okay i think i might have narrowed down my problem ive been having with my car. me and a friend checked out a few things last night and one thing that got us is that when we opened the top butterfly vavles for the secondarys and looked at the bottem butterflys and tryed opening the botten ones they only opened about a 1/4 to almost a 1/2 inch and nothing more. and my friend thinks that the fuel gets stored up there and thats what causes this backfire ive had. but it was a back fire from the exuast and not the carb. becuz i was acclerating at the time. and then the car stumbled and then boom backfired like a shotgun.

so if anyone can give me there opions on what it is that would be great other wise im goin to buy a brand new edlebrock 600 cfm and put that on. becuz ive replaced fuel pump, fuel line from pump to carb, fuel filter, and plugs. i have almost new plug wires that are only a yr old and have about 300miles on them. and suposively everything inside the distributor was replaced but i also have new cap, rotor, coil, etc. and my timing is also good becuz i got that checked yesturday.

so if anyone can help me thank you.

tim

 

no one huh?

 

There is a little lock-out tab that is pushed out of the way when the choke comes off. It is possible that it isn't moving out of the way like it is supposed to when the choke comes off. That little device is located on the bottom passenger side of the carb. Of course, if you and your friend were looking at this when the choke was on or partially on, then your carb was working the way it was supposed to.

I'm not saying this is the reason for your backfiring, though. In fact, I would say it is not. It is more likely that the secondaries are in fact opening too soon, which is regulated by the air valve flap on the top of the carb. That is controlled by the vacuum choke pull off, and the AV tension spring (tech articles have more detailed information about that).

 

Just in Case... did you check your timing?

Also... is the carb running rich? Is so.. how rich?

get a reading from the spark plugs..

Also... what is your idle speed? for automics I leave is 900 rpm... for manual is 750 rpm.

 

i got the timing checked at work(pepboys) and the mechainic said it was good. i idle around 900 maybe little less maybe little more id have to check again i havent driving the car in about a week. and ill have to check the secondary rods to see which ones i put in. i think i might have put the richest ones i had in but im not sure on the letters. i could find out tomarrow.

 

Quick one....Are you using the CC Q-jet or Mechanical one?

Back fine on the tail pipe tell me that some how there is either too much fuel, or the car is reving to high...

Vacuum leack???? Is possible.. although backfire with vacuum leack are MOSTLY associated thru the carburator not the tail pip...

Also.. Belive it or not.. when I decided to scrapth the computer on the car an when with a Mallory HyFire CD Box, Mallory COmp 900 Vacumm Advance Unilite Ignition, and a mechanical Q-jet I have my timing improved DRAMATICALLY..

I belive something was not right ON MY STOCK IGNITION..

Let me know on this!

 

well dammit i forgot what i was goin to say...oh yeah the computer has been ripped out and everything converted to the vacume advasnted set up. like for the dist. and carb and all that fun stuff. also im leaning towards what u were sayin about the meterin rods before and was thinkin. that if i did put to big of them in could that be screwing me up. and havin all that extra fuel sitting in the carb and then boom.

also i was thinkin of changin my ignition to a MSD pro-billet hei dist. (hoping it has the little vacume advansted thingy on it) and then do all new plug wires too when i change that. but right now ill check and see if its the carb that screwin up. do u have anymore things i could check and see or no?

 

Your idle is rather high at 900 rpm for an automatic.

Reset it to 750 - 800 rpm.

 

ok il do that tomarrow morning when the car warms up a bit. also if u listen to the exuast it kinda sounds like im missin sometimes. but i have brand new spark plugs in and the gap is set right on all of them. what could be casuing this or could it just be the way the exuast sounds or the way the engine is running? becuz the engine was rebuilt a few owners ago and it could be possible that the owner changed the cam and could that be giving me this sound?

 

I think your timing is too far retarded....I can't rememberif it's too far advanced and backfires thru the exhaust or the intake...I would worry more about timing than seeing if you carb is loading up with fuel....usually too much fuel gives you a bog on take off and doesn't affect backfires...if your carb has too much fuel at idle i.e. running rich then you will have black smoke coming out of the exhaust. I would worry about your timing before messing with the carb anymore. Hope this helps

 

I have a '86 Trans Am (automatic) with a CC Q-Jet, and I idle at about 600 RPM.