Tune It Right
I've been a subscriber since Thunder Am. Awesome publication! Thanks. Please put these procedures to tune up a traditional Pontiac V-8 in order. Adjust dwell; set idle speed; adjust idle mixture; check advance at different rpm; set base timing; when exactly during this tune-up to have the vacuum advance disconnected and plugged; at what point in this order to put it back on; at what point in this tune-up do you check full advance reading; and anything I'm forgetting.
One more request please, I rebuilt a '69 Pontiac 400 that I purchased from an unknown source. It's relatively mild with an 067 cam, stock exhaust manifolds, stock iron intake ('68), and a rebuilt Q-jet. It has '68 No. 15 small valve heads, is 0.040-over, and I run an untouched stock '75 350 HEI distributor with direct battery voltage. It's an A/C car and has a mix of 2.25 and 2.5 exhaust with small stainless-steel mufflers. The transmission is a wide-ratio Muncie. It runs incredibly well, and with a 3.23 open rear I'm getting 16 mpg!
However, the timing (initial), reads so high it's almost off the mark. I suspect that the ballencer has spun slightly. Is there an easy way to tell, without taking the engine apart?
Thank you in advance for your help. The reason I'd like to see my letter in print is because it could certainly help many average skilled people like me who read your magazine. OK, maybe I'm a little below your average reader. Nonetheless, keep up the great work!
Steve (Rapp'n) Richer
Woonsocket, RI
Ray T. Bohacz responds:
You have some very good questions that are founded on procedure, but also require understanding. I'm a firm believer in that people who are the best at whatever they do have a complete comprehension of what they are trying to accomplish and how the system works. To that end, I will provide a brief overview of a tune-up.
When tuning an engine, a synergy needs to be established that often will have to be revisited as the process goes along. The specifications are not brought together digitally, but in an analog fashion. For example, if you decide to advance the ignition timing at idle, then the engine speed will increase and will require the throttle stop screw to be readjusted along with the mixture screws, possibly. Conversely, if you retard the timing at idle from the previous setting, the idle speed will need to be increased and the mixture may need some fine-tuning. This is due to the relationship of the throttle plate and the transfer port or slot in the carburetor venturi.
With this in mind, I listing the following steps. Alter them to meet the needs of your application or service procedure.
[Editor's note: Even though the engine mentioned has an HEI, this procedure will include steps for a points-type distributor as well, for readers whose engines still use them.]
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