Carburetor and fuel question

[glennstar67]

Hello everyone. I have a question hopefully you guys can help me with. I just installed a new Edelbrock AVS 2 on my car. Idle and throttle response are much better. However sometimes when I take off from a stop the car will hesitate and try to die. Then it will backfire through the carb a few times and then run fine again. Had the same problem with the old carb as well. Fuel pump was recently converted from manual to electric. Could it be a p.o.s. pump? I personally did not replace it. Gas tank has been removed and cleaned and all fuel lines replaced. I am stumped. Thank you all in advance for your help.

 

[WileE]

Thr carb will transition from the idle circuit to the main metering system. However, if you push the pedal down quick enough, the accelerator pump system will add fuel because there is instantly no vacuum to draw fuel from the main circuit. First, check to see if you get a good squirt of fuel from the accelerator pump off idle.

 

[glennstar67]

Thr carb will transition from the idle circuit to the main metering system. However, if you push the pedal down quick enough, the accelerator pump system will add fuel because there is instantly no vacuum to draw fuel from the main circuit. First, check to see if you get a good squirt of fuel from the accelerator pump off idle.

 

[glennstar67]

fuel delivery seems fine

 

[Photon440]

Does it happen repeatedly, meaning you can make it present the problem at will? When it's still cold, or after warmed up? And do you have enough initial timing advance?

 

[65-440]

Have you checked timing yet? Mechanical advance working?

 

[moparedtn]

Timing is either retarded or the carb accelerator pump needs adjusted to give more shot on
throttle tip-in.

 

[ruffcut]

My thought was timing also. If both carbs act alike, sounds more like timing, vacuum advance. ruffcut

 

[WileE]

Yes, the timing would be my next check after confirming the accelerator pump is functional. See if your vacuum advance is functional.

 

[glennstar67]

Ok I will check the timing. But one thing I have noticed while watching the fuel filter with the car running is that every once in a while the fuel inside will completely bubble up like it's boiling and then it will go back to normal after a minute or so. I think this is when my problem is happening while I'm driving. Any thoughts on this? Thanks everyone.

 

[69Bee]

Pay attention to your altitude also; around 5000 ft in your case. The new carb was adjusted to sea level when built, and you need to take that into account too.

 

[Nevada dan]

just advance the distributor and see what happens , you can always put it back

 

[glennstar67]

Pay attention to your altitude also; around 5000 ft in your case. The new carb was adjusted to sea level when built, and you need to take that into account too.

 

[glennstar67]

That is true. But the old carb that was on the car was doing the exact same thing and I had that one power tuned here.

 

[69Bee]

That is true. But the old carb that was on the car was doing the exact same thing and I had that one power tuned here.

I understand, but the same issue could have affected it also. You basically have the same issue we do here at the same'ish altitude, less air. I am not implying that this is the entire issue, but keep your altitude in mind. One change it to go to a lighter jet rod spring, and a buddy of mine sets the float level a little lower too to prevent flooding.

 

[Nevada dan]

the higher the altitude the more advance need too

 

[glennstar67]

I understand, but the same issue could have affected it also. You basically have the same issue we do here at the same'ish altitude, less air. I am not implying that this is the entire issue, but keep your altitude in mind. One change it to go to a lighter jet rod spring, and a buddy of mine sets the float level a little lower too to prevent flooding.

Ok. I will check those out. Thanks for your help!

 

[Ernie ingling]

Probably to lean turn out screws 1/4 then drive. If better turn a bit more

 

[RJRENTON]

Pay attention to your altitude also; around 5000 ft in your case. The new carb was adjusted to sea level when built, and you need to take that into account too.

IMO.....Yes, altitude influences the carbs fuel delivery settings. Typically, the carb is jetted LEANER by one or two jet sizes (smaller), for both primary and secondary metering as altitude increases. OR, in the Carter/Edelbrock/Weber carbs, an INCREASE in the diameter of the cruise step and power step of the primary metering rods will lean the fuel mixture. Changing the primary metering rods step up piston springs will affect WHEN the change occurs not the overall amount of change. Remember, that the idle and off idle fuel calibration feeds are in the primary booster venturii clusters as drilled orifices that are not adjustable. These primary booster venturii control the fuel feed to the idle mixture screws. Changing the primary metering jets and rods do not effect idle and off idle fuel feed circuit. Changes to these drilled orifices in the primary booster venturii are possible but difficult to reverse. Just my opinion of course.
BOB RENTON