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coil/distributor wiring - Exciting new details!

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coil/distributor wiring - Exciting new details! #1
chanson C Hanson South Florida, FL, USA Sign in to contact 1973 MG MGB	Topic Creator (OP) Dec 18, 2014 07:23 AM Joined 15 years ago 1,855 Posts

Most of the time I'm able to find answers to asked and re-asked question, but not this one. I assume I'm looking in the wrong place. At any rate...

I'm putting in a new distributor fitted with Petronix. All wiring is original, and hooking up red to positive and black too negative on the coil is an obvious no-brainer. But I'm wondering what I do with the Black/white and white leads originally fitted to the coil. Looking at the wiring diagram, I am under the assumption that I leave them connected as well, though making sure I insulate the former distributor negative lead on the distributor end so as to avoid shorting/grounding. (original wiring harness has distributor and tach coming off of the negative in one single female connector from the coil end. I'd rather not cut into the harness if I can avoid this).

Does this sound correct?

Edited 1 time(s). Last edit at 2014-12-18 09:05 AM by chanson.

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Re: coil/distributor wiring with Electronic ignition. #2
Donthuis Don van Riet Rijswijk, ZH, Netherlands Sign in to contact 1972 MG MGB MkIII	Dec 18, 2014 08:04 AM Top Contributor Joined 10 years ago 13,336 Posts

If your (late?) 1973 B has the voltage sensing tacho inside, this stands not in series between + battery and + coil, so I guess you connecting the Petronix to + coil is OK. If not it should be attached to a switched + battery connection instead or the RVI tacho may not work. Another sign could be this black and white wire to the coil: for voltage sensing tacho's this is the sensing connection to - coil and should therfore be retained. White lead I'm not sure about, is it not the connection between - coil and the old distributor? At least that's the configuration on my own (early) 1972 B .

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Re: coil/distributor wiring with Electronic ignition. #3
chanson C Hanson South Florida, FL, USA Sign in to contact 1973 MG MGB	Topic Creator (OP) Dec 18, 2014 08:22 AM Joined 15 years ago 1,855 Posts

I'm not sure whether my tach is voltage sensing.

In reply to # 2875280 by Donthuis Another sign could be this black and white wire to the coil: for voltage sensing tacho's this is the sensing connection to - coil and should therfore be retained. White lead I'm not sure about, is it not the connection between - coil and the old distributor? At least that's the configuration on my own (early) 1972 B .

I'm pretty sure that the (2x) black/white coming off the negative go to the distributor and to the tach. The white is wired to the third fuse down. At least that's how it appears in the wiring diagram. I suppose I could remove wiring sheathing to verify this. But I'd really rather not. I'm pretty sure my car is a late 73.

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Re: coil/distributor wiring - Further strangeness #4
chanson C Hanson South Florida, FL, USA Sign in to contact 1973 MG MGB	Topic Creator (OP) Dec 18, 2014 09:04 AM Joined 15 years ago 1,855 Posts

Thanks for the confirmation. I've got the car up and running with the new distributor.

What prompted this swap was poor gas mileage that I was unable to fix via timing, carb balancing and mixture. That, and the idle had a recurring "blip" in it. As I write this, it just occurred to me that I haven't set valve lash, so I'll need to go back and do that.

But here's the strange thing. I bought a colortune to use after I got the new distributor in. On number one it showed the "Bunsen blue" the manual suggests. On number four, however, it showed NOTHING at idle except when the aforementioned "blip" occurred in which there was a quick flash of color.

what gives?

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Re: coil/distributor wiring - Exciting new details! #5
Dick Steinkamp Bellingham, WA, USA Sign in to contact 1977 MG MGB V8 Conversion	Dec 18, 2014 09:21 AM Joined 14 years ago 907 Posts

I would guess that #4 isn't firing. Plug wires? Spark plugs? Wrong firing order? Valves adjusted too tight? Burned valve?

What do the other 2 cylinders look like on color tune?

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Re: coil/distributor wiring - Exciting new details! #6
ohlord Rob C A tiny Island off the coast of Washington State, N.W., USA Sign in to contact 1957 Land Rover Series I "EYEYIYI" 1957 Land Rover Series I "OVRLND" 1971 MG MGB 1971 MG MGB "Bedouin 2" & more	Dec 18, 2014 03:43 PM Top Contributor Joined 12 years ago 28,878 Posts

1342 CCW make sure all wires are seated,adjust valve lash properly,install new plug wires and coil wire ,pull off #4 and see if rpm drops noticeably. If not you might have a flat lobe or other issue with that cylinder.
Replaced plugs? NGK BP6ES .025 gap

LNDRVR4X4.COM
Home of Project "INCARN8'

1957 Series 1 Land Rover electric VEHICLE CONVERSION

FIXITUPCHAP.COM
FIXITUPCHAP INCORPORATED

RD3 Radar/ Electronic Warfare Technician
VIETNAM 1969-1972

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Re: coil/distributor wiring - Further strangeness #7
Donthuis Don van Riet Rijswijk, ZH, Netherlands Sign in to contact 1972 MG MGB MkIII	Dec 18, 2014 04:04 PM Top Contributor Joined 10 years ago 13,336 Posts

Colortunes tend to rather lean mixtures on the Bunsen blue color. I use two colortunes for easier mixture comparison between both carbs and after tuning both on blue then enrich again by 1 or 2 flats. 1 flat equals a quarter turn on HIF's and a sixth turn on HS

PS You've got the wiring correct, since tour late 1973 tacho is voltage sensing

In reply to # 2875322 by chanson Thanks for the confirmation. I've got the car up and running with the new distributor.

What prompted this swap was poor gas mileage that I was unable to fix via timing, carb balancing and mixture. That, and the idle had a recurring "blip" in it. As I write this, it just occurred to me that I haven't set valve lash, so I'll need to go back and do that.

But here's the strange thing. I bought a colortune to use after I got the new distributor in. On number one it showed the "Bunsen blue" the manual suggests. On number four, however, it showed NOTHING at idle except when the aforementioned "blip" occurred in which there was a quick flash of color.

what gives?

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