I'm sure at my age I should know this but, how do you hook up a dwell meter to my 400 78 Trans Am. Also where is the best location to hook up a vacuum gauge to check the vacuum. Any help will be appreciated. Thanks.
Dwell meters are not used with the High Energy Ignition on a 78 model. Contact points went away in about 1973. So theres no need for a dwell meter. Connect your vacuum gauge to full manifold vacuum. If you will not be driving the car while checking vacuum, the transmission modulator line can be disconnected and used for that if no other full manifold vacuum sources are readily available.
I really just wanted to use the meter to adjust the carb.My meter has a tach on it easy to read while under the hood.Guess I'll have to find another way. Thanks for the help.
I'm not sure if the HEI would hurt your dwell / tach, but you could pull the coil cover off the distributor and connect to the tach lead (see "tach" mark atop the cover). Or make a little pigtail to clip onto the connector with the cover on. + to that, - to the air cleaner stud and try it. I am aware that some of those cars had tach adapters or something but you could try this if your dwell meter isn't an heirloom!
the hei will not hurt your meter. the tach post is only 9 - 12 volts. the high voltage comes out of what would be the big black coil wire on a std non hei and goes to the center post of the distributor cap.there may be a full time manifold vacuum port on the dfront drivers side of the carb. you can use that.your distributor is commonly connected to ported vacuum which is on the front passenger side of the carb.if your cam is stock i would start with idle timing at around 10 degrees, if it has a high perf cam then around 12.
Sorry double posted
By doing this little project you can also check the distributor module for proper dwell. There was article here some time ago that laid out this test. You can probably find it with a search.
Thanks I appreciate the help.
The positive lead on the dwell meter goes to the positive post on the battery or any positive terminal to supply power to the meter, the negative lead on the meter (black) goes to too the negative side of the coil to pick up the response from the points. In your case, connect the negative lead from the meter to the tachometer terminal on the HEI distributer cap. Unless you have a point ignition, I had to go back to points, couldn't use an HEI due to my tri-power and the electronic upgrade I put in kept giving me fits. Any vacuum line directly into the intake is best, not the carb. Using the tach. on the dwell meter is a good way to set the carb, I normally start by backing out the mixture screws out about one full turn unless the engine stumbles, in that case I turn it back in a little, then set the idle as low as I can and still keep the car running smooth then turn each mixture screw in slowly till you just feel it stumble or misfire, then back out 1/2-3/4 turn.I normally repeat the steps twice due to one will/could have an effect on the other.Good luck
adjusting idle mixture with a vacuum gauge works also..turn out idle mixture screw until highest vacuum reached. turn in till vacuum just starts to drop.. turn back to the exact point it starts to drop. do other side.. back until highest vacuum reached.. then in till it starts to drop. again turn back until you get to the point where it first starts to drop.. first screw again.. second screw again.. if the idle speed it too high or too low.. reset the idle speed screw.. readjust the idle mixture screws again..once you have gotten the idle mixture screws to the exact point where the vacuum starts to drop.. turn each screw in a fraction.. while watching the vacuum gauge.. you will have to judge it.. but you want the vacuum to drop 1/2" OF VACUUM total FOR BOTH SCREWS turned in slightly...this gives you lean best idle.. and has been the way mechanics have been taught until the advent of feedback carbs and fuel injection systems.. you can perform this with a tachometer.. but its much better with a vacuum gauge..
wayne is right, the vacuum gauge is your best friend, my methods are from years of experience tuning dual quads and tri-powers before electronic ignitions and when cars came with a vacuum gauge.
Thanks gastiresoil, for posting the correct way to connect a dwell meter. I had forgotten over the years.
Get'n old aint for sissies, next I'll probably forget how to hook up the timing light. I do remember getting juiced by the stupid little allen wrench that came with the new points when I missed the hex on the points and shoved her home a little too deep. Remember charging up the condenser and handing it to your buddy, that was some funny stuff, or having them pull off a plug wire while it was running after watching me do it.