Stumble during acceleration

What do you have (spacers and/or gaskets) between the carb and intake manifold?

I,m having the same problems. I made sure my MDS was grounded well, never underestimate the need for a good ground.

Bogging, carb backfires or stumbles are most often due to lean outs. Many areas to look at with tuning a carb. I only know Holley's but I think demons are similiar. You might need a different vac secondary spring that opens the secondaries sooner. A larger jet might help as well. Lastly a larger squirter would allow more enrichment in the transition from idle to accceleration. Best to get a carb tuning book as they provide graphs and pointers on where to look first and what size to use. Look at jet sizes, squirter sizes and different vac springs. It is a black art and requires some trial and error.

It helps to make sure the spark is strong and that the spark plug gaps are to spec. Elminating spark issues allows you to concentrate on fuel problems.

Lastpushbutton, my experience with MSD's is that when the fail, they fail. No spark what so ever. A dropoff in a specific RPM band does not seem reasonable, check caps/rotors, wires and plugs if the are good and the wires ohm out then fiddle with the carb.

I do have a plastic carb spacer.

...I'am guessing the Vacuum Advance could be hooked up to the WRONG vacuum port (timed spark) which would be incorrect. It SHOULD be connected to 'Full' planum vacuum, and NOT to a Single Runner where you would get a 'Pulsed' vacuum. Second the 'Accelerater Pump' may be adjusted improperly. Last, are You 100% sure that the 'Timing' setting, done with the timing light, was set correctly!?...

A demon I assume is like a holley. The accelerator pump adjustment is too tight. The car is getting to much gas . Loosen it up so there is .015 clearence between the arm and the spring. Its the carberator. Just because is new means nothing. also if it vacumn secondaries try changing the spring it sounds like the secondaries are kiccking in too early. If its mech secondaries they could also be kicking in too soon.

I have the 650 Demon also, it's important to make sure there are NO vacumm leaks. Over tightening the carb can crack the phenolic spacer (many years old) and cause leaks or allow the the base of the carb to be warped allowing air leakage at the base. I would replace the spacer with an Edelbrock gasket #9266 or #9265, they are similar to the orginal thinkness (.320") of the phenolic spacer.
Also check the thermal-vacuum valve, this device should be bypassed if not connected correctly. Use the connection that the Barry Grant instructions indicate for vacuum advance to the distributer.

quote:

Originally posted by Throttle man:
I do have a plastic carb spacer.

A vacum leak can cause the symptoms you describe.