well here we go im cruisin home from town the other day when i get to a stop sign well long story short car starts to shake and lose power i can hear pow pow pow through the carb i was close to home so i park it for the night next day i go out buy plug wires needed new ones any ways install those doesnt help one bit set the iab again 50% check timing its good unplug ecm still does it im new to cars kinda but im stumped it only does it when u give it throttle and seems to do it more underload im afraid to drive it because i heard a lean condition can cause backfiring but it idles fine so i need help this is my ddriver 350 with ccqjet on top thanks

You might have a vacuum leak somewhere causing the timing to go apeshit crazy. But yeah thats what it sounds like to me, timing.

I would guess your cam, one of the lobes is trashed and allowing one of the intake valves to stay open. Pull the plug wires one at a time and see it the poping goes away so you can narrow it down to what cylinder is causing it. If you find one then pull the valve cover and watch the rockers for that cylinder at an idle.
If I am right one will be barley moving compaired to the rest.

i think iroc zz is right which is scary becasue the timing is dead on and ive checked everything electrical so i doubt it is something there when im driving i can feel it vibrate at a certain time like when it reaches a certain cylinder or valave like you said what would caus ethis and i will definely need a new cam

How old are you cap/rotor/plugs and wires?

i belive it is a valve train problem i replaced plugs wires and have good spark im gonna do a compression test to see if it one is low

Could it be the cam? I would figure a cam can only really loose a lobe. So I guess if he has a wiped out exhaust lobe it might force the exhaust through the intake. What about a wandering cam? If it comes forward enough it can really trash the timing causing the backfire. And that would only happen every now and then wouldnt it? He may want to look at the front of his timing cover and see if it has been bent out and is touching the water pump.

well ill keep that in mind and check for it couldit be a bent push rod im gonna do a compression check anyways to see whast going on
i may have forgot to mention the timing is dead where i set it at idle maybe it isnt advancing right but the timing seems fine just got a cylinder missing im sure and now it smokes like a chimney whiteish with a lil blue (oil) hahah im wonderin if one of the valves isnt stuck open allowing oil into the chamber or if i cracked a ring

Sorry to say I would almost guarantee its your cam. Same thing happened to me last year. Idled fine and backfired through carb at higher rpm. I was in process of buildng a 350 for it anyway so was no big deal to me just had to rush it up. Pulled 305 (notorious for flattening a cam lobe) and pulled cam out sure enough one lobe was completely flat. Just gives you a good reason to get you a 350 and drop it in. GL

well it has a 1975 350 with the the lg4 top end(ccqjet) on it the cam is some aftermarket cam the kid put in it before he supposedly rebuilt the motor( yikes shoulda never bought it) when we got it we found it was oil hungry then replaced valve seals that slowed it but when we put the air hose on number 8 to hold the valves up we could hear air moving cuz the idiot prolly stacked the rings im gonna pull the valve cover see if i can find anything if it is the cam will i prolly have to pull the motor? if so i might do a re rebuild lol but with new pistons and other various upgrades.

Was the air going into the crankcase, exhaust, or intake?

You've probably got a basic problem causing loss of compression in one or more cylinders. Mine was a broken exhaust spring - idled completely scary weird, didn't seem to affect WOT performance (compared to how it did after the springs were replaced).

couldnt tell where it was goin you could just hear it but it seemed like it was going through the ring spaces into the crankcase couldnt feel air anywhere else and the springs were fine we removed them and replaced valve seals none were broken

pulled valve covers today just to look and saw nothing outta the ordinary i coudlnt tell if any pushroids were bent everything seemed to be tight to spec and the rods would spin when under no load weird might have to pull intake to see what the cam and lifters look like

Did you try cranking it over or starting it with the cover off?
It should stand out like a sore thumb if one of them is not moving as much as the rest.

well i think i got it you guys are gonna want to shoot me for being so ignorant i being the smart kid i am (not) figured since i had changed the plugs and wires thing would be great well i sent my mom with a piece of paper to buy plugs about a 2 weeks ago long story short i ended up with the wrong ones didnt know at the time so i pulled them tonight before i dug to deep in the motor and found 2 had fouled out and were not firing ( thats the part where stupidity plays a key role) so tomorrow i am going myself to buy new plugs this time even possibly a new cap and rotor just wanted to say sorry for the stupditiy and wasting your guys time thanx for the help any ways it was a good learning expirience

dang still problems replaced plugs still no cureive got spark on all plugs checked it but 4 and 6 arent firing did compression check on 4 said 0 psi weird checked 2 it boucned up to 100 psi thats all the farther i got i was wondering if this could be caused from the kind not putting in hardened valve seats and maybe they are going bad mottor has about 6000 mi on it

I still say pull the valve cover and watch the rockers for number 4 and 2 while it is idling and make sure they are moving like the other cylinders.

hopefully your not in my position just got threw putting in a new comp cam in with vortec heads i did all the work besides setting the valves i got called out of town so my buddy set them for me well he tightened 3 of them so much it bent the valves and now i have the same problem you do of course my supposed friend hasnt been back to fix his fu** up

wow man i thought had it bad im hopin this isnt something thats gonna require pullin the motor lol

I dont have to pull the motor just got to pull the heads back off, either way its a lot of work that im just getting fed up doing getting burned out on mine hope you dont get that way with yours good luck with it