HEI tach ('75) installed, engine off = 300 RPM???
01-21-2002, 06:23 PM
#1
Drifting
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HEI tach ('75) installed, engine off = 300 RPM???
I just installed my '75 tach to go along with the HEI distributor I've been running. When I turn the key to the "run" position without starting the engine, the tach settles at about 300 RPM. Also, it appears to be a little high across the board. I have disconnected my old Autometer tach, so I don't have a direct comparison, but my RPM at certain MPH in 4'th gear tell me it is about 200 RPM high across the board.
Should the tach be at 0 with ignition on/engine not running? If so, is there a way to calibrate these tachs?
Also, I do not (yet) have a tach filter, but that should just prevent random spikes.
Should the tach be at 0 with ignition on/engine not running? If so, is there a way to calibrate these tachs?
Also, I do not (yet) have a tach filter, but that should just prevent random spikes.
01-21-2002, 08:23 PM
#2
Le Mans Master
Re: HEI tach ('75) installed, engine off = 300 RPM??? (Chris A)
When you turn the key on without starting the ignition, the tach needle should be at zero. Do not know how your needle is attached, but my 82 needle was just pressed on a pin. Simple to pull off gently and push back on gently at zero. Emphasize gently.
01-22-2002, 12:14 AM
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St. Jude Donor '07
Re: HEI tach (Larry82)
Not sure how to adjust or calibrate, but should go to zero with engine off. Mine does, even when it dies and I'm still coasting. Might try what Larry82 says.
Edit: forgot to say when I turn the ign to off, the tach goes back up. Not sure why, it just does. So maybe try readjusting needle when the key is in run.
[Modified by Buffalo Dude, 8:20 PM 1/21/2002]
Edit: forgot to say when I turn the ign to off, the tach goes back up. Not sure why, it just does. So maybe try readjusting needle when the key is in run.
[Modified by Buffalo Dude, 8:20 PM 1/21/2002]
01-22-2002, 01:38 AM
#4
Re: HEI tach ('75) installed, engine off = 300 RPM??? (Chris A)
As the other posters have said... calibrating the tach to zero is as simple as - key on, engine off - set "needle" to zero on the dial. Yes, this implies that you're taking your dash apart again! It is also true that when the ignition is turned off the needle will float up to some other point until it is turned on again... I also believe my tach reads about 100 rpm too high (compared to the tachometer on the fancy timing light). Could be that I did not get mine right on zero when I changed my card the other year.
The other thing you will soon be introduced to is the tach filter... it is the little condensor looking item in the tach line coming from the HEI and clamped to the manifold... When they wear out the tach will read wide sweeps of the needle without the engine changing speed. The rumor is these are not available anymore and you have to build your own from Radio Shack parts... does not sound too complicated.
The other thing you will soon be introduced to is the tach filter... it is the little condensor looking item in the tach line coming from the HEI and clamped to the manifold... When they wear out the tach will read wide sweeps of the needle without the engine changing speed. The rumor is these are not available anymore and you have to build your own from Radio Shack parts... does not sound too complicated.
