The Webmaster Zone

I bought an inductive timing light and a combined tach/dwell meter today, both Sunpro units. I had set the timing statically in September but had overheating problems which I fixed by rotating the dizzy around until the car ran well. I knew the timing was off, but I didn't know how much. I read the instructions and figured out what went where taking into account the fact that my '66 is positive ground; very simple to hook up. First I connected the tach/dwell meter to check my tachometer. I knew it was wrong and I was itching to prove it. Back in October I calculated the engine r.p.m. for a given speed and gear, by multiplying engine speed, transmission ratio (4th no O/D is 1:1), rear axle ratio, and tire circumference to give m.p.h.. I got almost exactly what can be found in the Special Tuning Manual: 17.6 MPH/1000 RPM in 4th gear, no OD. My speedometer is (correctly?) calibrated to k.p.h., courtesy of the PO, so I didn't trust that either. Going down the I5 I realized that if I timed it so that I was taking exactly 60 seconds between mile markers, I would be going 60 m.p.h., which would tell me if the gauges were correct. The speedometer is close to correct; but it's still the wrong speedometer for my transmission as I've talked about before. The tachometer was way off, reading about 4,500 r.p.m. when, by my calculations, it should read 3,400. I could have had a helper twist the potentiometer in the tach while I did a timed 60 second mile, but I wanted to calibrate the tachometer either out of the car electronically or by a meter hooked up to the ignition system, out of paranoia more than anything else. Well it turns out the tach is wrong, which should come as no suprise. I pulled it out of the dash (remove the two thumbscrews in the back and the supports under them, remove indicator stalk cowl and slacken and rotate stalk for clearance, pull tach out the front) to get started on that. There is a small potentiometer inside than can be rotated to adjust the display. I have seen advice to drill a small hole in the case to aid in adjustment without the need to remove the case. Tomorrow's job; instead I turned the meter to measure dwell after rocking the car and setting the points gap to 0.015". I was suprised to see it only reading about 30 deg, my Haynes manual lists the dwell as 60 deg. I pulled off the cap and made the gap smaller by eye. After several iterations I got the dwell angle to 60 deg; but now the points gap was very small, much smaller than 0.015". Interesting that the first time I set the timing I found the gap to be quite small; now I'm not sure if my method is wrong or there is something wrong with the points or another component. Regardless, its set to 60 degrees now. I hooked up the timing light and slid under the front of the car to find the timing marks. Armed with a bit of Liquid Paper I tipped the end of the three timing marks (TDC, and 5 and 10 BTDC) and touched up the mark on the pulley wheel. Fired up the gun and whats this? The car is running extremely advanced, about 20 degrees. Possibly changing to the correct dwell made it worse. I slacked the adjustment bolt on the dizzy and rotate it far clockwise. Improved, its almost TDC now, but not far enough. Recheck the dwell and now its huge! Reset to 60 degrees. Check the timing, reducing the dwell has advanced it more. I fiddled around for a while longer, it seems like I have the dizzy turned as far as it can go clockwise, and the timing is still advanced from spec, so that will warrant some investigation. Packed up and went for a test drive. SWEET JESUS! I had no idea how bad it was; it still felt peppy and could match modern cars; but now it pulls like a TRACTOR. Watched the temp gauge carefully and listened for pinking, and all seems well so far, so I'm pretty pleased. I'll have to remember how it was in case I can't pass emissions next year. More to come tomorrow; its weekend MGB fever!