Distributor Octain Adjustment

Doug_S · 09-12-05, 10:55 PM

Hi,

Does anyone know which way to adjust the knob on a non-usa distributor to advance the timing or retard the timing? Mine has some very vague markings on it that I can't really see that well. What I'd like to do is to retard the timing at higher engine speeds to adjust for the low octain fuel 'cause it's cheaper by .30.

Thanks in advance for the help!

red66toy · 09-12-05, 11:38 PM

Turning the dial towards "A"(on the dist) or away from the engine advances the timing. Turning it towards the "R" mark, or towards the engine retards it.

DocB · 09-13-05, 05:45 AM

Or if your marks are worn off you can use a timing light and see which way the mark moves. If the RPMs pick up at idle, you are prolly advancing.

honk · 09-13-05, 05:47 AM

Clockwise advances.

Make sure it's set to the zero line before adjusting with your engine timed to 7 degrees (0r whatever you use). The zero line is the one that extends further around the circumference than the others. The 'set line' is that one that goes the length of the adjuster.

Doug_S · 09-13-05, 09:28 AM

Thanks for the info, guys. I appreciate it. Now I can tune the engine for the lower octain gas.

Degnol · 09-13-05, 03:23 PM

Doug, at 7.8:1 compression, you should be fine with 87 octane as it is. Has the head been shaved or something else to raise compression? I don't think you need anything higher than 87 until you have compression of 9:1 or higher.

Ed

Doug_S · 09-14-05, 10:59 AM

For whatever reason, mine tends to predetonate on anything less than 92 octain. I think that over time, carbon has built up and raised the compression or, as you mentioned Degnol, the head may have been shaved during a rebuild. I'm going to mess around with the octain adjustment knob in the hope that it will solve the expensive gas need that I'm in.

Degnol · 09-14-05, 11:18 AM

There are some old school tricks to decarbonize engines. I think SeaFoam has an application, but we used to trickle water down the carb of a fast idling engine.
Have you done a compression test?
I think if you do have heavy carbon buildup on the piston tops, it gets very hot and acts like a glowplug.
I'd start with a good compression test, all plugs out, throttle blocked wide open and a good charge on the battery. Post up the #'s.

GL

Ed

PabloCruise · 09-14-05, 12:35 PM

Are you running very advanced Doug?

Not sure what altitude you are living at, but I'm around 5K feet, so I run ~15 dgrees initial advance at idle.

With a basic light, I can still see the BB in the bottom of the window.

When I first got back up and running, it pinged - BB wasn't visible. Backed timing off til I could see the BB - no ping, better running.

rgentry · 09-14-05, 08:23 PM

I don't think the octane knob does anything different than
changing the static timing by turning the distributor. If you
can't get it timed properly with the initial timing (set by
turning the distributor) then it is unlikely that adjusting
the octane knob is going to do anything for you.

Quote:

Originally Posted by Doug_S

For whatever reason, mine tends to predetonate on anything less than 92 octain. I think that over time, carbon has built up and raised the compression or, as you mentioned Degnol, the head may have been shaved during a rebuild. I'm going to mess around with the octain adjustment knob in the hope that it will solve the expensive gas need that I'm in.