Carb question

[Lunatic]

If I had an original electronic quadrajet and have since replaced it with a non-electronic quadrajet, would that effect the running timing advance due to missing signals from all the electronics no longer present ?

If so, would a MSD ignition 6AL control resolve the issue ?

My 86 350 idles stupid sometimes, all the way to stalling. The only major change since last smooth running is the basic carb from SMI.

My idea is that because the computer isnt getting a "what to do" signal from the 2 gizmos on the old carb, it just decides to run safe mode rich by tweaking the advance at times, causing the engine to stumble.

Any possible truth in the above idea and solution ?

I'm still learning about carbs, so any useful information only helps.


Thanks !




Troy B
Ft Hood, TX

 

[badmix]

I have an '84 that had the quadrajet carb, I yanked it for a Holley 570cfm and I had to put a Mallory Distributor because of the problems you mentioned. And havent had any issues.

 

[76zimmer]

I believe the timing is controlled by EST, which can retard the timing under knock conditions. My 85 had a malfuncitoning EST computer and would retard the timing by 20* (verified w/ a timing light) I unplugged the distributor 4 way plug and jumped a wire across two of the terminals, in effect bypassing the computer. I would think an MSD would accomplish the same thing.

 

[Lunatic]

Thanks for the info badmix, 76zimmer.

The condition of all the components separately is not the issue, but the separate components not playing nice together seems to be causing the problem.

The carb, ignition module and coil are less than a month old, plugs are in good shape, and basically - In the last month - I have torn through the ignition system.

At this point, the carb is tuned and everything else is in order. 4* advanced, 18psi vac, needles 1.5-75 out, smooth curb idle. A previous hesitation and stalling issue was determined to be numerous misses and ignition problems (Thread found here). That issue is now fixed.

All that's left is this idle, stumble, stall issue.

In the beginning, I had to drive around the neighborhood to diagnose and test drive. The issue only existed while feathering the throttle to stay at speed (25mph). The engine would suddenly loose power and try to stall. Giving more throttle would clear the situation. With black soot for plugs and exhaust rooster tails on my driveway - That says rich. Adjustments made included needles, electric choke, dist cap, ign module, coil, and new plugs.

That's where this thread picks up. I had only wanted the idea of possible solutions to be addressed (in a vague fashion) but now realize all the information available will be needed to get the most accurate knowledge for a solution.

Last weekend, I made some final tweaks - Nothing major - And took the truck out for about 40 miles in one day, two separate trips in two separate directions with no problems other than a lacking power band in OD (Something I'll address once this is figured out). But on the final road home, the truck actually lurched hard, which made me cut to the slowest lane. Once in D it didn't return. I still have no ideas about what made that occur.

Here's two examples of most recent experiences.

• Monday morning - Sat at a red light for about 35-40 minutes (There is a justified reason, really). At that time (40min), still in OD/D, the engine stumbled and tried to stall. I killed the engine - I wasn't going anywhere at that time anyways. But it did show up in OD/D, sitting still, after 35-40 minutes.

• Monday evening - Barely out of the parking lot and the stumble / stall popped up again - all the way home (15 minute drive).

The truck has been parked since due to rain. I'll check anything if I'm pointed in that direction - I'm not embarrassed to admit I'm learning the carb (and that I want to learn the carb.). I've tried everything I knew to check and then some. Now I'm in the 101. So school me if you like - I'd appreciate it, sincerely.

......And I will be picking up some NGK V-Power #2771 plugs as soon as the rain clears to get the Bosch plats out of the equation.




Troy B
Ft Hood, TX

 

[K85 Octane]

I had the CCC and HEI on my CA '85 blazer.

I bought a late 70s Q-jet and MSD pro billet distributor. I pulled the computer out and tossed everything I could. I had to save some of the emission connectors and dummy wire it into my new wiring harnesses. If you don't have to deal with smog, you wont have to worry about this step.

Everything plays together perfect. Also, you should run more timing. ~8-10* I currently run 15* but it's not a stock engine.