I changed the head gasket over the weekend (to get rid of my persistent "oil in the water but no water in the oil" problem). It all turned out to be fine but now with no other changes made the tacho is behaving irrationaly. It peaks at atleast 4000 on idle (the car is at 1000 rpm max) and responds agressively (by jumping up) to any electrics (such as lights, stereo, wipers) being turned on. When reving the car up on the road the tacho picks up when the revs match with the approx 4500rpm reading and rises with the actual revs but wouldnt exceed the usual redline. All other things being the same as before and having not touched the coil, tacho or any electrics for that matter when replacing the head what could it be thats sending the tacho up? (a short drawing current before the fuse box maybe?)

Also Kev whats the best way to get the most accurate rocker clearances with the pulsar dizzy. Usualy I'd double check the gaps by turning the wheel in 4th - having both valves closed and the plug sparking. But with the elec. dizzy I cant seem to be able to get the spark just by turning the crank over.

Cheers.

Usual cause of tacho jumping is a loose wire connection onto the coil.

Best way to adjust the valves is forget the spark- why would you want it anyway??

Use the so-called `rule of 9' to adjust them-
Look at the 8 rockers- number 1 to 8 from the fan end.
Adjust #1 when #8 is down, #2 when #7 is down, #3 when #6 is down. Get it? Adds up to 9...
Another way to look at this is mentally divide the engine down the middle between #2 & #3 cylinders, and work symettrically each way.

This all works because the valve events on say #4 cylinder happen 360* after #1 cylinder. This means that if #8 valve is fully lifted #1 valve is right on the back of the cam's base circle, the best place to adjust it.

In practice I get one inlet and one exhaust valve near fully open together, and adjust the 2 corresponding ones (using rule above) at the same time.

Turning the motor over as you do is OK, these days I just put it in 4th gear and pull the car forward. Saves getting the jack out.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

What brand of tacho is it that you are using. There is only 3 wires that can cause an issue really, black-earth, red-acc 12v, green- neg side of the coil. That is the general colour code on most aftermarket tachos. White is used for the lights. Does the tacho have a cylinder number switch on the back, as in 4,6,8 cylinder? Dr Mini is right with the rocker adjustment, otherwise just grab a gregorys service manual its all explained in there.

No no probs with the clearance adjustment, I use the 9 rule too when setting the clearances but since every single mechanic who ever looked at my clearances found that some of my settings are a bit off I started using the spark method just to double check that they are right (coz isnt all we realy ensuring by setting correct clearances is that the gap is right when both valves are closed and the plug sparcs?)

The tacho is a Veglia so probably from a Fiat, its there from the previous owner and I never got around to figuring it out. What puzzles me is that it is behaving as if it had its polarities reversed, and is also reacting to other electrics being turned on.

Well the wires to the coil are fine, and really it only jumps when i use any of the electrics - so with the engine idling but no electrical devices on the tacho needle goes down almoust to normal idle reading, with the brake pedal pressed the needle jumps to 2k (prob because of the brake lights) with the headlights on its on 3k, wipers and its 4.5k, stereo and its 5k etc. It still peaks at the normal rev limit (ie even being at 4k at idle it still wouldnt exceed the redline even at very high engine revs.

Any ideas of specialist auto electrical forums out there?