Why does carburetor pop

The cause: The alternator was "throwing" voltage spikes onto the primary and causing the trigger diode in the electronic ignition module to fire the coil!

A reman alternator cured the problem. After 74 years in auto repair shop you would think I had seen it all! If everything's smooth until you open the throttle, then the accel pump might not be putting that extra squirt into the air stream through the carb. Absent the squirt, the mixture would be too lean, momentarily. With the engine stopped, open the throttle from idle and check for the pump discharge from the accel pump nozzle in the carb throat.

If the mixture is too lean at higher rpm, causing a pop then, it might be that the spark plug or point gap is not agreeable to the coil output capabilities. As the load on the ignition system increases with cylinder pressure at higher rpms and engine load, more propensity for misfires.

Also, worst problem of this type I ever encountered was my Dad's ish motor home. Dad was SURE it was the carb. Did the carb, same result. After doing electrical tune-up points, plugs, cap, condensor, dwell, timing same issue. Issue resolved. One of the carbon "wires" had an air gap in the carbon. Acted as a capacitor, which discharged and caused a loud pop through the carb under acceleration.

A solved issue helps us all learn. This old truck is a points ignition, BUT, I was experiencing huge jumps on the amp gauge when the regulator kicked in. I had another used regulator on the shelf and that seemed to settle it down. While it is more likely to be something else causing the backfire, like the distributor cap. Having good spark plugs gives you the best ignition, making your vehicle run much better. The opposite problem can lead to the same result. Yet again, leftover fuel vapor will flow into the exhaust and could combust there in a backfire.

This can also be caused by a extremely lean condition. Begin typing your search term above and press enter to search. Press ESC to cancel. Joined: Feb 6, Posts: 1, Profile Page. My guess is a mis-adjusted valve. An idle mixture is lean and requires quite a bit of advance to run properly at idle and low speeds. Are you running vacuum advance? C9 , Apr 23, Joined: Jul 9, Posts: Profile Page. Are you using Ethanol? Joined: Mar 3, Posts: 1, Profile Page. Same problem a few cars back, flattened cam lobe.

Fix was new cam and lifters and thorough cleanout of sump. Joined: Jul 6, Posts: 2, Profile Page. The fact that at speed it runs fine leads me to belive it could be a idle air bleed stopped up with debris as this makes for a very lean condition, just my two cents. Joined: Jul 18, Posts: Profile Page. Could be a vac leak making a cyl or two run lean. I would still check timing, ignition, points, etc. Joined: Dec 11, Posts: 3, Profile Page.

I have just the opposite problem. I bought a new crate motor and broke the cam in on an engine test stand before installing it in my coupe. It ran fine with no apparent problems. Now after it warms up I get a strong popping out the exhaust from my left bank.

I changed the fuel to make sure it was fresh and no ethanol. Since nothing was changed inside the carb though how could this happen?? Quote: Since nothing was changed inside the carb though how could this happen??

Holler how things go. I've had regular ECU's act like a popcorn machine when they went bad. Quote: The basics of combustion are that the intake tract flows into the motor and the exhaust flows out. Exhaust lobe wore off cam. I love the smell of Deer guts in the morning, it smells like Check the inside of the distributor cap for carbon tracks. I have seen that happen before. Quote: Check the inside of the distributor cap for carbon tracks. Just checked and the distrubiter cap and it looks good.

Things i did before this problem happended. I took my TTI headers and sent them out to be recoated and then reinstlaled them as well as putting in those Accell shorty header plugs.

Quote: Quote: Check the inside of the distributor cap for carbon tracks. Can't use that accel plug, it don't have enough reach. The plug it's self is not any shorter where it count's for header clearance. Quote: [ Can't use that accel plug, it don't have enough reach.

Well they are working, but you think that be the issue?? Plugs are cheap so what do you all like to run?? They improve throttle response and fuel economy and reduce fouling. Their purified Alumina insulator prevents arcing, and their machine-rolled threads protect heads.

Accel probably makes the right plug for your heads, just the one's you showed won't work for long. Plus that short reach will allow your spark plug threads in your heads to get burned up.

