Running too rich-can’t figure it out

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Mako21

Mako21

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You guys must be sick of me. THe rare times I post, it’s the same issue. I can’t seem to fix it. Here’s my problem (again)
1976 Dart 225 all stock 904/2.73 rear

Idling too long or driving in D (3rd gear) typically 40 mph or less my car starts fouling plugs (starting with cylinder 1) and progresses to worsen fouling cylinders 2, 3 and so on.

My fix has been to:
1. Remove spark plugs every 50 miles, clean with brake cleaner, regap, reinstall. Short time fix.
2. Rebuilt the carburetor (H1945) completely. Also changed out plugs, rotor, wires.
3. At this point I pretty much have the idle mixture completely seated, out just a little and it’s helped a lot, but I’m worried of running her to lean. **If I seat the idle mixture screw all the way in, the engine continues to run. It does not shut off**
4. My latest solution is just drive everywhere in 2nd gear probably spinning 3000rpms around 40mph and this has solved all for now. I’m guessing it’s happy just burning all the extra fuel and not fouling plugs, but I do worry at these rpms danger of running too lean.

I know it’s running too rich, but I can’t seem to fix. As stated I rebuilt the carb, new floats, jets, needle /seat. Don’t know what I’m doing wrong.
Any other suggestions?
 
Any chance that you are dealing with a weak spark or a timing issue? IMO, idle mixture screws shouldn't effect low speed cruising.
 
Well, good point , I changed the ignition components, not sure how to check the spark resistance other that grounding the plug on the valve cover and seeing it spark.

Is there a procedure or write up for this? I imagine I’d need an electrical tool to diagnose this.

I just keep coming back to the carb and putting more time, effort and money into it.
 
I had a 440+6 in my 69 Barracuda that would foul the plugs. Of course I blamed the carbs. Turned out a junkyard ground strap fixed my weak spark. Electronic ignition needs good grounds to work properly even with good components.
 
Mako21 said:
Well, good point , I changed the ignition components, not sure how to check the spark resistance other that grounding the plug on the valve cover and seeing it spark.

Is there a procedure or write up for this? I imagine I’d need an electrical tool to diagnose this.

I just keep coming back to the carb and putting more time, effort and money into it.
Click to expand...
Buy a cheap spark checking tool from harbor freight or similar. Set the gap to about 1/4 inch and watch for a nice blue spark when cranking. Follow the directions for hooking it up.

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1. check to make sure choke is opening all the way
2. check float level
3. check timing - both initial and total
4. Is the cat plugged ?
5. What brand and heat range of spark plug?
6. Coil output ok?
7. ECU working ok? Grounded?
8. Is the heat riser flap frozen shut in the exhaust manifold?
 
Is the air filter element stopped up with dirt?
 
Thanks all for the suggestions. I’m going to leave the carb as is for now and start focusing on ignition related. The choke and exhaust flapper are working normally, I’ve read numerous threads on those.

Time to check the grounds, coil, ECU and start researching the ins and outs of the system. Ignition system has been in the back of my mind for a while now.
 
It is not ign.
If you can screw the idle mixture screw in until it seats & the engine does not stall or at least run very rough, then the engine is getting fuel at idle from somewhere else.
Check the PCV valve; it should rattle when you shake it. If that checks out, remove the carb & see how much transfer slot is visible the t/blade at idle.
 
Pull the dipstick and smell it. Does it smell like gasoline? Is the oil level higher than it should be? --> --> --> faulty fuel pump leaking gasoline into the crankcase, which gets sucked into the intake tract via the PCV valve—progressively more and more as the engine warms up. This would explain your constellation of symptoms, including the engine staying running with the idle mixture needle seated.

But so would a carburetor too faulty to be fixed with a rebuild.
 
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