Inform me on backfires
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Cargo Master
Joined: Mar 2014
Posts: 2,031
Likes: 72
Inform me on backfires
First the truck is still running nicely. Plenty of power, idles OK, accelerates smoothly.
Today, driving back from work running about 45 in second, I thought I hit something or was shot at. It was a heck of loud backfire. Pulled over to see what I hit. Truck started idling a little slower and rougher at that point.
Continued down the road and got up to 60 and no issues. Left a stop light and somewhere it had two or three backfires. After the next traffic light, another one of those gunshot sound backfires.
Pulled into home depot. It was idling a little rough.
Picked up what I needed and drove it without incident. Idle was good. No backfire.
At least two of those backfires were loud, very loud.
Now, I have a new rebuilt carb sitting in front of me and will probably go ahead and install it even though most of the issues I was experiencing have faded away - all except the rough start after warming up. I have to hold accelerator to the floor while starting it. First start of the day - full choke and easy start.
Today, driving back from work running about 45 in second, I thought I hit something or was shot at. It was a heck of loud backfire. Pulled over to see what I hit. Truck started idling a little slower and rougher at that point.
Continued down the road and got up to 60 and no issues. Left a stop light and somewhere it had two or three backfires. After the next traffic light, another one of those gunshot sound backfires.
Pulled into home depot. It was idling a little rough.
Picked up what I needed and drove it without incident. Idle was good. No backfire.
At least two of those backfires were loud, very loud.
Now, I have a new rebuilt carb sitting in front of me and will probably go ahead and install it even though most of the issues I was experiencing have faded away - all except the rough start after warming up. I have to hold accelerator to the floor while starting it. First start of the day - full choke and easy start.
Thread Starter
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Cargo Master
Joined: Mar 2014
Posts: 2,031
Likes: 72
240-I6;
3-spd light duty;
Carter YF one-barrel;
points/condenser.
My initial thoughts are this. The lower throttle body return spring is weak and does not return the throttle body as it should (always) be and is contributing to a rich condition. That is providing fuel for the backfires. But I know nothing about this, so I am kind of guessing here.
Lead Driver
Joined: Jul 2009
Posts: 6,477
Likes: 19
From: Sheffield, AL
Check your point gap. I was reminded of an incident which happened years ago. I was stopped at a Cracker Barrel and was in the parking lot. A man was looking under the hood of a 1966 Mustang and had a worried look. I spoke to him and he explained that he was driving down the interstate and hit a bump [expansion joint?] in the road which really jarred the car. Almost immediately, the engine began to run poorly. The points plate had not been tightened securely and when the car was bumped, the point gap closed almost completely.
Since neither of us had a feeler gauge, I used a credit card to set the points and snugged the screws holding the points adjustment plate. You should have seen the look on his face when the engine roared to life! He offered to pay me, but I was reminded of what a friend said to me: "sometimes we do these kind of things for free, just to pay the rent for living here [God's good Earth]"!
Since neither of us had a feeler gauge, I used a credit card to set the points and snugged the screws holding the points adjustment plate. You should have seen the look on his face when the engine roared to life! He offered to pay me, but I was reminded of what a friend said to me: "sometimes we do these kind of things for free, just to pay the rent for living here [God's good Earth]"!
Tuned
Joined: Dec 2001
Posts: 431
Likes: 3
From: Saskatoon sk
Take the distributor cap off and see if the rotor broke and is cocked off straight, or distributor cap is cracked and moisture is causing the spark to wander.
Had a distributor shaft move upwards ( on the way out ) and caused your symptoms.
Had a distributor shaft move upwards ( on the way out ) and caused your symptoms.
Last edited by Paso1; Oct 29, 2014 at 02:00 PM. Reason: spelling
Thread Starter
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Cargo Master
Joined: Mar 2014
Posts: 2,031
Likes: 72
Got to work on it this afternoon.
Distributor, rotor are all in good shape.
Went ahead and replaced the carb with my rebuilt one from Rock Auto. Initially removed a spacer that was with it when I got the truck and just used the gasket. At idle, the engine kind of pulsed and upon acceleration sounded like the exhaust was gurgling. Did not have my vacuum gauge, so tried adjusting the timing by ear. Could not get it to improve much.
Put the spacer back on. Engine behaved a lot better at idle. Think it could be better. Not a super smooth idle, perhaps too slow. It accelerated well. Did not diesel upon shutdown.
Going to put the vacuum gauge on it this weekend see if I can improve it.
Definitely no backfiring.
Distributor, rotor are all in good shape.
Went ahead and replaced the carb with my rebuilt one from Rock Auto. Initially removed a spacer that was with it when I got the truck and just used the gasket. At idle, the engine kind of pulsed and upon acceleration sounded like the exhaust was gurgling. Did not have my vacuum gauge, so tried adjusting the timing by ear. Could not get it to improve much.
Put the spacer back on. Engine behaved a lot better at idle. Think it could be better. Not a super smooth idle, perhaps too slow. It accelerated well. Did not diesel upon shutdown.
Going to put the vacuum gauge on it this weekend see if I can improve it.
Definitely no backfiring.
Postmaster
Joined: Nov 2012
Posts: 2,806
Likes: 8
From: Langley, BC
Backfires happen when the engine is running lean. The mixture doesn't ignite in the cylinder, so it gets passed through to the hot exhaust which then lights it off, so you're literally getting an explosion in your exhaust.
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