Re: Tom tuned his carb??!!

[Tom Mandera <tsm1@domain.elided>]

"John A. Landry" wrote:
> 
> If you don't change anything else (like switching to premium fuel), my
> experience has been that the pinging is best controlled by retarding your
> timing a bit.  You might try 5 to 7.5 degrees BTDC instead of the 10
> degrees you have now.

That's what I thought.  I remember hearing it ping back when I first
bought the '72.. but that I haven't heard it since... up until last
night, I was running #61 jets and I had never heard it ping... but I
also never had the motor accelerate *smoothly* under load... ;-)

I put the #59 jets in with the new carb, and now that it accelerates
smoothly I get a ping when I'm on the throttle hard.

I wonder if it *is* running lean and *that* is why I hear the ping, or
if it's just the timing is too far advanced and it's the SMOOTH
acceleration that's making it ping (vs the "all or nothing" throttle
response previously)

> run a *really* lean air / fuel mixture you will certainly get pinging under
> slight to moderate load conditions.  However, once the air / fuel mixture
> is in the proper range, pinging is controlled to a greater degree by timing
> (for a given fuel octane rating).

I guess I need to find the optimal range still.  I had #58s in the old
carb and hit 13mpg and could maintain 75mph and climb mountains without
pinging... and I don't remember it in town before (again, could be the
smooth throttle response under hard acceleration I now have that I
didn't before)... the 59 jets are an attempt to get back closer to that
13mpg figure *and* not lose as much umph.

I'll be bringing the 61s with me next weekend... in case the 59s are too
lean for towing...

> BTW, the vacuum an engine has at any given rpm and load is not very useful
> for comparison purposes against other engines.  Each engine will have a

I threw the # out (16") in case that's a bit low... the nifty "Engine
Tune Up Diagnostic" kit has a vaccum gauge with both degrees (inches of
Mercury) and "zones"... it's currently (@ 16) in the "late ignition
timing" area... but.. I suppose the gauge itself is for the general
"idiot" and not a particular vehicle.  However, the "Kit" is from the
70s, and so is the truck. ;-)

I think I'm around 4,000' here.. I know vacuum goes down as you go up.. 

Something's really "up".. the last few days I found myself rolling at
stop lights and the brake pedal would drop.  I attributed it to the
warped/untrue rotor assembly on the driver's side that's making the
"bounce/jerky" stopping... I thought maybe I let up the brake just a
little and the truck rolled just a little, and hit a "low spot" on the
rotor and *that* was why I rolled forward... well, this morning it
occured to me... the mastercylinder appears to be leaking down.  I'll
double check tonight, but... Argh.

(FWIW, the untrue rotor is coming back off this weekend.. I had to put
it on in a pinch two weeks ago when I screwed up the new wheelbearing
grease seal on the "true" rotor at 11pm)

Leaking m/c and towing down passes = BAD IDEA. ;-)

-Tom