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  #1  
Old Mar 23rd, 05, 6:09 PM
Resq302 Resq302 is offline
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Question Causes for backfire through carb???

Can anyone point me in the direction I need to look into? My 70 El Camino started backfiring quite badly through the carb with a ball of flame coming out. The carb has been running rich it seemed lately as there is a lot of carbon coming out of the tail pipe. The car prior to the carb being rebuilt was running rich and after the rebuild seemed better but then starting running rich again. During the rebuild, the float was also replaced. Where should I look to correct the backfiring problem? Is it that the carb is too lean or rich?? Might the distributor points need to be adjusted??? Any guidance or direction would be greatly appreciated as I am working on trying to get 2 vehicles running for the upcoming show season.

Thanks in advance,

Brian
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El Camino----The ORIGINAL Sport Utility Vehicle !

-1970 El Camino SS 396 (true SS, highly optioned car) AACA Senior Gold Winner (Hershey 2005) , 2006 Concours d'Elegance Star Award winner
-1969 Dodge Charger HP 383 ci. 4 spd AACA Senior National Winner (Herhey 2007)
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  #2  
Old Mar 23rd, 05, 11:48 PM
JRS70LS5 JRS70LS5 is offline
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Default Re: Causes for backfire through carb???

Carbs will backfire running lean,never seen one backfire running rich.Vacume leak will cause the engine to run lean, or timing will cause it to backfire.
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  #3  
Old Mar 24th, 05, 7:48 AM
forcd ind forcd ind is online now
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Default Re: Causes for backfire through carb???

i would start with a comp. tune up-plugs, points, dist cap, wires, set the timing-then if problems still there, chg the carb(dont know the engine setup, but over caming an engine will cause rich @ idle) or have someone look at it
could be almost anything-i have seen a cracked dist cap drive people crazy, makes the spark jump to another cyl
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Old Mar 24th, 05, 8:43 AM
Resq302 Resq302 is offline
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Default Re: Causes for backfire through carb???

The motor is the 402/350 HP motor that is stock. Under smooth acceleration it raises the RPM's fine but when you floor it is when you get the pop with the fireball.
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Morris County, NJ

El Camino----The ORIGINAL Sport Utility Vehicle !

-1970 El Camino SS 396 (true SS, highly optioned car) AACA Senior Gold Winner (Hershey 2005) , 2006 Concours d'Elegance Star Award winner
-1969 Dodge Charger HP 383 ci. 4 spd AACA Senior National Winner (Herhey 2007)
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Old Mar 24th, 05, 1:09 PM
Don Maddock Don Maddock is offline
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Default Re: Causes for backfire through carb???

Brian,remember in order to get a backfire through the carb,you have to be firing the cylinder with a intake valve open,so check carefully your electrical components as was mentioned by forced ind.
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Old Mar 26th, 05, 12:55 AM
Resq302 Resq302 is offline
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Default Re: Causes for backfire through carb???

Don, could a bad lifter be causing the backfiring??? I have been getting a tapping noise which I have thought to have been a bad lifter. I have brand new lifters and will probably be putting them in soon.
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Morris County, NJ

El Camino----The ORIGINAL Sport Utility Vehicle !

-1970 El Camino SS 396 (true SS, highly optioned car) AACA Senior Gold Winner (Hershey 2005) , 2006 Concours d'Elegance Star Award winner
-1969 Dodge Charger HP 383 ci. 4 spd AACA Senior National Winner (Herhey 2007)
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Old Mar 26th, 05, 8:08 PM
Don Maddock Don Maddock is offline
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Default Re: Causes for backfire through carb???

Brian,I doubt a lifter is your problem. A collapsed lifter wouldn't open the valve. As forced ind. recommended , I would go through things as in a tune up. One other thought that would give you a lifter ticking and a backfire, would be a broken valve spring on an intake valve,not uncommon on the early big blocks. Might be worth removing the valve covers and having a peek. Don
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Old Mar 28th, 05, 6:07 PM
Resq302 Resq302 is offline
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Default Re: Causes for backfire through carb???

Don,

I checked the adjustments on the rocker arms as I have had a tapping noise which I thought was coming from a hydraulic lifter. It comes and goes at any time whether it is warm or cold. It makes about 5 taps then goes away for a min, then does 5 taps then goes away again. Almost like it is taking a while to build up pressure in the lifter. While I had the valve cover off on the pass side where it seems the ticking noise was coming from, the springs seemed to be ok and nothing out of the norm visual wise. What would be a sign that a valve spring is broken?? I have never seen one before so unless it is very obvious, I don't know what to look for.

thanks for the ideas and help so I can get my elky back on the show circut for the upcoming season.

Brian
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Morris County, NJ

El Camino----The ORIGINAL Sport Utility Vehicle !

-1970 El Camino SS 396 (true SS, highly optioned car) AACA Senior Gold Winner (Hershey 2005) , 2006 Concours d'Elegance Star Award winner
-1969 Dodge Charger HP 383 ci. 4 spd AACA Senior National Winner (Herhey 2007)
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Old Mar 29th, 05, 1:05 PM
Don Maddock Don Maddock is offline
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Default Re: Causes for backfire through carb???

Brian,a broken valve spring is usually quite visible,so if you didn't see anything with a good visual inspection,they are probably not the source of your problem.Mystery noises,aren't they great!!
The backfire through the carb should be a good clue for us Brian,have you been inside the distributor and given that a good visual? Can you go back to when this problem first occured? Had you worked on anything or had work done on anything? The backfire through the carb and the noise are probably related so I have to go back to my original reply about firing a cylinder with an intake valve open. Don
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Old Mar 29th, 05, 4:40 PM
Don Maddock Don Maddock is offline
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Default Re: Causes for backfire through carb???

