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MG MGB Technical - Tach reads high after Pentronix Ignitor installation

Well, I just installed the Ignitor kit I got for Christmas and it works well, but now the tach is reading about 1500 rpm too high. I put it on my 71B that has a 25D diz and a Lucas Sports Coil.

It runs pretty smooth and was easy to install, but I'm going to switch back if there isn't an easy solution to the rpm problem. It is already making me nuts!

Anyone have any ideas?

Robert
Robert Rushing

Robert..Just a thought. When I installed a Crane XR700 system in my car, the tach would shoot way too high when revved over 3500/4000 rpm. In the instructions, Crane said if this happens, install a 10K 1/2 watt resistor in series with the lead going to the tach loop. This would cut down the voltage/current to the tach pickup but not to the ignition. For some more info, check out the Crane website, seems to me they also had some info on this there. This info may not apply to you but I thought you might like to know.
Steve
Steve Brooks

Robert. There is an adjustment/calibration screw on back of the tachometer. I would
try adjusting it first and see if that helps. Use a plastic adjusting tool if you can find
or make one. Crane suggests removing one loop of the current sensing loop to reduce
the current. The loop is inside the tach on the 71 and it isn't easy to remove a loop.
Crane suggest the resistor for the electronic tachs. Since your system is a pertronix it
would be a good idea to check with them before making changes inside the tach. The
last time I checked they had a website, but I don't have it bookmarked. Clifton
Clifton Gordon

Robert, put a dwell/tach. on the engine first to see just where your engine is idling at. Then you can make any adjustments to your vehicle tach. to bring it into play, if it is the tach.
victor gardino

Dear King Robert:

Changed over to Pertronix last year on my '69. No problems but there was a thread here at the same time informing us that unless the little gadget in the dizzy was well grounded, the result could be a funky tach.

Check the little ground wire inside the dizzy.

Good luck,

Luis
Luis

Thanks guys!

I'll check the ground first since that is the least intrusive, but will probably switch back to points before fiddling with the tach just to make sure that the Pentronix is the problem.

Robert
Robert Rushing

Robert,

in either case you will benefit from a good ground wire. That little stray wire that runs from the screw for the capacitor lead to the breaker plate mounting screw on the body of the dizzy is the one you need. Make sure it is in good repair as sometimes these get abused and fray all to hell, giving you only a lousy connection. If you have to replace it, replace with finely stranded wire like it, for flexibility.
Bob Muenchausen

This thread was discussed between 28/01/2002 and 01/02/2002

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