New Tach and dwell meter question

[Scottjeffrey]

I installed my new weber 32/36 DGEV today. It's running beautiful. Last week I bought a tach and dwell on Ebay in the box unopened! Manufacturing date, 1974 just like my '02.

Its scales are for 6 and 8 cylinder and you are supposed to double the 8 cylinder reading for a four banger. I wanted to check my RPM's under the hood while setting up the carb but was perplexed. The 8 cylinder reading was on 2 (200) x 2 is 400. The tach in the car read a hair under 1000. Any thoughts about this?  Glad my Innova 3658 timing light with tach is on the way but I'd love to figure out what's going on with my 'new' meter. Thanks so much!

Scott

[Roland]

Thoughts?  Your new-old analog tach was probably not known for its accuracy when it was manufactured,  It was an inexpensive unit not targeted toward professionals.  The more reliable/ accurate "professional" equipment was expensive.

Edited September 22, 2019 by Roland

[Scottjeffrey]

25 minutes ago, Roland said:

Thoughts?  Your new-old analog tach was probably not known for its accuracy when it was manufactured,  It was an inexpensive unit not targeted toward professionals.  The more reliable/ accurate "professional" equipment was not inexpensive.Unavailable

 

 

Could it be that it is simply that far off?

[Roland]

Unfamiliar with your device.  "Played" with similar gauges that were notoriously inaccurate, like cheap analog watches.  Sometimes the needle would stick and you would have to tap the unit to free it.  Unit could be affected by heat, humidity, vibration or even lack of lubrication.  Consider most analog watch movements are "jeweled."  Some were made with very few jewels, but the better watches have many.  Some jewels were made of semi-precious materials, others, not-so precious.  Those jewels also needed lubrication and were in sealed compartments.  But even the best watches occasionally require cleaning and maintenance to ensure reliability and accuracy.  You probably do not know how your unit was stored and even if it was a dry hermetically-sealed vault, gravity has an affect and older lubricants may dry out and not last indefinitely.

Edited September 22, 2019 by Roland

[Jimmy]

2 hours ago, Scottjeffrey said:

I installed my new weber 32/36 DGEV today. It's running beautiful. Last week I bought a tach and dwell on Ebay in the box unopened! Manufacturing date, 1974 just like my '02.

Its scales are for 6 and 8 cylinder and you are supposed to double the 8 cylinder reading for a four banger. I wanted to check my RPM's under the hood while setting up the carb but was perplexed. The 8 cylinder reading was on 2 (200) x 2 is 400. The tach in the car read a hair under 1000. Any thoughts about this?  Glad my Innova 3658 timing light with tach is on the way but I'd love to figure out what's going on with my 'new' meter. Thanks so much!

Scott

 

Scott,

 

A lot of these type of tools are not intended to be absolute but instead require a bit of calibration against a known reference. Reasons for this include manufacturing variances, differences in the scales for different modes of operation, operating temperature, and the cost associated with building around all of those variables.

 

See if it has as adjustment screw and then adjust it according to a reliable source. Ive observed the tach in my dash reads about 200 rpm low.

 

Cheers

[Scottjeffrey]

2 minutes ago, Jimmy said:

 

Scott,

 

A lot of these type of tools are not intended to be absolute but instead require a bit of calibration against a known reference. Reasons for this include manufacturing variances, differences in the scales for different modes of operation, operating temperature, and the cost associated with building around all of those variables.

 

See if it has as adjustment screw and then adjust it according to a reliable source. Ive observed the tach in my dash reads about 200 rpm low.

 

Cheers

 

Thank you, Jimmy!