I agree that it's timing, but I remember when I swapped my 750 Demon on an old ignition system and all it would do is backfire.

MAKE SURE that you have enough voltage going from your distributor to your plugs. You've probably already done this but I just wanted to mention it, even though you have HEI. Good luck man

 

I toke the distributor from carb'd 3rd gen bird changed the cab,rotor and coil to Jegs brand and I still think the distributor is tired or something I will swap another distributor and check it and I re-used the same MSD wires that my TPI had I will change the wires tomorrow

 

Try getting the number 1 cylinder back to TDC and redue the firing order again. The rotor should be pointing at the number 1 cylinder, slightly to the right of the carb if your looking at it from the front of the motor. I have had this happen many of times. Check your power valve/valves in the carb. I think they will cause a carb to backfire Its probably got 8.5 or 7.5.

Check out this website, the power valve section-http://www.mortec.com/carbtip1.htm

Hopefully this will help you out. You might want to up your iginition power or your mechanical fuel pump. I know holley and edelbrock make high performance mechanical fuel pumps

 

I had 130GPH fuel pump before but I thought the diaphram is damaged because the fuel pressure was reading 7-9PSI and then slowly the fuel pressure go down to 0 and the motor shut off I changed the fuel pump back to the stock one and the same thing happened then we opened the gas tank to take off the in-tank fuel pump I will put the 130GPH fuel pump back again and about getting the number 1 cylinder back to TDC thats what my friend told me yesterday if it wasnt at the TDC it will backfires,if I put the piston bck to TDC and the rotor is not in the right place how can I turn the rotor? do I take off the distributor and turn the oil pump shaft?

 

Just take the distributor out and turn your oil pump shaft with a long flathead screwdriver. You can just take the distributor out and drop it back down, turning the rotor at the same time to get it to the desired position

 

or you can rotate the wires on the cap too. #1 can be any one of the posts u want it to be.

also #1 tdc with both valves shut. gotta pop a valve cover to see that.

 

You could just do the old school test. Take out the #1 plug out, put your thumb in the spark plug hole, have someone bump it over until it blows your thumb out, or you can just go by your timing marks(if they are right)

 

Im facing another problem the backfires suddenly stopped but when I try to start the motor its like hard to turn this never happened before the battery is good and the starter is brand new from Summit that can turn over 12:1 CR

 

Sounds like timing is too far advanced.

 

can,t believe that no one has seen this in the pic. The vacum adv. on the hei is not a ported vacum. He has it hooked up in that manor. The vacum port on the base of the carb is vacum all the time. It decreases when accel. momentarily. The old point type is ported vacum, not the hei. Unplug the vacum hose, put you timing on 39. total to start with then plug it back up. It will idle better plus start with a little retard

 

I cant play with the timing because the timing cover is the original 350 with the stock timing pointer I need a timing cover that has no timing pointer and put the right timing pointer for dampner and Im not using the all time vacuum at the base of the carburetor Im using the one in the metering block anyways I started the motor it fires but it throws carbon from the exhaust and when I turned it off a white smoke comes from the carburetor my engine is cursed

 

yes, something is def wrong with the timing. could even be cam timing too. you need to get the right setup timing pointer and go from there. all your doin is guessing and that wont really work. as youve found out. are u positive the timing chain is on perfect?

 

thats what im working on today I will check the timing chain notch its def not inline

 

Thats what it sounds like. I've had that happen also. Def need to get your timing marks worked out. Don't feel bad, I believe everyone on here has been through this before...haha. I know I have. Just go back and double check everything, its more than likely something really small.

 

I started to hate the car after putting the 383 there I just hope the backfires from the timing marks

 

regarding the power valve in the carb what can happen if the engine has low idle vacuum and you have a high number power valve, the low vacuum drops at idle causes the power valve to open when it should not and supplies too much fuel. This would not cause a backfire at idle. Backfiring as in through the intake on a carburated engine is caused by a lean condition, the mechanic that said that was mostly correct.

I don't think it's cursed, I think you're just not doing the basics which are very simple. Diagnose it in a systematic manner. Start with the running condition of idle: rpms less than 1200.

first, make sure the firing order is correct and the wires off from the distributor are going to the correct cylinders.

try to verify best you can all the timing measures are correct, with the timing pointer set at 0 on the balancer you are actually at top dead center on cylinder #1. And the distributor is not 180 degrees off.

i see in your pic you have a fuel pressure gauge off the carb, that's good. it should tell you the carb is getting fuel. At idle if you have more than 2 psi and you're having problems it is not a fuel pump issue; you will most likely have problems under power at high rpm but for idle there is enough fuel. And unless it is more than 10 psi fuel pressure at idle there is nothing to worry about there, the norm is 6-8 psi and when under full power over 2 psi is good.

I agree with flirtinwithdisaster, I think you have the vacuum advance of the distributor hooked up wrong. The way they work is it is hooked up to intake vacuum, when vacuum is high the distributor advances a little for economy; when under power and vacuum is low there is no extra advance so there is no detonation. You disconnect this vacuum advance hose from the distributor when setting base timing- pull the hose off the distributor side and put a bolt in it to plug it so there is not a huge vacuum leak. Set base timing to 10 dbtdc. Reconnect advance hose, start engine, and with the high vacuum at idle it should advance timing a few degrees, whatever that distributor was built to do. But for base tuning I would disconnect the vacuum advance, it will make carb tuning easier at idle and quickly pinpoint what is causing the backfiring.

With engine running at idle, vacuum adv disconnected and intake manifold port plugged and you're sure of no vacuum leaks, timing should be at 8-10 dbtdc, now tune the carb. Step #1 in carb tuning is always set the float level, everything runs off of this. Don't turn any mixture screws until you know the float setting and fuel level in the bowls are correct. If you can, put a vacuum gauge on the intake manifold and observe the reading as you set the idle mixture screws, go for highest vacuum reading. If at this point you still cannot get a smooth idle then begin looking at lifter preload and camshaft alignment; if it is one of these it will be evident by a vacuum gauge having an erratic reading.

here's some results of google = distributor vacuum advance
http://www.chevyhiperformance.com/ho...438/index.html
http://www.stoveboltengineco.com/howto/vac.htm
http://www.highperformancepontiac.co...ech/index.html

interpret vacuum gauge:
http://www.secondchancegarage.com/public/186.cfm

 

Sounds like the dist. is off a tooth. When you go to put a new timing cover on put it back at TDC and see if its dot to dot. Drop the dist. back in and make sure its pointing at #1 cylinder. Before you fire it, make sure your valves are set right. Are you running factory pushrods?

 

1 FMF I checked everything you said before and no use the carb is tuned everything is fine I stil didnt get the puller for dampner to open up the timing cover and check the notch again

1 BAD TA yeah the distributor was off two tooths not one tooth we put it back and still the car wont start I guess the timing gear is too advance

 

What about the pushrods? Timing chain stretched perhaps?

 

the pushdrods are the stock ones the short ones and its not a timing chain its a timing gear and I think its off a tooth I opened the timing cover yesterday I will change the timing gear to a noisy one and change the timing cover and put the correct timing cover and timing pointer for the timing light,is it possible that the intake valve is not set properly?