Tach

gsharapa · 04-06-05, 11:30 PM

Was wondering if you guys with GTD GT40s have had any problems with your original Tachs? Mine is not accurate and runs very high. Checked the ground on engine to frame, which is good, and connection from coil is good. Any ideas or do you think it is just the Tach itself?

Paul Thompson 'Hooligan' · 04-07-05, 06:00 AM

Hi Gary
How high is very high? and is the reading in error by a fixed percentage throughout the range?

gsharapa · 04-08-05, 10:03 AM

It appears to be double like it shows 2,000 at idle and then just doubles all the way up. I know years ago the old tachs had settings for 4, 6 and 8 cyl and if you were on a 4 cyl setting with a V8 you would get reading like this. I haven't pulled the tach out yet to see if there is anything like that. Thought I'd put a post up first to see if anyone experience this with their GTD Tach or not?

Paul Thompson 'Hooligan' · 04-08-05, 10:31 AM

you're not running a wasted spark system are you? [img]/ubbthreads/images/graemlins/smirk.gif[/img]

if so - each cylinder will see a spark on each rev - compression and exhaust, which would double the tach output signal...

If you have a multimeter with an rpm reading available, clip it on the same wire feeding the tacho and see what it reads.

Let us know how you get on. [img]/ubbthreads/images/graemlins/smile.gif[/img]

gsharapa · 04-08-05, 12:29 PM

Paul,

Just running the Mallory Unilite Distributor with a MSD blaster coil. I actually hooked up a tach/dwell hand held meter to directly to the coil and it seemed to report correctly. It probably is something in the tach or the tack and the Mallory are not working right together. I most likely will take the tach out and take it over to my buddies race shop and hook it up to one of the Cobra there and see if it works the same way.