Get the right accell plug with the correct reach so the tip of the plug is where it belongs. If the plugs you installed were hotter than the ones you removed that will also amplify a lean condition. I hate to mention it but the last time I had this problem it was a cam lobe on an exhaust valve.

Stu, is there a reason you took down the picture of the 2 plugs? Sure sounds like a cam lobe BTDT not fun or cheap Good luck and let us know what ya find.

Quote: Stu, is there a reason you took down the picture of the 2 plugs? Yes that was just a stock photo and not indicitve of the one's i have. Here are my plugs as i just pulled them to check the condition so far. They seem to be fine but then they only have about miles on them all so far. JPG downloads. Not just tight by hand with a ratchet sometimes the stupidest things You just had a little surgery with the header change , something didnt go back together right.

Just my two cents but, If my car was running well and I did a few things to it and it started running like crap, I would look really hard at what I did to make sure it was right and possibly start reversing things to see if it cleared up. Quote: Just my two cents but, If my car was running well and I did a few things to it and it started running like crap, I would look really hard at what I did to make sure it was right and possibly start reversing things to see if it cleared up.

Arno You know it's not running bad it runs just fine except for that popping at low RPMs. That's why it hard to diagnose, im going to try new plugs first and see if that helps?? Quote: Quote: Just my two cents but, If my car was running well and I did a few things to it and it started running like crap, I would look really hard at what I did to make sure it was right and possibly start reversing things to see if it cleared up. Thats what I would do. Change back one at a time what you can to see if that makes the difference.

Sorta unrelated but here goes: Last year I installed a Gear Vendors overdrive unit. To get it to fit, I had to cut out the exhaust crossover pipe. The engine sits in the car a bit out of level, so I tried to clock it after loosening the motor mount nuts. I laid a 2 foot level across the valve covers, but I had to spin the distributor a few degrees because the vacuum can was in the way The car ran terrible and was really slow turning over.

I pulled over about a mile after leaving and clocked the distributor until the car ran like before. That wasn't all though. I had also removed the valve cover breather. What the heck was tha Oh, I know what it was The point is, it was good advice from the guy who suggested to try looking at the changes you made. Are you sure those are the correct style plugs for your heads, they look awfully short to me? My heads take a long reach plug. Then use just a drop or two of motor oil on the the threads, no anti seize, imo.

Good luck to you! Quote: Are you sure those are the correct style plugs for your heads, they look awfully short to me? Stock heads like Stu runs take short reach plugs, Edelbrock's take long reach plugs.. Small blocks take long reach Quote: Quote: Are you sure those are the correct style plugs for your heads, they look awfully short to me? The 70 Mag in my Power Wagon did the same thing. The other guys like Randy, who're a lot more mechanic savy than me, might chime in about burnt valves causing the popping.

I will get a new set of regular plugs and see what happens when i install them without the anti sieze on the theads. Maybe these shortie plugs are to blame for the problem?? Personally i think it's an issue with fuel loading up in the carb due to the transmission getting into overdrive too quickly.

I say this as if i shift manually and stay out of overdrive untill over RPM the problem does not happen. I can stand on it and let the transmission shift automaticly and no popping issue all the way to redline Try a set of NGK plugs. I run them in my aluminum headed with I also dont care for Accel wires.

I run Taylors on everything. Mine with 2 inch TTIS have been on at least 12 years. He runs my old worked s with NGK plugs. You migh also have a valve thats just barely burnt. Compression test would tell. Also to check timing chain.

Turn crank to zero. Then while someone watches manually turn it back till the dist moves moves. I like to see less than 10 degrees on an old chain. A burnt valve wouldn't cause popping through the carb. Exhaust valves are the ones that get burnt.

It only backfired thru the tail pipe a couple of times when first starting up. I had A and it did that because it rounded a cam lobe off. Put in the new plugs and it fired up nicely and sounds a little better. I will take a test run tomorrow and see if the new plugs did any good? Quote: I will take a test run tomorrow I can hardly wait. Quote: Quote: I will take a test run tomorrow I can hardly wait You and me both.

Quote: Put in the new plugs and it fired up nicely and sounds a little better. Did california fall off into the ocean, and "tomorrow" never came?

I was going to say that I had popping through the carb on the that was in my car.