Part throttle/low rpm "bogg/surge"

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1972dodgedemon

1972dodgedemon

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I have sifted through what must be hundreds of threads on low rpm stumbles and have not found any one who has had the same symptoms as me. I am pretty new to tuning carburetors although i have a healthy knowledge of how they work.

The problem appeared after i adjusted the secondary butterflies on my 625 vs "road demon" carb in order to be able to lower the idle to where it needed to be.
Everything was working famously for a few days until i developed a low rpm part throttle, up and down, bog/surge. I have tried re-adjusting the butterflies and tuning the idle mixture screws and have managed to reduce it to being barely noticeable while cruising at 40 mph in 3rd but there is still a very noticeable bog on the low end no matter how much i feather or stomp the gas.

I have also been having issues with my vacuum advance distributor. I have followed MP guidelines for setting mechanical and vacuum advance to equal a total of 55 deg advance. The mechanical advance is all good but i cant turn the vacuum advance down enough to get that total of 55 degrees. As of now i have the vacuum advance attached to the direct manifold vacuum port. Should it be attached to the throttle sensitive port?

My third issue is that at idle in gear with my foot on the brake especially with loads on ex. radio, headlights....etc I'm seriously draining the battery. My ammeter indicates about -10 amps. Idle in N 750 in gear 500.
 
I have recently replaced the voltage regulator and I'm planning on replacing the alternator. I'm just wondering is this in gear stopped drain normal? I mean even with all loads off in order to break even on draw i would have to set the idle in neutral at 1100 rpm....I have had the battery tested (made sure it was fully charged) and it IS a good battery.


1972 dodge demon
318 factory everything except carb and intake.
 
Get your timing right first. I would set it a 10-12* BTDC with the mechanical at around 26, for a total of 36-38*. I would also look for a vacuum leak. Put some water in a spray bottle and with the engine running spray a mist of water around all mating surfaces of the intake and carb base. You will notice a sputtering if you find one. I hook my vacuum advance to ported on the carb.
 
1972dodgedemon said:
and by ported do you mean throttle sensitive port for the vac advance?
Click to expand...

Yes, the one with no vacuum at idle. Also, have you checked your fuel floats? Do you have a Fuel Pressure regulator? What fuel pump?

Not sure on your electrical issues, but you should get a charge at idle. Do you have electronic ignition?
 
I have the factory style mechanical fuel pump with no regulator. From what i can tell, it's not over filling the fuel bowls or bypassing the needle/seat valve. I have converted it from the factory ignition to the mopar performance electronic ignition.
 
Hi. I hope this will help.
You cannot shut the secondary butterflies prematurely. They require to be open to meter fuel through them. If you shut them too low or completely you will stop the fuel flow in the secondary circuit. this will put the secondary circuit to "sleep" so to speak. So if you you accelerate or put your foot down you will stumble till the secondaries wake up upon the cracking open of the butterflies. There will be a delay. Both Holley and Demond carbs have separate fuel bowls thus both requiring constant metering to circulated fuel through them. If you don't meter the secondary fuel and drive constantly light footed you will never open the secondaries. (for months on end unless you are a lead foot). This will clog up your secondary fuel circuit. There is a procedure to adjust the butterflies on the secondary to the correct opening. You cannot veer from this adjustment. (small tolerances permitted). If your idle is too high adjust the primary butterflies only. If your idle is still too high, and the primary butterflies are COMPLETELY shut, you might have a leak somewhere or the secondary butterflies are adjusted too open. Pull the carb off and check the adjustments, and then check the timing and make sure its on the ported vacuum not the full vacuum connection on the carb.

Regards
Billy D...
 
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