Backfire
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Joined: May 2013
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From: Haysville, KS
Backfire
Took the truck to Lowes today, the longest trip since replacing the distributor and carburetor. Ran fine, but when I shut it off it backfired once. Same thing when I got home.
My brain is a little tired at the moment - thoughts on the cause of the backfire?
I'm thinking maybe too rich (or lean??), maybe timing to retarded (or advanced??)
I can't tel if the backfire was in the exhaust or carburetor. I think it was exhaust but my wife thinks carburetor..
Thoughts??
(brain is tired from home chores.. I installed a whole house humidifier to help with the static electricity. My wife went to turn up the thermostat so we could test the humidifier, and blew up the thermostat when it sparked because of static electricity... How ironic)
My brain is a little tired at the moment - thoughts on the cause of the backfire?
I'm thinking maybe too rich (or lean??), maybe timing to retarded (or advanced??)
I can't tel if the backfire was in the exhaust or carburetor. I think it was exhaust but my wife thinks carburetor..
Thoughts??
(brain is tired from home chores.. I installed a whole house humidifier to help with the static electricity. My wife went to turn up the thermostat so we could test the humidifier, and blew up the thermostat when it sparked because of static electricity... How ironic)
pedant
Joined: Jan 2008
Posts: 23,576
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From: EXTREME southwest CT
I know you have a relay wired to your coil.
But I forget all the details of your DUI ignition mods.
The coil will always fire when the power is disconnected.
Maybe something is backfeeding or otherwise momentarily energizing the coil after you turn the key off?
The truck doesn't seem to be idling high or running on (dieseling) does it?
You just set the timing last week, didn't you?
But I forget all the details of your DUI ignition mods.
The coil will always fire when the power is disconnected.
Maybe something is backfeeding or otherwise momentarily energizing the coil after you turn the key off?
The truck doesn't seem to be idling high or running on (dieseling) does it?
You just set the timing last week, didn't you?
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From: Haysville, KS
I just checked the timing last week and it is at 10 btdc. I doesn't backfire when I shut it off unless it's been running for a bit. I tend to think it's hot exhaust / rich mixture but I'm just guessing at this point.
I suppose I could get out the O2 meter and check the exhaust levels. I might try to get that done tomorrow as the weather is supposed to be nice.
I now have a new problem - see new thread - Parking Lights..
I suppose I could get out the O2 meter and check the exhaust levels. I might try to get that done tomorrow as the weather is supposed to be nice.
I now have a new problem - see new thread - Parking Lights..
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From: Haysville, KS
Could be somehow related. I'm wondering if an exhaust leak (at the old AIR tube) could cause this? I don't know that there is a leak, but you never know. I can get a down tube without the air tube, something I've been considering in any case.
Good thing I like to tinker..
Good thing I like to tinker..
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From: Virginia
If it's in the exhaust, it's unburned fuel lighting off inside the exhaust. This would go along with your theory that it's running too rich.
You might also check where you are feeding the ignition. You said you used a relay, but where is the relay feeding from? I have seen people tie their ignition in along with the alternator regulator, and the regulator will backfeed voltage to the ignition circuit when the key is turned off. You will know if this is the case, when you have this problem the engine will slowly die instead of just cutting off "right now" with the switch. The factory got around this by putting the ignition on it's own part of the ignition switch with it's own set of contacts.
You might also check where you are feeding the ignition. You said you used a relay, but where is the relay feeding from? I have seen people tie their ignition in along with the alternator regulator, and the regulator will backfeed voltage to the ignition circuit when the key is turned off. You will know if this is the case, when you have this problem the engine will slowly die instead of just cutting off "right now" with the switch. The factory got around this by putting the ignition on it's own part of the ignition switch with it's own set of contacts.
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From: Haysville, KS
I have the feed for the ignition relay from the battery as DUI suggested. The 'trigger' for the relay is the old coil hot wire (key on power). Once the key is off, the relay de-energizes and the power is cut to the coil. At least that's the theory and how it tested..
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pedant
Joined: Jan 2008
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From: EXTREME southwest CT
You say you have an O2 meter.
It would be nice if there were an affordable CO meter available.
You have a new carb too right?
Does the truck feel 'fat' while driving it around?
It would be nice if there were an affordable CO meter available.
You have a new carb too right?
Does the truck feel 'fat' while driving it around?
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From: Virginia
If you fed it from the original coil power, you should be good on that. A high idle will also draw a lot of unburnt fuel into the exhaust when you cut the ignition. Most lawnmowers will do the same thing if you kill them with the throttle wide open.
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From: Haysville, KS
Idle seems OK but worth double checking. New carburetor so it might need a bit of tweaking. Truck seems to drive fine, doesn't seem 'fat'.
In terms of the O2 meter, I have the Gunson meter. I know that Auto Meter makes one that works with an O2 sensor for about $80. Now that I think about it, I do have an O2 sensor that isn't being used anymore...
In terms of the O2 meter, I have the Gunson meter. I know that Auto Meter makes one that works with an O2 sensor for about $80. Now that I think about it, I do have an O2 sensor that isn't being used anymore...
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