rough running....backfiring 350

I wanna see how the distributor weights look like

All the other fellows suggestions are GREAT. Yes you do need vacuum advance on your HEI. It really does sound like a vacuum leak somewhere. Check ALL your vacuum lines for cracks/leaks. Get a vacuum gauge and a timing light. This link will explain that. (

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Also, did you remove the distributor? Because if you did, it COULD be 180 out and that causes those symptoms. Start with the basics as the other guys have said. Firing order. 1-8-4-3-6-5-7-2. Odd numbers are on the drivers side from front to back of engine (1-3-5-7) - even numbers are on the passenger side of the engine from front to back on engine (2-4-6-8). Replace cap and rotor if it's old. Check all spark plug wires for cracks. Confirm all vacuum lines are connected the way they are supposed to be from the factory. Take your time. Use you tube if you have questions - it's really helpful and will walk you through it. These old trucks are quite easy to work on if you take your time. Check timing as well with vacuum disconnected at distributor (plug it). Base timing should be around 8-10 BTDC (before top dead center) and all in should be around 35 degrees. There should be a tag on the core support showing you the timing for your engine. Depending on the engine mileage and shape - the harmonic balancer rubber insulator may have slipped a bit - (quite common) but this video will explain how to work around that.
See here:

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And make sure the gas is fresh. Also, check the throttle shaft on the Quadrajet for play (a common issue on Quadrajets). It is common for the bushings to wear on the Quadrajet, and that will cause uneven idle. See here:

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One step at a time, and write a log of what changes what. It will really help you. I know that's a lot.....but it is easy if you go ONE STEP AT A TIME, and note the changes in your journal. IF your Quadrajet is beyond hope - go with an Edelbrock 600-650 Carburetor with electric choke. Hope this helps !

Ken B said:

So here is my issue....my truck which has a 350 runs good if the trans is in park....rev it up and it runs good. Put it in gear and try and drive and it coughs and backfires and shimmy and shakes...any ideas??

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You've received a whole bunch of great advice in this thread. The only thing I would add is, even if you cure the problem beforehand, replace the distributor cap, the rotor, and the electronic module anyway, just because. It's just good preventive maintenance, and will keep you out of trouble down the road. Also make sure the advance plates in the distributor are clean and moving properly. (That's after you do what everybody else recommended.)

As a general rule for old vehicles, if it's flexible or conducts electricity, budget for its eventual replacement. And the more ordered and methodical you are, the better results you'll get.

AuroraGirl said:

I wanna see how the distributor weights look like

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AuroraGirl said:

I wanna see how the distributor weights look like

Click to expand...

Ya, since the port was plugged and dist may have been messed with or curved, colored tension springs may be seen too.

I have received lots of great knowledge and advice and I appreciate it all.
Back to work so will be a few days til I can see if I can diagnose or come back for more knowledge from the Forum

Progress update.
I got a timing light and checked timing it was way off. I set it about 10 before TDC backed out of the garage and accidentally left a tire mark on my driveway!
Went for a couple mile drive and the backfire is gone runs soooo much better. There is more to do but at least it is very driveable.
To EVERYONE who threw out ideas, advice and shared your vast knowledge I say,
THANK YOU SO VERY MUCH.
Be back later going for a drive!!!!!

Rainy morning,,, so maybe some garage time....
After a nice stress free drive yesterday I am researching why the secondaries arent opening on the quadrajet....stood on the throttle and no indication the carb is opening the secondaries.
watched a couple of videos on how the secondaries are supposed to open. will head out to the garage and start scratching my head and looking around in a bit.

Ken B said:

Rainy morning,,, so maybe some garage time....
After a nice stress free drive yesterday I am researching why the secondaries arent opening on the quadrajet....stood on the throttle and no indication the carb is opening the secondaries.
watched a couple of videos on how the secondaries are supposed to open. will head out to the garage and start scratching my head and looking around in a bit.

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They are demand operated,you probably will never get them open in neutral. The engine has to have a need for enough air to overcome the spring that holds them closed.

I was driving yesterday and stood on the throttle and no impact like the secondaries were open or trying to.
Sorry if i made it seem like i was just in the garage.

Good reading:

Ken B said:

I was driving yesterday and stood on the throttle and no impact like the secondaries were open or trying to.
Sorry if i made it seem like i was just in the garage.

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Make sure the truck is fully warmed up,the choke is fully open. If it still won't open the secondaries see if the secondary lockout is stuck,then I'd start playing with air door tension.