in a while, I put in a half tank of 89 octane, and it was OK, but still dieseled slightly.

After the coil change, I am able to run straight 89 octane all the time w/o pinging or dieseling. Starts better, runs better, a little bit better mileage. Overall, it's a great improvement.

How come a hotter spark allows me to run lower octane fuel w/o problems? Wouldn't a hotter spark increase the likelihood of preignition, or am I thinking about this the wrong way?

I'm not complaining, I'm just curious. Maybe I can do a few other things to make it run even better on lower octane fuel.
I'd like to leave the timing where it is, since driveability is so good.

 

[CZLN6]

Howdy Doug:

A stronger spark causes a more complete initial burn. It will leave less chance for random detonations.

Pre-ignition- some source other than the timed spark from the sparkplug ignite a part of the fresh mixture. When that random flame front collides with the plug ignited flame front "Knock" occurs.

Detonation- Some portion of the fresh charge ignites in the recesses away from the spark plug initiated flame front. Again, when the two flamefronts collide, "Knock" is the result.

Solutions to reduce/remove Knock- Slower burning, higher octane gas, Elimination of chamber hot spots, Less initial advance, A chamber with a tighter quench, causing more turbulence and abetter, more complete, timed combustion. Cooler engine temp and a hotter spark can also help

I'm more curious why your '82 200 is so prone to detonation and dieseling? This engine was designed to run on regular gas octane ratings. What is your initial advance setting? Is your engine suffering from carbon build-up? Carbon deposits can act as glow plugs and cause pre-ignition knock, a close cousin of detonation. Reducing carbon build-up in the combustion chambers will help your situation in several ways.

Dieseling is usually caused, in part, by a too fast idle setting. Try reducing you idle speed.

Adios, David

 

[Anonymous]

Hey, that helps. Thanks for the feedback.

I thought about carbon deposits. I just need to 'decarbon' the engine and see if it makes a difference. I'm also thinking maybe the dampener has slipped a bit, and maybe I'm running more advance than I realize. That thought had occurred to me, too. I should just do it the old fashioned way; tweak it a bit and drive it, etc. until I eliminate the pinging. Lowering the idle speed has helped in the past with dieseling, too.

This forum has been an excellent source of info, and I knew I could get some good feedback here. Learning all the time. We're not having fun unless we're tinkering with it.

What has everyone used to remove carbon deposits? I keep reading about a half bottle of Seafoam sucked through a vacuum line while it's running. My neighbors are gonna freak when they see all that white smoke. Better do it at night. LOL