Tach problems

[valkyrie 2]

I have a 1967 MGBGT. My tachometer seems to double the engine revs. The engine has a different coil and a mallory dual point dizzy. The tach input comes off the coil. Could one or either be the problem and any idea how to resolve. Also if I went back to a standard dizzy and used electronic ignition, I have heard you need to change the springs to stronger ones in the distributor. Any thoughts?

[woofhaven]

Not really an answer, but why fuss with the dual point distributor? And why go back to the standard distributor if you were going to switch to electronic ignition? I would think you would want to use the Mallory distributor and electronic ignition.

[valkyrie 2]

Originally Posted by valkyrie 2

I have a 1967 MGBGT. My tachometer seems to double the engine revs. The engine has a different coil and a mallory dual point dizzy. The tach input comes off the coil. Could one or either be the problem and any idea how to resolve. Also if I went back to a standard dizzy and used electronic ignition, I have heard you need to change the springs to stronger ones in the distributor. Any thoughts?

Point taken. My main concern is still getting my tach working. Right now the dual points are working unless this is my tach problem....Thanks

[Flash75]

Your tach is current operated so two set of points should cause it to read high. Disconnect or disable the secondary points to see if that is the cause. Four cylinder engines don't need dual points.

There is no need to change distributor springs when changing to electronic ignition. Points do cause a slight drag on the cam but I doubt that there is enough difference to notice.

Clifton

[valkyrie 2]

Originally Posted by Flash75

Your tach is current operated so two set of points should cause it to read high. Disconnect or disable the secondary points to see if that is the cause. Four cylinder engines don't need dual points.

There is no need to change distributor springs when changing to electronic ignition. Points do cause a slight drag on the cam but I doubt that there is enough difference to notice.

Clifton

Thanks for the reply. I put a small piece of cardboard between the secondary points and the tach still is doubling the revs. Any other ideas?

[Flash75]

I thought it may help. Do you have a stock coil you can try? It's just a guess but if you have the coil it's easy to try.

Clifton

[valkyrie 2]

Originally Posted by valkyrie 2

Thanks for the reply. I put a small piece of cardboard between the secondary points and the tach still is doubling the revs. Any other ideas?

Thanks for the reply. No I don't. But I do need to take her into a local shop for another persistant problem and I was going to ask if they could try one. I'll let you know if it works. I really think this could be part of the problem. Cheers

[KimMG]

What is the other persistant problem?

[1972MGB]

valkyrie 2,
I do not know if any one is still checking this thread, but I was having a problem with my tach reading about 1000 RPM to high when I was in the higher RPM range. My car is a 1972 and has the electronic tach. After doing some calculations of engine RPM, transmission gear ratios, final drive gear ratio and tire size I knew my tach was off. Anyway, the electric tachs are adjustable, there is a potentiometer in them that adjust how the tach reads. This is done by pulling your tach from the dash with it still plugged in, then there is a cutout on the back of the case and a place for a small screw diver. Mine has a yellowish looking screw inside this hole, turn this clockwise or counter closkwise to adjust how your tach is reading. I found this by looking at a wiring diagram of a tach, it shows this pot in the diagram. I would recomend seeting your tach against another aftermarket tach as opposed to setting against the speed of the car becuase if your tire size is different from stock, then your MPH to RPM ratio will be different than stock, it will get you close thouhg. Also, a hand held tach would work as well if you have one, or know someone that has one. Hope that this helps. One more thing, if your tires are stock (about 24.19in. in diamter) you should be doing 60 at about 3250 RPM. I can send you an excell spreadsheet that shows RPMs at different speeds if you are interested.

[valkyrie 2]

Originally Posted by KimMG

What is the other persistant problem?

Wow! What an answer. I would like your spreadsheet if possible. [email protected]. I will pull the tach out and give it a try. Thanks