My 72 dart 225 slant 6 idles perfect but while driving stalls or wants to stall. It also backfires a little through the carb. accelerator pump seems to be working fine the choke flap is stuck open could this cause any of this. I figured i had a vaccum leak some where but cant find any is there anything else im over looking thanks

I can think of lots of things that could make this happen.

1. too low of initial timing.
2. vacuum can blown and leaking vacuum
3. sloppy timing chain
4. off a tooth on the distributor
5. top plate not phased correctly
6. water condensation in the distributor cap
7. broken or bad spark plug wires
8. bad condensor, rotor, cap or points.....
9. points not set right
10. if running a 73 and up distributor, bad pick up in the distributor.
11. etc.....there is probably many more items that when put under load would act like a vacuum leak....

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Aggressive Ted

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74 Swinger, 9.5 comp 254/.435 lift cam, 904, ram air, electric fans, 2.5" HP2 & FM70 ex, 1920 Holley#56jet, 2.76 8 3/4 Sure-Grip, 26" tires, 25+MPG

Sounds like your distributor is too far retarded. When you set the initial timing, make sure that the vacuum hose to it is disconnected, or you will have that issue. I learned this the hard way.

Basically what happens is:

At idle, the throttle plates are open far enough to pull vacuum on the distributor. This in turn bumps up the timing, and when you set the initial timing with the vacuum hooked up and pulling timing out, you get an inflated reading. So your timing may say 10 btdc, but that is inflated, and in reality you are running maybe 5 atdc.

So, when you step on the gas and vacuum drops due to the throttle plates opening, you lose the timing given to you by the vacuum which causes exactly the issue you describe.

Try plugging the distributor end of the vacuum hose with a screw or bolt, start the car, and then set initial timing to say, 5 btdc. Then adjust the idle screw so that you are idling at about 800 rpm, then set your idle mix screw so that the engine idles smoothest, and read adjust idle speed if needed to about 800 rpm.

If you have a vacuum gauge, use it to set your idle mixture screw. Basically, adjust the screw in until the idle starts to get crummy, and then adjust out slowly, watching the vacuum gauge until it doesn't go any higher. At 800 rpm, you "should" be seeing about 21" HG, or 21 inches of vacuum. At this point, blip the throttle a bit to make sure that the idle mix you have set will stay the same.

After that, hook up your vacuum to the distributor again. If your engine idle changes, you may have vacuum plugged into the wrong port on the Carb.

Let us know what you find out.

~RDE~

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1984 D100 Shorty Custom
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