Small Block & Big Block Chevy Specific - 383 back fire !

finally I swapped the 383 in my 92 Z28 and we cranked it after few tries it back fires through the carb it only back fires if I open the secondarys before starting it up and it fires up and everything was good I faced a problem with fuel it wasnt enough or let me say the mechanical fuel pump couldnt suck enough fuel from the tank because the in-tank fuel pump wont let the fuel pass easily so we dropped the tank today and toke off the fuel pump and replaced it with 3/8 hose and hopefully tomorrow everything will work great,I asked the mechanic about the back firing he told me the engine dont get enough fuel so thats why it back fires :confused: I really didnt buy that excuse :confused::confused: this is my set up let me know why my engine back fires

383ci 5.7 rods 11.3CR
Edelbrock E-tec 200
Edelbrock air gab RPM
750 DP holley
236/242 520"/540" 110lsa on 1.5 stock rockers
1" carb spacer
MSD wires
Jegs cab,rotor and coil
Platinum spark plugs
Hedman Headers LT

I was thinking about the timing well I dont know im really confused right now

Timing

tomorrow I will open the timing cover and check the notch if its inline or not this picture will show you the position of the distributor

http://i102.photobucket.com/albums/m86/6666_02/IMG_0820.jpg

its in retard position so I guess the notch on the timing chain is off the line

Try to advance the dist by turning it counterclockwise, move it a 1/4"-1/2" or so at a time and see what you get.

Is that a factory HEI from an early car or one from an 80's Camaro with a cumputer controlled Quadrajunk?

which way to turn the distributor to advance? Im confused about this and its a factory HEI from early car

If your looking down from above turn it counter clockwise to advance it, you'll be moving the contact point in the cap closer to the rotor hence advancing the spark. If you go the other way you move away from the contact point creating retard.

Sounds like timing, but damn, why the heck did you leave the stock pump in there in the first place? You did right by installing a 3/8 line, it is what i do, will work fine for you.

Timing or a whiped cam. Assuiming the motor is new, its probably timing.

Sounds like timing, but damn, why the heck did you leave the stock pump in there in the first place? You did right by installing a 3/8 line, it is what i do, will work fine for you.

I told the stupid mechanic to remove it while he was installing the ring and pinion he told me it wont effect anything,do you suggest that I open the timing cover and check the notch? or should I play with the distributor?

92builtbird the cam is new I dont think there is anything wrong with the cam or the engine at first I was thinking the problem was from the carburetor but its brand new and then I noticed the position of the distributor so it was the timing from the first place

If you changed the cam you had to pull the dist out and re-drop it, crank the dist like I said and if you still have issues let us know. Crank it ccw until its hard to crank then turn it back the other way a little at a time to get it to run, then you can use a timing light to get it 100% correct.

You could also have the valves adjusted incorrectly but I think its a timing issue, unless you didnt break the cam in properly???

Keep slowly advancing the timing till it fires right up with hardly and hesitation what so ever.

MrOverkill its a hydraulic cam I dont think it need a breaking in and when the cam was installed there was no intake and dist

ZONES I will advance the cam as soon as I find a good tank

btw will a 4th gen tank will fit 3rd gens? I think the 4th gen tank is made of plastic or something like that right?

MrOverkill its a hydraulic cam I dont think it need a breaking in and when the cam was installed there was no intake and dist

ZONES I will advance the cam as soon as I find a good tank

Unless its a roller cam you MUST do a break in at 2500+rpm for at LEAST 10 mins. If you didnt do this and you let it ilde you have flattened your new cam I'm sorry to say. You have to heat cycle any new flat tappet cam hyd or solid it doesnt matter, it should have come with instructions on how to do this.

How long have you run it and did you let it idle at all???

Maybe do a little reading because advancing/retarding the cam is not going to cure your problems unless you installed it a tooth off. This is going to be a learning experience for you I think.....

Unless its a roller cam you MUST do a break in at 2500+rpm for at LEAST 10 mins. If you didnt do this and you let it ilde you have flattened your new cam I'm sorry to say. You have to heat cycle any new flat tappet cam hyd or solid it doesnt matter, it should have come with instructions on how to do this.

How long have you run it and did you let it idle at all???

Maybe do a little reading because advancing/retarding the cam is not going to cure your problems unless you installed it a tooth off. This is going to be a learning experience for you I think.....

oops sorry I didnt mention it was a hydraulic roller not flat :bang: even so its a roller cam I didnt let it idle always 2000+rpm but I faced that problem with the fuel delivery,anyways Im facing this problem with the fuel tank I hope I can find a better one do you know if a 4th gen Camaro tank will fit or not?

Advance the timing not the cam.

Run a hose from the pump to a fuel jug or gas can until you sort out the tank issue. You need to get the timing right with a light and as far as the cam a roller needs no break in just start it up....

Any luck or change yet???

Im back again I toke my car to a friend of mine he changed the jets to smaller ones adjusted the carb played with the distributor and still it back fires he told me there is an intake valve is not set properly but I dont know why I got this feeling that there is something wrong with the distributor today I will take my Camaro home,before a week I realised that the mechanic was using the retainer hose instead of the suction I switched them and now the car rev's very smooth and beautiful but when its cold it backfires too is there is something wrong with the carb? It's a brand new Holley double pump 750 I was thinking of switching to Demon vacuum 750 but I dont want to waste more money on something that will not solve my problem

I toke my Camaro home and it only backfires when cold since the carb has manual choke its fully opened and when I floor it quickly it back fires any advice please?

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?

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.

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?

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/howto/97438/index.html
http://www.stoveboltengineco.com/howto/vac.htm
http://www.highperformancepontiac.com/tech/vacuum_advance_tech/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?

yes. if you have too much preload on the lifters then that can prevent the valve from fully seating = open valve = backfire.

yeah, make sure there adj. right, and make sure they are the correct length.

also, if you did a cranking compres. test, that would answer that for you. atleast, let you know to look closer there or not. if you have less then 150 cranking press, with the sp plugs out, full battery, and the throttle held open. should be in the upper 100's. like 175. seen lots higher then that, but a typical 10.5 compresion sbc will be in that area. sorry for not goin back to remember what your particular eng. setup is. could even be in the really low 200's if you had a high compression motor.

whats the stock pushrods length? I checked the suggested parts for my cam and the size was 7.195 I will order few parts soon I guess I will add the pushrods too

and yeah I forgot yesterday I toke few pushrods out and a small piece on the side where the pushrods meet the guidplates is scratched bad it was touching the guideplates I will try to take a picture of it

here is a picture that shows you what happened to the pushrod

http://i102.photobucket.com/albums/m86/6666_02/IMG_1157.jpg

http://i102.photobucket.com/albums/m86/6666_02/IMG_1158.jpg

not sure what stock pushrod length is however that value is based on who knows what setup which is based on a block with a certain deck height, lifter size, head, and head gasket. Change any one of those things and that stock length value is incorrect. The smart thing to do is use a pushrod length checker and check your engine so see what you length you need. Google "rocker geometry" for the details, in short you want the wipe pattern that happens on the valve step tip from the rocker arm to be as small as possible and most importantly as centered as possible. You can also observe the wipe pattern resulting from the current set of pushrods and judge whether they're off or not. If your pushrod length is off that won't be the main cause of your current problems but it can result in poor performance at high rpm and will definitely result in short lifespan of the valvetrain and breakage. your pic is blocked for me at my current location, will try to look at it later.