Wacky Tach

[notny41]

I just put a tach on my car and some funny stuff happens when I am cruising at about 65mpg. The tach measures just over 3 grand and if I hold the throttle steady, the needle will twitch downward and back up to around 3000 again (kind of intermittently). The one thing I have found is that if I give it a little more gas when it starts its twitching, the twitching immediately stops and the meter returns to proper measuring. I don't feel any missing when the twitching starts. Wierd.

 

[slackr]

You running points?
Check the dwell/gap.
I had this problem, too... I then knew my points needed adjusting/replacement.

 

[notny41]

I do have points. Not long ago adjusted the dwell. Good to know - thanks slackr.

Last night I went out and tightened the + and - connections on the coil (both were fairly tight already) but I snugged them up even more and today I didn't notice the jitter. If that was the case, I wonder why it only did it at 3100 or so RPMs?

 

[slackr]

If my point dwell was too long, I would get a tach bounce @ lower rpm, too short and I got one up high.... I cannot explain your 3100 rpm bounce with this in mind in that it seems middle ground. The only other thing that comes to mind is that maybe capacitance had something to do w/ the rpm range combined w/your loose connection.

 

[notny41]

Well, the connection was not the problem. I just messed up on the RPM range. It still is doing it around 3500. But again, if I give it gas the bouncing goes away.

I'll recheck the dwell.

P

 

[charlies]

going o.t. here, look out.....

every time i see the title of this thread in the list of threads, i think,"he should have titled this thread 'wacky tachy' ".

 

[Max Power]

Maybe it's time for a Pertronix?

 

[jesserose17]

My tach bounces around, too, most of the time... and I have Pertronix! I have checked everything and still can't figure this out.

 

[VictorII]

I just put a tach on my car and some funny stuff happens when I am cruising at about 65mpg. The tach measures just over 3 grand and if I hold the throttle steady, the needle will twitch downward and back up to around 3000 again (kind of intermittently). The one thing I have found is that if I give it a little more gas when it starts its twitching, the twitching immediately stops and the meter returns to proper measuring. I don't feel any missing when the twitching starts. Wierd.

Do you have a spark box on your car? If you have one that produces multiple sparks per combustion stoke, it will make the tack act weird because the tach is connected to the coil which is where the spark box connects. The other thing to check is how well grounded the tach is. I bolted mine to the speaker grill with a long screw and it stays grounded well. Also make sure that your eyelets are crushed to the wires so you get good connection. Since it happens at a particular RPM, I'm thinking vibration......

 

[HistoricMustang]

Yes, check your grounds.

HistoricMustang
www.historicmustang.com/tech.html

 

[notny41]

going o.t. here, look out.....

every time i see the title of this thread in the list of threads, i think,"he should have titled this thread 'wacky tachy' ".

Charlies - I thought about naming it that - I like your car

I rechecked the ground too. I have it grounded to the dash. Maybe I'll solder the connector that connects to the coil.

Ozsum2 thinks it may just be the tach. Which I'm leaning towards. It was an untested ebay special.

I just don't know why it would stop flickering once I hit the gas