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Old 07-28-2018, 10:55 AM
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sbc backfire thru carb - stalled and now wont start

Good morning. I have an old bread truck that I converted into a party bus, last summer I swapped the motor (an 82) for and 84 SBC. I was told that the motor came from a hot rod but that it was put back to stock or me. I bought the motor for $500, and then paid a friend friend of a friend of a friend to install it for $500. Shortly after, I had the Edelbrock carburetor rebuilt. And I had the transmission rebuilt.

I'm not a mechanic, but I like to solve problems when I can, because I'm also not a millionaire! The carb has recently started backfiring, so I have been trying to adjust air on the two front screws based on my YouTube university degree in carb and motor repair.

Yesterday the motor ceased to start after backfire and stalling on the street. A friendly gentleman hooked a chain to my party bus and got me off the main road, but I still can't get this bus to start!

I'm going to grab some basic supplies… Carb cleaner, air filter, fuel filter, maybe plugs as well and head back to the truck now. If anybody can give me some insight, I will greatly appreciate it!! Why the backfire, why it won't start?

~Sara
heres my bus...***************m

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Old 07-29-2018, 10:10 AM
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Backfire through carb can be, Timing, not getting enough fuel (lean) not enough spark, but I'm leaning toward timing chain has jumped teeth so check basic timing.
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Old 07-29-2018, 11:26 AM
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You may want to take a small amount of gas and pour some into the carb. If it runs for a short time then it is probably in fuel delivery.
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Old 07-29-2018, 11:47 AM
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Quote:
Originally Posted by azJAMtram View Post
Good morning. I have an old bread truck that I converted into a party bus, last summer I swapped the motor (an 82) for and 84 SBC. I was told that the motor came from a hot rod but that it was put back to stockWhat did they do to put it back to stock?or me. I bought the motor for $500, and then paid a friend friend of a friend of a friend to install itThe install..how did it go?--what was messed with? wiring--ectfor $500. Shortly after, I had the Edelbrock carburetor rebuiltwas the carb rebuilt by someone who knows how to properly do the rebuild? rebuilding carbs isn't my cup of Tea, however they are tedious someone has to know what they are doing to rebuild it correctly. And I had the transmission rebuilt.

I'm not a mechanic, I'm not a mechanic either, but I've worked on a lot of mechanical stuff over the years and love to wernchit---but I like to solve problems when I can, because I'm also not a millionaire! The carb has recently started backfiring, so I have been trying to adjust air on the two front screws based on my YouTube university degree in carb and motor repair.if your getting BF from the carb--- it's a troubleshooting issue now start with the basic checks

Yesterday the motor ceased to start after backfire and stalling on the street. A friendly gentleman hooked a chain to my party bus and got me off the main road, but I still can't get this bus to start!

I'm going to grab some basic supplies… Carb cleaner, air filter, fuel filter, maybe plugs as well and head back to the truck now. If anybody can give me some insight, I will greatly appreciate it!! Why the backfire, why it won't start?

~Sara
heres my bus...***************m
This forum has a lot of folks with good sound knowledge and experience to back it up and are willing to help.
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Old 07-29-2018, 12:41 PM
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Originally Posted by Fang16 View Post
You may want to take a small amount of gas and pour some into the carb. If it runs for a short time then it is probably in fuel delivery.
I'm getting fuel, I set the electric choke to open and disconnected it. I'm going to find someone with a timing gun and check the timing... I'll check dist cap as well.
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Old 07-29-2018, 01:20 PM
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You’re definitely getting fuel!
Likely too much fuel.
Likely flooding.
Edelbrock carbs are notorious for not liking fuel pressure higher than 5 psi.
You might need a fuel regulator to control pressure.
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Old 07-31-2018, 02:49 PM
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Quote:
Originally Posted by RWENUTS View Post
You’re definitely getting fuel!
Likely too much fuel.
Likely flooding.
Edelbrock carbs are notorious for not liking fuel pressure higher than 5 psi.
You might need a fuel regulator to control pressure.
That sounds reasonable. There is a bypassed unit, I don't know if it's a fuel pump or regulator, but it;'s still mounted in the engine compartment... I'll look more into what it is, and if it works or if I need a new one.

