XR 700 Ignition Problems
Thread Starter
Melting Slicks
Joined: Dec 2015
Posts: 3,181
Likes: 732
From: Texas City, TX Texas
XR 700 Ignition Problems
I did my brakes and have put some miles on my '74 small block coupe. Rebuilt the engine, has only a fewhundred miles, haven't even properly tuned it up yet. Original(?)tach drive distributor, New cap, rotor, coil, wires, plugs. Old Alison points eliminator. Car was running fine, then quit, had it towed home on a Saturday night. Checked the next day, had spark from the coil, and the plug wire, but I didn't trust it so I ordered a new F.A.S.T. XR700. Installed it, now I only have spark from the coil, not the plug wire. Any ideas?
Thread Starter
Melting Slicks
Joined: Dec 2015
Posts: 3,181
Likes: 732
From: Texas City, TX Texas
Took it all apart and checked everything, looks good, cap, rotor, coil, wires, plugs all have less than a thousand miles. I have some sort of meter with two probes, not the kind with the big pincher on it. I am severely challenged when it comes to electrical.
Race Director
Joined: May 2006
Posts: 18,690
Likes: 2,572
How did you determine you have spark from the coil, did you disconnect the center wire from the cap and hold it near a metal engine part while cranking and see a spark jump?
how did you determine you have no spark at the plugs, did you disconnect a wire from a plug, insert a screwdriver into the wire boot and then hold the screwdriver near a metal engine part while cranking and not see a spark?
how did you determine you have no spark at the plugs, did you disconnect a wire from a plug, insert a screwdriver into the wire boot and then hold the screwdriver near a metal engine part while cranking and not see a spark?
Last edited by MelWff; Apr 23, 2021 at 10:36 AM.
Thread Starter
Melting Slicks
Joined: Dec 2015
Posts: 3,181
Likes: 732
From: Texas City, TX Texas
Yes and yes. A couple of my friends, who are more talented than me, determined that the optical trigger got damaged when another slightly less talented friend and myself installed it. We will be dropping in an HEI so I can make it to the show tomorrow. I hope it's just a simple swap, no special parts needed?
Melting Slicks
Joined: Dec 2009
Posts: 3,229
Likes: 656
From: Thunder Bay
In my limited experience those optical trigger ignition systems are notoriously unreliable and offer no advantage over an HEI. And yes, swapping in an HEI is about as simple as it gets, assuming you understand how to time the engine correctly.
Melting Slicks
Joined: Dec 2009
Posts: 3,229
Likes: 656
From: Thunder Bay
If you do decide to install an HEI remember to eliminate your ballast resistor. HEIs require a full 12 volts.
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Dr. Detroit
Joined: Mar 2012
Posts: 10,095
Likes: 4,025
From: New Braunfels Texas
Try to run a 12ga wire from the BAT on the HEI to the switched ign on your fuse box.......that 12v wire draws a lot of current and smaller wires heat up.......was classic in the 80's when all the Backyard Bill's started converting their crap to HEI.....leaving the 18ga wire to power it and having it melt.
You can buy premade HEI power plug w/wire.....makes for a clean install.
https://www.ebay.com/itm/10552-GM-HE...-/302474328573
Jebby
You can buy premade HEI power plug w/wire.....makes for a clean install.
https://www.ebay.com/itm/10552-GM-HE...-/302474328573
Jebby
Drifting
Joined: Mar 2006
Posts: 1,263
Likes: 188
From: Wabasha Mn
Yes if you have a cable driven tach its not going to work with a factory HEI. There are HEI distributors available with the tach drive. The other option is to convert your point style distributor with an electronic conversion setup, which is obviously what you were trying to do with the optical setup. Not a bad plan - just the optical setup can be problematic. I have used the Pertronix kit with good results. Or you can just stick with points. For all we drive these cars its not a bad option.
If you do decide to install an HEI remember to eliminate your ballast resistor. HEIs require a full 12 volts.
If you do decide to install an HEI remember to eliminate your ballast resistor. HEIs require a full 12 volts.
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,116
From: Crossville TN
You can go to Pertronix electronic ignition module installed in your original distributor and keep your tach drive system. If you have already purchased the HEI, you could resell it to someone as it is "new" and the net expense of going Pertronix would not be much of a loss.