mis-reading rev counter

baggy_aggy · Post by **baggy_aggy** » Thu Nov 24, 2005 8:20 am

Took my 1970 911 T up to bedford on Sunday to give a dam good blast, part way up the A1 I noticed that the rev counter was not sitting at its usual 3000 rpm (I'm used to driving my karmann so 3000 rpm is a blast), in fact it was 'oscilating', for want of a better word, about 400 rpm above and below. Engine speed was constant. Also when I stopped to fill up the engine was definately idling about 850-900 rpm but the rev counter was reading 2000 (well twiching around that point).

Anyone out there seen this before, car runs fine, but seeing that I normally use that as reflection of speed (speedo hid of course), it is a bit off putting.

Cheers.

impmad2000 · Post by **impmad2000** » Thu Nov 24, 2005 8:34 am

From what I've seen on Pelican forum, bouncing tacho is usually associated with poor charging circuits, believe it or not ! Do you have a Voltmeter ? can you check what the battery voltage goes up to when revved ? should be about 14 and a bit Volts. If not, stays around 12V, then this bouncing tacho is early warning of a charge fault.
Don't forget that a 911 6 pot always sounds faster than a 4 (assuming 4 pot in the KG) as there are 50% more bangs per rev, but you already know that of course. You may be able to verify the tacho using a strobe with an RPM readout.
Cheers
Tim

bjmullan · Post by **bjmullan** » Thu Nov 24, 2005 9:12 am

Another thing to check is badly worn points (if you car has them!) I noticed that just before my point gave up the ghost the my tacho was all over the place just like you described.

baggy_aggy · Post by **baggy_aggy** » Thu Nov 24, 2005 9:24 am

Ok, still a bit new to this porsche thing, but with my KG i've replaced the points with an ignitor ignition set. MDR mentioned that there is a simlarly option for flat sixes (is it the MSD?). I've still got points in mine which I'd like to get rid of. I'm presuming that it is not a straight forward swap like the flat four?

Thanks for the info

Luke · Post by **Luke** » Thu Nov 24, 2005 9:26 am

check your timing and points its probably jsut them.

MdR · Post by **MdR** » Thu Nov 24, 2005 1:09 pm

Don't blame me

Lewis, I've got a (as yet unfitted) MSD which is not a points replacing gadget. I'd love to find a points replacing gadget a la Ignitor for the 911 but so far I have searched in vain....
Pelican parts list THIS stuff.

baggy_aggy · Post by **baggy_aggy** » Sat Nov 26, 2005 11:43 am

Thanks all, it was the points gap. Goes a tad better.