The problem you are referring to with you XR700 may have to do with
"phasing" of the shutter and infrared unit in relation to the rotor arm
position. I read about this last night in the most recent Grassroots
Motorsports magazine. They did a comparison of a Pertronix, a Crane
unit, and some other setups on a carburated Volvo with a dizzy that has
mechanical points as the stock setup. They mentioned something about
making sure that the rotor arm is positioned in just the write place
(directly below the #1 pickup on the dizzy cap) when setting the static
timing using a Crane unit. Crane apparently recommends using an old
dizzy cap with a hole cut in the #1 pickup location to get everything
just right. I'm still trying to understand all the details, but maybe
this is the problem you are having. Theoretically, if your phasing is
off, the Crane unit could be triggering the coil to fire when the rotor
is a bit far from #1 pickup. Not a big deal at idle, but it could get
worse at higher engine speeds as mechanical advance builds. At that
point, perhaps the rotor arm could be far enough away from #1 on the
distributor cap that it causes a misfire. Then again, I could be
completely wrong here. I still can't figure out exactly what
Grassroots was getting at....
Tim Holbrook
1971 TR6
--- Gameparker@cs.com wrote:
> From: Gameparker@cs.com
> Date: Mon, 17 Jun 2002 20:50:40 EDT
> Subject: Re: Upgraded plug wires & ?s re Distributor Advance & Timing
> To: Bruce.Simms@SOCO.Sk.Ca
> CC: 6pack@autox.team.net
>
> Bruce,
> I'd like to share with you something that happened to me two weeks
> ago. I am
> running exactly the same set-up as you - fast-road cam, headers, twin
> SU's,
> higher compression head, etc. I was also running the Petronix
> electronic
> ignition which started to go bad two weeks ago. I initially put the
> points
> back in and the car ran quite well. I also have a spare XR700 system
> which I
> decided I would go ahead and install (only took a few minutes because
> I just
> velcroed down the gold "box"). Initially, I thought it was running
> quite
> well with just some high rpm pinging. Turns out, that in order to
> get rid of
> the pinging, I had to retard the timing so much, that I had turned
> into the
> proverbial garden slug! It was a good thing that I was retarding the
> timing
> by taking off the cap and rotating the optical sensor clockwise,
> instead of
> rotating the actual distributor, because I just took out the XR700
> and
> dropped the points back in and everything was good again. So, the
> quandary I
> was in was that: I didn't want to go back to Petronix, I didn't like
> the way
> the XR700 made me perform, and the points just didn't have the high
> rpm
> performance I needed. Someone on the list suggested looking in to
> the MSD 6A
> unit, which utilizes the existing points (which last a long, long
> time with
> this system) and has all the other benefits of elec. ignition. Mine
> is
> coming tomorrow- I'll let you know how it performs.
> Regards
> Geoff Parker
> 74 TR6
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