thank you!
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Old 07-31-2018, 03:57 PM
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Take a pic of whatever it is and someone here will tell you all about it!
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Old 07-31-2018, 08:06 PM
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[COLOR=#000000]From1982 to 1984 there is little difference between these years. You mentioned that the engine was changedback to “stock”, so the question is what was changed.It could be the engine was already worn outand you are just experiencing its normal diminishing life cycle and the causeand effect of this wear.As othersmentioned, the issue might be timing.Back fire thought the carb is usually the air fuel charge beinginitiated by spark while the flame is able to travel from the cylinder to thecarb via the manifold.[/COLOR]
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On theEdelbrock carb turn the front two screws in all the way and then back them out1.5 turns, your base tune will usually be between 1.5 to 2.5 turns out. On the electric choke loosen the three smallscrews on the choke spring cover and rotate toward the front until the chokeplate closes off the air horn completely. Then back off the other directionuntil you have a base opening about 35 thousands, which is close to a 1/32drill bit (.03125 inch) thickness or use the thickness of a matchbookcover..030 to .035 inch is ok to startwith.With engine running at operatingtemperature the choke plate should be all the way open.On a “cold’ engine the choke needs to beclosed to build the vacuum needed to start the process of pulling the fuel andinto the manifold and etc…The “cold”engine idling process is very inefficient and is designed to run rich.[/COLOR]

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A quickcheck is to do is check to see if the distributor has gotten loose andmoved. The rotor turns clockwise so ifit moved counter clockwise, it will be too much advanced and will back firethrough the carb.If it moved too muchclockwise, it will be retarded and can back fire through exhaust.Next check the obvious and check for vacuumleaks any tubing coming off the carb or manifold.Also check the big tube that goes from theback of the carb to the brake booster.You can remove this and temporary tape this off or use pinch pliers.If you have hydro-boost you won’t have thistube.[/COLOR]

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Take acan of starting fluid (ether) and give the carb about a ½ second shot and tryto start. Does it start and run?Next use about ½ shot glass amount of freshgasoline and pour down the carb, does it start? or does it just back fire?
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If thetiming is right, if the distributor is setup correct, compression is correctand still back firing most likely is spark timing. Another item not mentioned is make sure allthe spark wires are connected correctly.A crossed wire can cause back fire.Also a bad cap or coil or rotor can cause back fire.


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To findout what is going on, you need to find true top dead center on number onepiston. Number one cylinder is the mostforward cylinder on the driver’s side and the firing order is 1-8-4-3-6-5-7-2.See Pic.
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Youwill have to rotate the main crank pulley until it lines up with the timing tabon the front of the engine. You mightneed to get some help but if you can line up the timing mark next pull thedistributor cap and see where the rotor is pointing.It should be pointing to the # 1 tower, so itshould be facing forward and if you think of a clock where the back of thedistributor next to the fire wall as 12:oclock the #1 tower is at the 5:oclockposition
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Watchyouie tubie university on how to do a compression test and do one dry andwet. Write down the numbers andcompare.A wet check is to squirt smallamount 5 CC or so in to the open spark plug hole of the cylinder.If the dry number is low and then the wetnumber is much higher you have severe worn ringsor valves not sealing, or other mechanicalissue.[/COLOR]

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MinimumTools you will need: = ½ inch ratchet or breaker bar, ½ socket for crank bolt,vacuum gage, compressing gage, timing light. Spark plug socket or spark plugremoval kit (3/8 drive, swivel spark plug socket, extension bar, small oil squirtcan, assorted screw drivers, basic tool set, sockets, wrenches etc…[/COLOR]

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See ifyour friend that installed it can help diagnose[/COLOR]

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Last edited by Foperfoauto; 07-31-2018 at 08:09 PM. Reason: typo
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Old 08-01-2018, 02:41 PM
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Quick check -- Pull distributor cap off and make sure the rotor is spinning while someone turns over the engine.
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