Incomplete HEI conversion...what to do

[Siedl]

Hi! I just picked up a 72 gmc stepside and from what I can tell they attempted to convert to an HEI ignition but didn't change the distributor, left the vacuum hose detached from the carb and hanging, unplugged and didn't change any of the spark plug wires.

The truck has started randomly dying, today going 40mph. My research tells me it could be timing or carburetor but wonder if it could be the unfinished conversion/possibly the vacuum hose that's just dangling there.

Any guidance is appreciated! Thanks in advance!

[hugger6933]

Welcome to the site, you need a HEI dist of course with cap and wires then you need a hot with IGN on a 12 volt source most run a wire from the fuse box. Then you need to plug up that vac hose that is just hanging out off of the vac source. Set the timing and then your pretty much ready to roll.

[Siedl]

Thanks so much for the step by step! Do you think this could be why the truck is randomly dying? I've had people tell me everything from carburetor to fuel pump to timing. Was going to try a new fuel pump first since it's the easiest but don't think that's really the issue...

Also, should I plug the carburetor where the vacuum hose went or just plug the hose coming off the distributor? Sounds likes silly question but I'm still getting through the learning curve!

Thanks so much! My mechanic partner bailed and left me without his expertise so this forum has been a great support!

[68350]

The carb side is the vacuum you need to plug. But if the distributor is set up for vacuum advance you should hook the hose up

[COBob'70 K-10]

Just a suggestion:
While you can run the hot wire to the fuse panel, I ran mine to a toggle switch. Now, no matter how long the engine is cranked, until the switch is on, no ignition.
Call it a cheap bit of security.

[Davidf]

I wanted to free up the "ignition on" spade terminal in my fuse box, so I order a new engine wiring harness for HEI from Classic Parts. All the conversion wiring is integrated into the new harness and looks totally factory. Well worth the $100 or so. Plus it was an easy way to clean up all the hacked up existing engine wiring. If you go this route, don't forget to order a new wiring junction block gasket.

[Siedl]

Thank you guys so much for your replies. I'll let you know how it goes.

[dirtyjim]

m&h sells the hei lead for around $6 with the hei terminal on one end and Packard 56 terminal on the other. cant build one for that price. they are also sold through oc truck shop.

[leftybass209]

Originally Posted by dirtyjim

m&h sells the hei lead for around $6 with the hei terminal on one end and Packard 56 terminal on the other. cant build one for that price. they are also sold through oc truck shop.

Definitely can't build it for that! I know because I did. I don't like splicing so I have an HEI harness from m&h, and a modified alternator/headlight harness so everything looks factory, no extra wires, and no chance of a short due to negligent splicing.

Sorry I got off track. I would start by looking at a schematic here for HEI. Take your time, trace your wires, and make sure it's all correct. Then of course, by an HEI distributor!

[michael bustamante]

quick question though. if you have a good oem harness and its still very useable, what can you do with the two yellow wires that used to be on the oem coil? maybe for the electric choke?

[bronze 72 super]

Yes, as long as the power source is off when the ignition is turned off, and key off. Did this on my '70 El Camino with a holley with electric chock. No problems.

[michael bustamante]

Cool thank you