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Discussion Starter #1
Just wanted to get some opinions on my tach bouncing around 200-300 rpm at lower engine speeds (<2000 rpm).

The tach jumps +200-300 rpm sharply at random times, but the engine is not following these jumps. Two different tachs have responded the same way. At higher rpms (>2000) the tach runs fine and the motor pulls hard. Is it possible there is some cross firing going on at lower rpms?

My ignition setup:

Mallory Unilite mechanical distributor
Mallory canister coil
8 mm Taylor spark plug wires
NGK V-Grove spark plugs

If you need more info on the motor just let me know.
 

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could be electrical interference from the coil, you might want to try a resistor in the wire going to the tach.
 

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You did not list the maker of the tach you own. Is it a cheapy, or $$$$$...?

You are not using an ignition module...? just the signal striaght from the coil?

If so, the duration of the signal at low RPM's maybe smaller then the tach wants to see, so it is doing it's best to count short ignition pulses.

Call the MFG of the tach and see if there are any other reports of this, and if it is normal. It maybe normal for the make of your tach.

<font size=-1>[ This Message was edited by: Mikes66 on 6/1/07 12:18am ]</font>
 

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Discussion Starter #4
On 2007-05-31 09:17, Mikes66 wrote:
You did not list the maker of the tach you own. Is it a cheapy, or $$$$$...?

You are not using an ignition module...? just the signal striaght from the coil?

If so, the duration of the signal at low RPM's maybe smaller then the tach wants to see, so it is doing it's best to count short ignition pulses.

Call the MFG of the tach and see if there are any other reports of this, and if it is normal. It maybe normal for the make of your tach.

<font size=-1>[ This Message was edited by: Mikes66 on 6/1/07 12:18am ]</font>
Currently I'm running a cheapy tach (brand unknown), but also my MAC Tach/Dwell tester did the same thing.

The signal is coming directly from the negative side of the coil.

Maybe a good reason to buy a better tach?
 

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Discussion Starter #5
On 2007-05-31 08:56, 67stang wrote:
could be electrical interference from the coil, you might want to try a resistor in the wire going to the tach.
Although I might buy a new tach, I'm interested in how much resistance I should run between the coil and tach to test this?
 

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Stewart Warner gauges.............2 year warranty and made in the USA not overseas. http://www.4secondsflat.com

$199 for water, oil, voltage guages with a chrome pod.

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http://www.spalisautodetailing.com/

Stroker Video http://www.spalisautodetailing.com/project/index.htm

70 Mercury Cougar 347 Stroker(415HP/440TQ), Tremec TKO 5 speed, Ford 9" w/3:55 gearing
My engine builder http://www.flowtechnicsonline.com/

<font size=-1>[ This Message was edited by: Spali32 on 6/1/07 3:22am ]</font>
 
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