carb problem?

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Doogster

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Carb is making a popping noise when given a quick shot of gas...ie when it's floored. idles fine, and if you achieve high rpms gradually...will hit high rpms smoothly. Starts great as well, and never stalls. i have replaced the plugs, wires, and coil. Timing is fine too. Acts like a vacuum leak, but I can't find it anywhere. This car hasn't been driven in a couple of years, as it was being restored. (ran fine before)

340 solid roller
Edelbrock carb

Two part question, is it the carb? ie dirty perhaps, or stiff from under use? something else?
Secondly, will it harm anything to drive it with the carb popping like that?

thanks!
 
Sounds like a lean backfire. With the engine shut off and the air cleaner removed and wearing safety glasses look down the throat of the carb and push the accelerator. Do you see a stream of gas shooting into each front barrel? If not the accelerator pump has died. Could be just gummed up from setting. Fuel turns to varnish like gunk when it evaporates. Most likely needs taken off, taken apart, cleaned good and new gaskets installed. If it is indeed backfiring through the carb it could catch on fire if driven like that.
 
fishy68 said:
Sounds like a lean backfire. With the engine shut off and the air cleaner removed and wearing safety glasses look down the throat of the carb and push the accelerator. Do you see a stream of gas shooting into each front barrel? If not the accelerator pump has died. Could be just gummed up from setting. Fuel turns to varnish like gunk when it evaporates. Most likely needs taken off, taken apart, cleaned good and new gaskets installed. If it is indeed backfiring through the carb it could catch on fire if driven like that.
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Already checked that...fuel shoots ito the barrels fine. Already took the carb off and cleaned it and blew it out good. Could the gasket be the problem?
 
Doogster said:
Already checked that...fuel shoots ito the barrels fine. Already took the carb off and cleaned it and blew it out good. Could the gasket be the problem?
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Yeah if it's sucking air real bad. Only thing is carb. base gaskets (I assume that's the one your referring to) generally don't go bad after setting just a couple yrs. When you had the carb apart did you check/adjust the float levels? Also, when you say the timing is fine how did you verify that? Did you have the vacuum advance (if so equipped) unhooked and plugged?
 
it pops regardless of where the timing is set. it ran perfect before it went to the body shop. no lifter noise either, and the vacuum advance is plugged. I didn't adjust the float levels, just took it off...and blew it out with compressed air, thinking that there may have been some dirt in it.
Could it be the plunger not pushing enough fuel through under quick acceleration? it only pops when it's given that quick shot of gas.
 
Doogster said:
it pops regardless of where the timing is set. it ran perfect before it went to the body shop. no lifter noise either, and the vacuum advance is plugged. I didn't adjust the float levels, just took it off...and blew it out with compressed air, thinking that there may have been some dirt in it.
Could it be the plunger not pushing enough fuel through under quick acceleration? it only pops when it's given that quick shot of gas.
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That's a possibility. Does the accelerator pump arm have 3 holes in it where you hook up the linkage? If so what hole is it in? The hole nearest the top of the carb gives the most pump shot. If it's not in that hole try it there and also check it to make sure nothing binds up when you change it to that hole and look down the barrel again to make sure it shoots fuel immediately upon moving the accelerator and throughout the complete cycle. If that doesn't do it it may just be lean in the main circuit. Do you have any jets and/or metering rods to try enrichening it?

BTW: I asked about the float levels because every Eddy I've taken apart has had mis-adjusted floats. Mis-adjusted floats (set low) can make it run lean.
 
inertia said:
any lifter noise, if so, possibly stuck exhaust valve, or stuck valve AND bent pushrod..
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Excactly my guess seen it many times. Consistant pop from an exhaust valve not opening and the fired charge is being sent back up through the intake causing a pop. Check lift on all rockers. Make sure all valves are also closing.
 
Oldmanmopar said:
Excactly my guess seen it many times. Consistant pop from an exhaust valve not opening and the fired charge is being sent back up through the intake causing a pop. Check lift on all rockers. Make sure all valves are also closing.
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I checked them..and they all look like they are working properly...if one is sticking a bit .....how would I tell? And more importantly...how do I fix it?
 
Doogster said:
I tried all 3 holes....makes no difference..how do I adjust the float levels?
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The float level is the space between the float and the bottom of the top housing when the housing is turned upside down. There should be a 3/8" gap there. You bend the float arm to get the desired float level. I use a 3/8" drill bit to verify the gap.
 
Ok I guess we need to clarify something. Is this just a single pop that happens when you floor it or does it just keep popping all the time while you have the accelerator pushed down? It was my understanding by your previous responses that it was just one single pop that happened if you floor it fast. If it keeps popping it's probably a valve train issue.
 
if it the single pop lean condition...you might want to increase the size of the squirter hole....more gas...
 
there probally is a way to test the pickupcoil but i dont know for sure they are only 25 bucks or so and a new one would not hurt anyway i fixed a few cars with this same prob with a new pu coil set bit about 24 thousand i hope this helps
 
it's a continuous pop. if it were a valve problem...wouldn't it pop at idle and higher rpms? it only makes the popping noise if the throttle is opened quickly.
 
Doogster said:
it's a continuous pop. if it were a valve problem...wouldn't it pop at idle and higher rpms? it only makes the popping noise if the throttle is opened quickly.
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If it pops continuously it's likely a valve train issue and the reason you don't hear it at idle is the carb blades are shut muffling it. Not sure what to say on why your not hearing it if you accelerate slowly. Back in the early 80's I replaced a lot of cams on 305 Chevy's that had the soft cam issue. That's the way they acted when a lobe went flat but any time a valve is stuck shut it will do that.
 
Doogster said:
so what's the best way to fix it? and can it be driven?
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If it's a valvetrain problem I wouldn't even start it much less drive it until I found out what the problem is but lets back up here a minute because I just remembered something, you said it's a solid roller cam. It's possible, but unlikely it has a lobe gone flat and if you hear no valvetrain noise that's another sign it may not be valvetrain related. Have you verified it isn't something real simple like a couple plug wires are switched around? What about the dist. cap? Have you looked it over good to make sure it isn't cracked or corroded up? Also check the reluctor to pickup gap in the dist. It should be approx. .008~.012" and spin the engine around and check it on all points, not just one. I have saw a few cases where the dist. shaft was bent and the gap was fine on one side but when you rotated the dist. it either closed up or opened way up on the other side of the reluctor.
 
I changed the oil today...and there was a fair bit of gas in it...which leads me back to thinking it's a carb problem. This is so frustrating! I wanted it to be running correctly before I put it up for the winter.
 
It's possible but fuel in the oil is most likely from a leaking diaphragm on the fuel pump, if you have a mechanical pump. A carb has to be flooding pretty bad to put fuel in the oil. I doubt it'd run if it was flooding bad enough to put fuel in the oil.
 
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