This is for my 68 firebird the info on it is in my sig 455 750 demon carb. When i give the car light throttle it drives fine and when im going 10 MPH and above and floor it it is fine but when i am at a dead stop and floor it the car basicly just dies then i will let my foot up off the gas peddle and eveything will be fine any ideas what can be causing this. I do have my VS closed off i havent had a chance to adjust that but my primarys are adjusted fine.

When i did have my VS opend up i still had the same problem this creates a problem if i want to race i wont be able to floor the car off the line.

 

How old is your fuel pump?

How high is the fuel float set at?

 

The fuel pump is a new holly red and the floats are set about 1/3 of the way up as i can see in the little glass window.

 

When the car is in park and i floor it all the way there are no problems but when it is in gear is when it does it.

 

hehe, i remember one day, i had just did my plugs, and i half way connected the battery terminal to the distributor. IT drove me all the way to work, and then in the parking lot it jumbed or died when i gave it gas while moving but sure enough when i put her back in neutral shesd come right back. When i parked she was all there.

well later the next day she completely stopped. I checked cap, and snipped it right back in, problem solved.

Might be different for you, but just my .02cents.


MTH

 

It did this when i had the stock point ignition system on it i have recently upgraded to a mallory unilight distributor and a ignition box so i have a feeling it may have to do something with my carb but im not sure im new to carbs so i am still learning. But i know this problem shouldnt be. Basicly every part on the enigne has been replaces from the oil pan up the the carb and exhaust etc. The enigne has about 100 miles on it so far.

 

I'm not too sure about Demon carbs, I've mostly read up on the Quadrajets.... but what size are your jets? Sounds like your a/f mixture isnt right. You're getting too much of one or the other. You can pull a spark plug and read that to find out.

 

I will pull a plug later this week and post a picture of it. But why would it only do it from a dead stop not when im going like 5 mph. Right now the carb is how it came from the factory i havent done anything with jets or springs at all.

 

possibly there's enough extra gas going in to keep the car going at 5MPH that when the secondaries open up it gives it an extra little bit of time to get more fuel in there. Is there a bog when you whomp on it from a roll?

It sounds like your secondaries are shoving too much air in... either that or you arent pushing enough fuel down there... I'm not an expert by any means though... like I said, I've only had minimal research on Q-jets as my main source of carb information.

 

When i whomp on it from a roll it just dies i need to be going at least 5 mph to floor it for it not to die. When i let my foot off the gas peddel after i whomp on it and it dies it will come back to life and be fine. My fuel pressure to the carb is at about 6-7 PSI

 

Do you have your accelerator pump set up right? Whats your ign timing set at?

 

I never touched my accelerator pump that is the thing on the driver side by were the throttle cable goes correct. I dont know how to set it at all. Could that be my problem

My timing is set at 8 degrees which the car seems to idle and run perfect with i have tried different settings and 8 seems to be the magic number.

 

On my Holley, I set the accelerator pump linkage so that there was no slack in it... not tight, but no slack. It should 'pump' whenever you move the throttle open.

 

After finals this week i will read my manual on the carb and learn what the accelerator pump is i have no clue what it is or where it is.