Fuel or spark problem?

[67dodgedartconv]

I have a 67 Dart with a newly rebuilt 318 with a small cam (little lope at idle but still enough vacuum for my power brakes), and new street demon carb (thermoquad type). Engine ran well for a few months. Idled well at 800 rpms and would do a burnout with my 2.76 gears. Few weeks ago engine would just flatten out with a continuous stutter over 2000 rpms and then would not want to idle either. Engine would often stall when coming to a stop sign. Sometimes when flooring the accelerator car would stutter then surge, going back and forth between stuttering and accelerating properly. I replaced my fuel filter which did have a fair amount of very fine black particles in it. It did not help at all. Now the engine is hard to start and will not idle at aIl. I removed the air mixture scews from the carb and shot carb cleaner in them. Replaced them at 1 3/4 turns out but this did nothing. Car has a Pertronix Ignitor 1 conversion which has performed well. Replaced the coil with another pertronix coil I had but no difference. Thought electric choke might be closing but it is open. Mechanical stock type fuel pump is only a few months old and the fuel filter is full of fuel. Looking for a logical plan of diagnosis without buying a bunch of new parts I don't need. I guess hooking the fuel line to an external gas can would be a start to see if fuel sender sock is plugged? Any help is greatly appreciated!

 

[DesertRat]

Sounds like fuel to me. Unhook the fuel line on the carburetor side of the fuel pump and turn it over. Unhook the coil wire first. Pump the fuel into a container and dump what you pump into your lawnmower. This should confirm or not your fuel situation.

 

[67dodgedartconv]

Sounds like fuel to me. Unhook the fuel line on the carburetor side of the fuel pump and turn it over. Unhook the coil wire first. Pump the fuel into a container and dump what you pump into your lawnmower. This should confirm or not your fuel situation.

Fuel pump is working, saw fuel filling clear plastic bottle.

 

[Bill Crowell]

67dodgedartconv, I can't answer your question but I am certainly going to follow your thread because I have 4 older Mopars with LA engines and Thermoquads, and they sometimes do the same thing. I'm looking for a down-to-earth (cheapskate) troubleshooting procedure. Thanks for posting.

 

[Mattax]

Replaced them at 1 3/4 turns out but this did nothing

Your car is not stock anymore.
Therefore you can not tune the way is done for a factory setup.
At best the factory setting are a now a baseline.
Since its not a factory carb, the turns out doesn't mean anything now.

You've confirmed the fuel pump is working.
If you can take the top on that carb easily, you check the fuel level as it sits.
^Take combination square or machinist rule or whatever you've got that wont's be destroyed by fuel and measure the fuel hieght. Compare that with the recommended fuel level in the instructions manual for that carburetor.
^ If not, then you can for now assume the float level is correct, or remove the carb and check it dry. If at some point there is evidence of over filling (fuel coming out of the boosters at idle, or after shut down), then you must adjust the fuel level (float setting).

Remove a couple spark plugs and see what they show.
If they are carbon fouled bad enough, then you know it is too rich at some or all situations.
^ Clean or replace the plugs, regap, reinstall, etc.
^ Check float level
^ check choke settings.
^ Reinstall, start, and with the air cleaner lid off, when the choke is fully open and you've kicked down to base idle, turn the mix screws in until the engine starts to slow down. Then open each up maybe a `1/4 turn. That should be about right in gear.

If turning the mix screws in or out makes no change, something isn't set up correctly. Either there's internal fault (dirt for example) or the throttle is set too far open, or maybe something else.