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Re: Tach pegs when cranking

To: Eddie Sheffield <>
Subject: Re: Tach pegs when cranking
From: Stuart MacMillan <>
Date: Wed, 13 Jun 2001 14:44:35 -0700
I've got a Pertronix ignition, so it has nothing to do with points or
condensers. I'm going to examine the circuit diagram tonight for clues. 
It looks  like it is  getting a full 12v from somewhere until the engine
starts.  It certainly could be an internal problem, I may swap out the
tach and check that.

Eddie Sheffield wrote:
> I'm anxious to see if there are any hints on this. My '71 Midget does a
> similar thing, though not consistently. Never noticed any connection to any
> other circuit though (like your wiper problem). But sometimes it pegs just
> turning on the switch, usually accompanied by a high-pitched squeal. I'm
> guessing that the points happen to be in a closed position, so perhaps the
> constant current flow is being seen as "infinite" RPM. A couple of times
> when this has happened the tach would read around 3K too high - I'm guessing
> some capacitor in the tach picked up a full charge and was sort of "biasing"
> it. Another time it didn't work at all after starting. Most of the time it
> seems fine though. Kind of strange.
> I've been surprised that my tach works anyway. It didn't when I got the car,
> so I opened it up and discovered a transistor that hadn't been properly
> soldered to the circuit board and one lead had come loose. Resoldered it and
> it pegged the needle first try, but after that worked nicely - was even very
> close to being properly calibrated. So whenever it works, I'm happy. ;-)
> Eddie
> 1971 Midget

Stuart MacMillan

'84 Vanagon Westfalia w/2.1
'65 MGB (Daily driver since 1969)
'74 MGB GT (Restoring sloooowly)

Personal mechanic for:
'70 MGB GT (Daughter's)

Assisting on Restoration (and spending OPM):
'72 MGB GT (Was daughter's, now son's)
'64 MGB (Son's)

Stripped and gone but their parts live on:
'68 MGB, '73 MGB, '67 MGB GT

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