• Hi Guest!
    If you appreciate British Car Forum and our 25 years of supporting British car enthusiasts with technical and anicdotal information, collected from our thousands of great members, please support us with a low-cost subscription. You can become a supporting member for less than the dues of most car clubs.
    There are some perks with a member upgrade!
    **Upgrade Now**
    (PS: Subscribers don't see this gawd-aweful banner
Tips
Tips

Pos>neg grnd, alt conversion...Tach issues

Share this page

64rocksprite

64rocksprite

Jedi Trainee
Country flag
Offline
Hi all,
I just fired her up after finalizing the pos-neg wiring and alt conversion (thanks to all for your help)
Everything seems good..but the tach is WAY off (too high) For instance while cranking it over, it is showing 2K rpms.. and I can give it a goose once running and its at red line (most in reality is 2-3K )
I did swap the wires on the induction loop and swapped the soldered resistor inside the guage per one of the "how-to" sites on swapping the Smith. At least I sure thought I did it right..
Anyone else experienced this? Help!

Thanks,
Devin
 
Devin

You most likely rolled the wheel on the adjustable potentiometer (sp) That little yellow wheel thing inside the tach is how you adjust it.
The ideal situation is to drill a 3/8 hole in the back of the tach housing in line with the pot so you can have it hooked up in the car and still get a small screwdriver in there to adjust it.
Or remove the guts from the housing, hook them up to power, coil, and ground, and adjust the wheel. Use a tach/dwell meter to get it right.
 
What spritenut said, but I would set it when running around 3k with the tach/dwell meter. I initially set mine to match at idle and found it was still too high when running at a usable range. At least that way you can use the tach as a shift reference, and set your idle with the tach/dwell meter, which is likly a more modern and accurate instrument.
 
65sprite and spritenut,
Thanks..I went and bought a timing light with RPM (man they get cha for that feature)..sure enough, adjusted the potentiometer..and dialed it in..It was running at about 2K..so I adjusted it there. seemed to follow once I goosed it to 4k..
I did drill the back so I could leave it all hooked up, not sure how one would do it otherwise! That adjustment is REALLY sensitive.
Now that that's done, I checked the volts across the battery with a multimeter..I was showing 16.3V..seems a bit high doesn't it?
The battery was run down a bit as I was starting and running the car on the battery (gen/regulator shot) before I converted to an alternator. Is it showing 16V because its charging a low battery?
Thanks for all the help..I'm hoping to finish the new headlight wiring and relays this weekend..and maybe go for inspection and plates this week..First inspection in 15 yrs!!
 
I'm a little concerned about that 16 volts. It should be charging at a constant voltage of 14-14.5V. Are you using a digital voltmeter? Sometimes electrical noise in the system can upset a digital meter.
 
Steve,
It is a digital meter.
The alt is a rebuilt unit..and I had it tested at AZone before installing..put out 14.3V on the bench test. Guess I'll call it interference..and watch the battery doesn't boil over!

Thanks,
Devin
 
Here's something you can try, for a couple bucks worth of parts from Radio Shack. The resistor and capacitor will filter the electrical noise. The values are not critical; in fact, you could go up to 470K (that means 470,000 ohms) resistor or up to 10 microfarad capacitor--the higher the values, the better the noise filtering--but the meter response will slow down somewhat. If the capacitor has a voltage rating, be sure it is well above 15V; 25V is good. You'll probably want to get an extra set of plugs to fit the meter, so you don't have to butcher the test leads. Also, this works only for voltage measurements.
 
Back
Top