24 replies to this topic

[mesrine]

6v terminal....

[dklawson]

regarding the rev counter reverse. the plain yellow wire is to the fuse box power source, both yell/green are earths, red is the light...
car is positive earth, and the counter is for 4 cyl.

.the coil picture, shows the spade to the distributor removed, and thats where i have inserted my pulse lead.....it shows the the pulse lead is inserted on the neg side of the coil

Please explain the coil picture again. Start with the white wire shown on the left. Where is it connected to? it looks like it is floating in space. Where does the old black braided wire go to?

You say the car is positive earth. The coil you have is a later type and should be wired accordingly.
(Positive earth coils were labeled SW and CB not + and -).
When you use a "new" coil on a positive earth car, the power to the coil from the ignition switch should be connected to the coil (-) terminal and the coil (+) terminal should be connected to the distributor. For more information see the link below.
http://www.guy.weath...com/ht/coil.htm
Specifically see the last line in the link "The primary terminal marked (-) must connect to the (-) terminal on the battery."
Therefore, on a positive earth car, you want that coil (+) terminal connected to the terminal on the distributor. However, let's return to your tach.

Go back to the SpeedyCables link I provided earlier. http://www.speedycab...page34aaaa.html
Your power connections to the tachometer terminal strip appear correct. The sense wiring (white wires) does not appear to be correct. Make the following changes.
THIS IS FOR POSITIVE EARTH ONLY.
Power FROM the ignition switch connects to the coil (-) terminal. No other wires go that coil terminal.
On the coil (+) terminal connect ONE of the two white wires.
Connect the other white wire to the distributor.
(Ignition switch power to coil (-), tach white wire on coil (+), the other tach white wire on the distributor. Only ONE white wire is connected to the coil.)

That's all you need to do. If the tach reads oddly, swap the connection points of the two white wires (move the dizzy wire to coil (+) and the coil (+) wire to the dizzy).

[mesrine]

thanks for your detailed response Doug. I have took on board all you have said.

firstly I was using the -neg side of the coil (lucas sport DLB 105) to link my pulse wire in. This was incorrect by all accounts.

So I re-made all the connections, and inserted the pulse wire in-between the +poss coil terminal. (Going by the "smiths fitting instructions)........red marker to the coil, black marker to the distributor.........(NOTE, speedy cables diagram link, says the exact opposite of this )

anyway, same result.....2200 rpm tickover........3500 rpm 30 mph, flat road steady revs..........4500 rpm 40 mph flat road steady revs.......and whan accelerating in any gear, its almost maxing round the clock

I then reversed the leads, black to the coil, and red to the distrib.....and exact same results....

I am now at a loss, tried every configuration going, with the same results.............

the cars battery positive terminal, is earthed to the car.


I paid a lot for an original unused smiths tacho KP 1250/00

i cant imagine anything could be wrong with it

regds ray

[mk3 Cooper S]

Sounds like an 8 cylinder tacho to me.

[dklawson]

Thanks for confirming the wiring. It sounds like your tach is wired correctly which calls the tach calibration and general gauge condition into question.

I wish I could give you further advice on this but you may in fact be dealing with problems internal to the gauge.

I went back and re-read some of the posts on the first page of this thread. One question does not appear to have been addressed so it must be asked now. Tiger asked you about the points and condenser in your ignition system. I did not see a response from you confirming that you are still using points. You haven't perhaps fit a positive earth electronic ignition have you?

[mesrine]

Yes the car uses points, its mostly original parts, apart from sympathetic upgrades like the coil. Thanks for your input and help.....I genuinely think I have it wired in correctly now (and I have had the time to try all the options), So perhaps on this occasion the r counter is reading wrong. Now to see if I can get it checked, or agree a return with the seller.

cheers Ray

[dklawson]

I'm sorry it doesn't appear to be working out. In defense of the tach (or partial explanation of its behavior) it is likely to be 40+ years old. The RVI series tachs were pretty much phased out by the mid 1970s. Even if this tach is new-old-stock, there may be things inside like dried up electrolytic capacitors that need replacing.

[mesrine]

Hi had the car on a rolling road today, gen consensus is tacho ok, wiring and fitting ok, but it needs calibrating,

anyone had experience of this ?

[dklawson]

t needs calibrating,
anyone had experience of this ?

Yes. However, it is not something easily done by most people at home. As I mentioned earlier the tach is measuring an inductive pulse from the current passing through the coil. I may not have mentioned it in this thread (but certainly have in others) that the duration of the current pulse (dwell) is important for these tachs to work properly.

I tried several circuits to create a 4 Amp pulsed current to calibrate the RVI tachs. While I could make the tachs work they clearly were not even close to working properly. Certainly not properly enough to calibrate.

I finally bought a spare distributor and built an ignition system on a board. I mount the distributor in the chuck of a DC drive powered lathe and use the board mounted ignition system to provide the current pulses through the tach. That works. However, to do this at home you would need access to a lathe with very good speed regulation and a tachometer to confirm the spindle speed. Again, it works but for most people it is much more effort than simply sending the gauge to a professional for recalibration.

[mesrine]

Thanks for that Doug, I have some friends in industry, now I know which direction I'm going in, I might be able to move forward on this.....what a sage over something I didn't really need in the first place.............