Brian,one other thought,is a spark plug wire that is cross firing to another plug wire or two wires that are crossed.Often times a motor will seem to run ok under partial throttle,but exhibit your symptoms when you get on it .Check your firing order and your wire routing also. Luck to you Don
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Old Mar 29th, 05, 4:46 PM
Resq302 Resq302 is offline
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Default Re: Causes for backfire through carb???

Don, I have not had the valve cover off yet but from when I was in there last trying to adjust the lifters, everything seemed fine and nothing seemed to be apparently wrong.

I pulled the plugs out of the engine today and they were completely black. I installed new plugs and they also became soaked in gas. Hence the black smoke coming out of the exhaust. I pulled the carb off of the intake and saw a puddle of gas laying on the driver side barrels inide of the intake manifold. The pass side was also very wet but not puddled like the driver side. Looks like the guy that rebuilt the carb for me gave me a royal shaft instead of a rebuild.

I checked the points inside the distributor today and made sure they were adjusted to .016 like the factory service manual says. Everything inside the distributor appeared fine and nothing was loose or broken that I could see. I checked for spark and I was getting spark with a plug going to the valve cover.

I installed the carb that we had on the motor prior to us putting the rebuilt dated numbers matching one back on and now I can not get the engine to fire up. I did not pull out the new plugs yet to see if they were wet as I was running out of time and had to be somewhere. I am going to do some more detective work on it tomorrow to see why the motor is not firing up now.
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Brian
Morris County, NJ

El Camino----The ORIGINAL Sport Utility Vehicle !

-1970 El Camino SS 396 (true SS, highly optioned car) AACA Senior Gold Winner (Hershey 2005) , 2006 Concours d'Elegance Star Award winner
-1969 Dodge Charger HP 383 ci. 4 spd AACA Senior National Winner (Herhey 2007)
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Old Mar 29th, 05, 4:48 PM
Resq302 Resq302 is offline
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Default Re: Causes for backfire through carb???

Don, the firing order and wire routing were exactly as the were back when I put the car away for the winter. The wires are also less than a year old.
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Brian
Morris County, NJ

El Camino----The ORIGINAL Sport Utility Vehicle !

-1970 El Camino SS 396 (true SS, highly optioned car) AACA Senior Gold Winner (Hershey 2005) , 2006 Concours d'Elegance Star Award winner
-1969 Dodge Charger HP 383 ci. 4 spd AACA Senior National Winner (Herhey 2007)
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Old Mar 30th, 05, 12:43 PM
ss3964spd ss3964spd is offline
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Default Re: Causes for backfire through carb???

Brian,

I recall in a previous post you mentioned the carb - and obviously the thing is leaking in a big way - likely the float isn't adjusted right. big bummer to have spent all that money on a restored carb and hvae it not work right. I had exactly the same prob.

As far as it not firing with the new carb - three things: 1st - remember that you'll have to crank it a bit to fill the float bowl(s). 2nd - if the new plugs were that wet you'll need to get them dry - or replace them again. 3rd, since you said you were in the distributor checking the point gap, go back in and make certain both wires (coil and condenser) are still connected to the points. Make sure the center button of the dist cap is in good shape, and the the tab on the rotor is making contact with the center button.

BTW, although the factory spec for the points gap is .016 - which will ensure the engine runs, you really need to check it with a dwell meter. Factory spec for the dwell is 28-32 degrees.

Dan
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Old Mar 30th, 05, 3:09 PM
Resq302 Resq302 is offline
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Lightbulb Re: Causes for backfire through carb???

Hi Dan,

Today with the new carb still on there, I removed the points and filed the contacts down to fresh clean material and regapped them to factory specs. After that, I checked out the cap inside and out for cracks, contamination, etc and that was fine also. Next I doulbe checked the spark plug wires to be sure that someone didnt play around with them without me knowing. They also checked out fine. Onto the spark plugs.... I bought all new R44T spark plugs and installed them after making sure the gapping was correct. Before I installed the #1 plug, I removed the cap off of the distributor and make sure that the piston was at top dead center alligned with the #1 wire on the cap. After making sure that was ok and moving the distributor a bit, I was able to start it up. It sputtered at first but after getting the timing light out and getting it idling correctly, I was able to fine tune it and everything seems fine now. The nice news is that it is not spewing out black smoke like before. I think I will run it a bit and maybe take it out for a test spin to see how it runs and then recheck the timing and mixture. The only thing I am going to have to do now is borrow a friends dwell meter to double check the dwell and make sure that is within spec also but when I give it full throttle from idle (and ducking for cover) it only backfired through the carb once and that was before I had the mixture screws fully adjusted. Lets keep our fingers crossed and see how she makes out. So far so good.

Thanks for everyones input and suggestions as it helped me get through this major headache. Now to send out the numbers matching carb to be rebuilt yet again. Does anyone have any suggestions as to who I should send my carb to??
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Brian
Morris County, NJ

El Camino----The ORIGINAL Sport Utility Vehicle !

-1970 El Camino SS 396 (true SS, highly optioned car) AACA Senior Gold Winner (Hershey 2005) , 2006 Concours d'Elegance Star Award winner
-1969 Dodge Charger HP 383 ci. 4 spd AACA Senior National Winner (Herhey 2007)
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Old Apr 2nd, 05, 11:05 PM
71350SS 71350SS is offline
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Default Re: Causes for backfire through carb???

Brian,
Give Steve a call.
http://www.stevescarb.com/services.htm
I've dealt with him for years they do good work.
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