[Clayton Ketchum]

Hi,

I recently acquired a new OLD truck (1986 Chevy K10) with a custom engine that i don't know a lot about. Currently I'm trying to figure out what this vacuum line is doing (see pic attached). any help is appreciated!

thanks

 

[Clayton Ketchum]

Also the little that i do know about the engine is as follows:
Carb: Edelbrock 1406 electric choke
Engine casting #: 3970010
Engine ID: V0207TJB
Don't have partial VIN yet, still looking
I've been told it has a big cam in it also.

 

[RWENUTS]

Hi,

I recently acquired a new OLD truck (1986 Chevy K10) with a custom engine that i don't know a lot about. Currently I'm trying to figure out what this vacuum line is doing (see pic attached). any help is appreciated!

thanks

On my old 84 truck that was a switch for the lock up convertor. Do you have a 700R4 automatic tranny?

 

[RWENUTS]

Also the little that i do know about the engine is as follows:
Carb: Edelbrock 1406 electric choke
Engine casting #: 3970010
Engine ID: V0207TJB
Don't have partial VIN yet, still looking
I've been told it has a big cam in it also.

You got a 350 truck motor.
Suffix code TJB is found here.
Decoding small block Chevy engine suffix codes and stamped numbers TBT - TJS

 

[joe_padavano]

On my old 84 truck that was a switch for the lock up convertor.

^^^^THIS!

The TH350C and the 700R4 both used lockup converters that year, but since the truck did not use a computer for the engine, GM needed a stand-alone system for lockup control. In this case, the vacuum switch disengages the converter clutch at wide open throttle (low engine vacuum conditions) so that you can accelerate without lugging the engine.

 

[RWENUTS]

^^^^THIS!

The TH350C and the 700R4 both used lockup converters that year, but since the truck did not use a computer for the engine, GM needed a stand-alone system for lockup control. In this case, the vacuum switch disengages the converter clutch at wide open throttle (low engine vacuum conditions) so that you can accelerate without lugging the engine.

To add a little more, the vacuum was supplied thru a thermal vacuum switch. No vacuum to the switch on the firewall until the motor was warmed up. And that prevented it from going into lockup when the motor was cold.
I hope that's clear as mud!

 

[Clayton Ketchum]

Thanks for all of the quick responses!
So how should i hook up the vacuum advance to the hei distributor? Currently the vacum line from the carb to the clutch switch is for ported vacuum (left side of carb). There is another port on the right side that is full vacuum. Should i use both ports, or pick one and use a "T" to connect both the switch and the distributor?

Thanks!

 

[RWENUTS]

Use the manifold vac one for the vac pot. You might need to limit the vac advance if it pings.
Some info on doing that.
http://www.crankshaftcoalition.com/wiki/Hot_rodding_the_HEI_distributor

Where do you live and do you have more pics of your truck and motor?

 

[Clayton Ketchum]

I live in NE Ohio. So, just for my understanding, i should leave the lock up switch connected the way it is and run a second vacuum line to the distributor vacuum advace from the other full manifold vacuum port on the carb?

Also, here is a link to more pics of the truck and engine: https://goo.gl/photos/KkJyNd1LJzy4s5UJ6

 

[RWENUTS]

I'd unplug the line to the lock up switch until you find out which vacuum source your motor likes.
Try it on both.
What rpm does it idle at?
What's your initial timing?

A couple things for you to fix before they become catastrophies.
You need a metal tubing line for your fuel line. Rubber ones can leak and create towering infernos.
You need a double spring for your carb throttle. If one breaks you have a backup.

THanx for the pics!

 

[joe_padavano]

The lockup switch is unrelated to the distributor vacuum. Why unplug it at all? If the truck still has a trans with a lockup converter, you want that switch. There are lots of potential vacuum taps for the vac advance to get either manifold or ported.

 

[Clayton Ketchum]

Ok, so i did some poking around today under the hood, and i found some new information. the sensor on the cowl wall is called a "tip in" sensor and is part of the ESC (Electronic Spark Control) System. After tracing all of the wires i found that there is no Knock sensor, and the distributor is not compatible with this system either, its an MSD Street Fire 8362.

I have attached a wiring diagram of the ESC system and some pics of the unconnected wires.

Now I'm wondering if i can just do sway with the system all together and just use the current distributor with vacuum advance and be done.

Here is a link to more pics, it is updated as i take more too!
https://goo.gl/photos/KkJyNd1LJzy4s5UJ6

 

[RWENUTS]

Put it all in a box and use the ports on your carb to experiment with for what your motor likes.

 

[64nailhead]

That system is unneeded. Probably whomever put that motor together didn't know what it was so they left it there. You are correct, definitely not in use presently.

I have to say that I've gone junkyarding for that system and never found one that was in tact. You can setup that ESC module, with a knock sensor, to turn on a dash light when knock is detected - that is a quite handy tool to have when tuning. Especially if you have a loud exhaust which makes it demanding to audibly detect ping at high RPM's. The only items you would need are the correct knock sensor, a relay and/or dash LED.

Like the truck though.

Also, you could relocate the vacuum switch for the converter lockup into the cab so as to eliminate that under hood eye sore.