What Causes Carb Backfires?
Thread Starter
Melting Slicks
Joined: Apr 2000
Posts: 2,145
Likes: 1
From: Ft. Walton Beach, Fl USA
What Causes Carb Backfires?
I'm having a heck of a time getting this motor fired up properly. When it fires it'll run for 1-4 seconds, die down, then comeback up. It'll do that for a couple of cycles then it dies with a carb belch. I'm starting to think the dist. is a tooth or so off. I had a little fire. Luckily I have several fire extinguishers in my garage. The first one malfunctioned.
Anyway, does this sound like a valve timing issue? This is the position of the rotor when I installed the dist. It was on the compression stroke at TDC.
Anyway, does this sound like a valve timing issue? This is the position of the rotor when I installed the dist. It was on the compression stroke at TDC.
Safety Car
Joined: Oct 2004
Posts: 3,725
Likes: 5
From: Minnesota
If you're distributor is set to fire at TDC with no advance you'll get backfires. Turn the distributor counterclockwise a little and try again.
You'll probably end up moving over one more cog to get the timing where it should be and have it oriented about where you have it now.
You'll probably end up moving over one more cog to get the timing where it should be and have it oriented about where you have it now.
Team Owner
Joined: Jul 2001
Posts: 182,997
Likes: 88
From: Lakeland, FL
Cruise-In IV-V-VI-VII-VIII Veteran
St. Jude Donor '03, '06, '17
sounds like a timing issue... Like I posted in the other thread.. I lined up #1 with the rotor and had the timing mark at zero.. and it still didn't run right and would backfire through the carb...
Try moving the distributor far to the right, try and if that doesn't work, move it far to the right and try again.. That way I was able to set the timing but the distributor ended up in an unusual angle, so I pulled it and installed it 1 tooth off and I finally had the distributor sitting straight when the timing was set to 36 degrees...
Try moving the distributor far to the right, try and if that doesn't work, move it far to the right and try again.. That way I was able to set the timing but the distributor ended up in an unusual angle, so I pulled it and installed it 1 tooth off and I finally had the distributor sitting straight when the timing was set to 36 degrees...
Thread Starter
Melting Slicks
Joined: Apr 2000
Posts: 2,145
Likes: 1
From: Ft. Walton Beach, Fl USA
Originally Posted by 68-427
Hi
Do you think you could have gotten some condensation in your gas while it was sitting up? I had a simular problem and had to replace the plugs and power valves before it would run.
Rog
Do you think you could have gotten some condensation in your gas while it was sitting up? I had a simular problem and had to replace the plugs and power valves before it would run.
Rog
Thread Starter
Melting Slicks
Joined: Apr 2000
Posts: 2,145
Likes: 1
From: Ft. Walton Beach, Fl USA
Originally Posted by jdmick
If you're distributor is set to fire at TDC with no advance you'll get backfires. Turn the distributor counterclockwise a little and try again.
You'll probably end up moving over one more cog to get the timing where it should be and have it oriented about where you have it now.
You'll probably end up moving over one more cog to get the timing where it should be and have it oriented about where you have it now.
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Thread Starter
Melting Slicks
Joined: Apr 2000
Posts: 2,145
Likes: 1
From: Ft. Walton Beach, Fl USA
Originally Posted by captainmorgan
Are you sure that you have the plug wires on correct. Check your firing order 1-8-4-3-6-5-7-2 and be sure.
Thread Starter
Melting Slicks
Joined: Apr 2000
Posts: 2,145
Likes: 1
From: Ft. Walton Beach, Fl USA
Originally Posted by GrandSportC3
sounds like a timing issue... Like I posted in the other thread.. I lined up #1 with the rotor and had the timing mark at zero.. and it still didn't run right and would backfire through the carb...
Try moving the distributor far to the right, try and if that doesn't work, move it far to the right and try again.. That way I was able to set the timing but the distributor ended up in an unusual angle, so I pulled it and installed it 1 tooth off and I finally had the distributor sitting straight when the timing was set to 36 degrees...
Try moving the distributor far to the right, try and if that doesn't work, move it far to the right and try again.. That way I was able to set the timing but the distributor ended up in an unusual angle, so I pulled it and installed it 1 tooth off and I finally had the distributor sitting straight when the timing was set to 36 degrees...
Le Mans Master
Joined: Mar 2001
Posts: 6,231
Likes: 1,009
From: Watkinsville, GA and Glen Cove, NY
It does sound like a timing thing but you also should check the floats on your carb. I had a similar problem when installing a new carb and found the primary float way low.
Melting Slicks
Joined: Dec 2000
Posts: 2,635
Likes: 0
From: Union Ontario
I'd say you have a timing issue with possibly a couple of sparkplugs mis placed.
Put the engine back up to TDC on #1 and retime it from there. Start at the start don't try and adjust it until it works. IN the end it is usually quicker this way.
When I fired my eninge up today, I had to move the dist 1 tooth just because I couldn't adjust it enough to get good timing.... I didn't have any back fires. Back fires means your timing is way off or you sparkplugs are not located right.
Put the engine back up to TDC on #1 and retime it from there. Start at the start don't try and adjust it until it works. IN the end it is usually quicker this way.
When I fired my eninge up today, I had to move the dist 1 tooth just because I couldn't adjust it enough to get good timing.... I didn't have any back fires. Back fires means your timing is way off or you sparkplugs are not located right.
Race Director
Joined: Nov 2000
Posts: 11,872
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From: Waterloo ontario Canada
Advance the distributor until the engine is hard to turn over then back it off a touch. A retarted ignition will backfire through the carb.
Our distributors turn clockwise to to advance it turn the housing counterclockwise.
Our distributors turn clockwise to to advance it turn the housing counterclockwise.
Team Owner
Joined: Apr 1999
Posts: 21,953
Likes: 1,444
From: Reno Nevada
2024 C3 of the Year Finalist- Modified
With your valve cover off. See the number one cylinder go through an event. Compression stroke. Your just bumping it over with the starter. Then look at the timing indicator. + or - 10 degrees on the damper is no big deal.
Now no matter where the plugs wires are on the dist. before. Set #1.............8 in correct order That way your right in sequence.
+ or - 20 degrees is not abig deal. It will fire up and then dial it in with a timing light
Now no matter where the plugs wires are on the dist. before. Set #1.............8 in correct order That way your right in sequence.
+ or - 20 degrees is not abig deal. It will fire up and then dial it in with a timing light
Thread Starter
Melting Slicks
Joined: Apr 2000
Posts: 2,145
Likes: 1
From: Ft. Walton Beach, Fl USA
Originally Posted by 69ttop502
It does sound like a timing thing but you also should check the floats on your carb. I had a similar problem when installing a new carb and found the primary float way low.
Team Owner
Joined: Jul 2001
Posts: 182,997
Likes: 88
From: Lakeland, FL
Cruise-In IV-V-VI-VII-VIII Veteran
St. Jude Donor '03, '06, '17
Question: Did you change the distributor gear to a bronze gear before installing the distributor?? If you did, did you line up the dimple with the rotor? I just found out that the dimple has to line up or the timing will be off.. If you didn't change it, disregard, otherwise check my distributor gear thraed..
