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Can loose valves cause occasianal backfires? When i’m on an incline, or turning sharp, and I dont gove it a lot of gas, sometimes a backfire comes through the carb. This just started occuring a couple days ago, and has happened 4 or 5 times. One time it killed the engine. This sucks cuz for the last month or so its been driving perfectly after going through some vacuum and timing issues. Ive checked everything off the list except a valve adjustment. Any ideas?
Backfiring through the carb is usually timing - an intake valve is open when the spark plug fires. A loose rocker would allow the valve spring to close the valve sooner or faster - unless maybe the valve is bent or something and it is not snapping back shut right away.
If you had a valve adjustment issue. It wouldn't raise it's ugly head only on an incline or when turning hard.
Perhaps going lean would. Improper float level adjustment comes to mind.
From: At my Bar drinking and wrenching in Lafayette Colorado
Backfire up through the carb is usually indicative of a lean condition. This can be caused by faulty accel pump system, plugged discharge nozzles, and bad accel pump due to ethanol fuel with a poor quality accel pump.
Lars
Backfiring through the carburator can also be caused by an exhaust valve not opening also, and I hate to use this term, a Crossfire due to a bad distributor cap.
Last edited by Fly skids up!; Dec 24, 2021 at 09:26 AM.
From: At my Bar drinking and wrenching in Lafayette Colorado
If there is a valve problem or a cross-firing distributor cap, the backfire will be regular and constant. He has an "occasional" backfire that can be induced by throttle position, throttle movement, and fuel slosh/fuel level. Everything points to a lean condition induced by some problem with the carb.
Lars
If there is a valve problem or a cross-firing distributor cap, the backfire will be regular and constant. He has an "occasional" backfire that can be induced by throttle position, throttle movement, and fuel slosh/fuel level. Everything points to a lean condition induced by some problem with the carb.
Lars
You left out a low float level....this would rear its head on inclines and turns......
If there is a valve problem or a cross-firing distributor cap, the backfire will be regular and constant. He has an "occasional" backfire that can be induced by throttle position, throttle movement, and fuel slosh/fuel level. Everything points to a lean condition induced by some problem with the carb.
Lars
I got to disagree with that statement. I've seen intermittent back firing problems caused by cams going flat, carbon tracking in the distributor cap, etc. The other thing is what's occasion to the OP is subjective. Occasion to him maybe once every 5 seconds or 5 minutes. I'm sure if anyone of us was actually there to hear the backfire we would immediately know exactly what was going on.
Nothing to do with this but a good example how people think. I got a phone call from someone saying his A/C needed to be recharged. He dropped the car off. I started the car up and turned on the A/C. You could hang meat in that car it was so cold. I called him back and told him A/C is working fine. He said yes but when I put the A/C on the "charge" light would come on. It was just a low idle. I got a million stories like this. Marc
Thanks for the info guys i’ll open the carb up again. I didnt think about the accel pump, thatll be the first thing i look at. I just adjusted my floats to 7/16 and 1 inch a month ago. I’ll double check them too.
From: At my Bar drinking and wrenching in Lafayette Colorado
Originally Posted by Jebbysan
You left out a low float level....this would rear its head on inclines and turns......
Jebby
Jebby -
I actually indicated it was a carb problem with a lean condition - that would include a variety of issues, including low flow, that can induce a lean condition with carb under various conditions. As you know, there are at least a dozen other issues that can also induce a lean condition with resultant backfire up through the carb.
Lars
What in the world type of carb do you have with a 7/16" float level...??
I shouldve clarified in the original post, its an edlebrock 1406. New accep pump didnt change anything, as well as changing the location of the accel linkage to a more agressive fuel load
Backfiring through the carb is usually timing - an intake valve is open when the spark plug fires. A loose rocker would allow the valve spring to close the valve sooner or faster - unless maybe the valve is bent or something and it is not snapping back shut right away.
In addition, a loose rocker can cause the pushrod to bind up and bend. Then the bent rod will affect the valve timing. It is possible but i don't know about the probability of it happening. Plus it would be a consistent missfire. So Lars has it nailed again
Valve adjustment and backfires
