Popping through exhaust

[Bob H.]

What sounded like a miss to me at first is apparently afterfire. It is occurring more often at idle. It you hold your hand over the exhaust as it "pops" you feel a puff of air. It is happenig on the driver side only although the car seems to be running rich as all the plugs are black. I checked the fuel level on the center carb and saw it was barely coming out the hole on the side of the carb. When I went to adjust the inlet valve, I found it was turned down all the way, I changed it but found the new valve had to be turned in all the way to. could the float being "on the edge of being too high cause it to run rich?

It smells to high heaven when this occurs. It will run you out of the garage.

[Clem Z.]

Re: Popping through exhaust

What sounded like a miss to me at first is apparently afterfire. It is occurring more often at idle. It you hold your hand over the exhaust as it "pops" you feel a puff of air. It is happenig on the driver side only although the car seems to be running rich as all the plugs are black. I checked the fuel level on the center carb and saw it was barely coming out the hole on the side of the carb. When I went to adjust the inlet valve, I found it was turned down all the way, I changed it but found the new valve had to be turned in all the way to. could the float being "on the edge of being too high cause it to run rich?

It smells to high heaven when this occurs. It will run you out of the garage.

sounds like the float arm is bent.

[Bob H.]

Re: Popping through exhaust

I'll pull it apart tomorrow and check it out

[Gerard F.]

Re: Popping through exhaust

Bob,

I found with my 3810, the secondary float was loose in its pivots, and bent forward to hang up on the metering plate when I braked and came to a stop, or just cruising downhill.

The fix was simply to bend the float back to the back of the bowl with my thumb. Don't bend it too far as then it will hang at the back of the bowl.
With the metering plate sticking into the secondary bowl, you'll see that there is very little clearance either way.

Maybe this is your problem. It solved my over rich problem and the drip drip drip into the secondary bowl.

[Timothy B.]

Re: Popping through exhaust

Bob,

After the car warms can you trim the idle A/F ratio with the curb idle screws on the sides of the metering block.. You should be able to turn these in and kill the motor.

If not then it's getting gas from somewhere else or the primary throttle blades are open to far allowing to much fuel through the transfer slots. What is idle RPM of the engine??

[Bob H.]

Re: Popping through exhaust

Thanks.

Before pulling it off (what a pain) I'll will check the throttle plate . I'll confirm I can kill the engine by adjusting the idle screws but believe I can.

Idle right now is about 700. It is an L71. A bent tab certainly sounds likely but I'll go ahead and change the power valve and do some cleaning while apart.

I did find all three needle and seats would "hang up" at times. Perhaps, our fine ethanol gas. I do have a blend of 93 and 100 in it right now.

[Timothy B.]

Re: Popping through exhaust

Bob,

Also keep in mind as long as the spark plugs are dirty/sooty, the spark may not be consistent, spark will follow the soot path to ground. After repairing the carburetor you may want to clean the plugs by glassbeading.

Take a piece of 220 wet paper and litely sand the bottom and top of the throttle body and main body. Go get a 1/4" thick piece of glass cut 3 3/4" wide and it should fit between in the main body with a piece of sandpaper. Also sand the front of the main body where the metering block goes.

Sometimes the metering blocks are not flat but if the main body is flat a new gasket can fix it. The vacuum can draw fuel out of the idle down well into the engine.

[David S.]

Re: Popping through exhaust

Bob,

Also keep in mind as long as the spark plugs are dirty/sooty, the spark may not be consistent, spark will follow the soot path to ground. After repairing the carburetor you may want to clean the plugs by glassbeading.

Take a piece of 220 wet paper and litely sand the bottom and top of the throttle body and main body. Go get a 1/4" thick piece of glass cut 3 3/4" wide and it should fit between in the main body with a piece of sandpaper. Also sand the front of the main body where the metering block goes.

Sometimes the metering blocks are not flat but if the main body is flat a new gasket can fix it. The vacuum can draw fuel out of the idle down well into the engine.

I think I would replace the plugs before glass-beading them. Just my $.02

I see this thread is in reference to a 67. Does that 67 happen to have a A.I.R. Smog System? If so have the smog pump rebuilt non-functionally. We had a similar problem on a 69 Z28 Camaro. After the smog pump was rebuilt, no more popping.

-Dave

[Timothy B.]

Re: Popping through exhaust

David,

If the spark plugs are carefully covered, it only takes a small amount of air pressure to clean the INSIDE area followed by a good air pressure cleaning. If they are not cracked the plugs will work like new.

My point is that even after correcting the rich condition, the plugs are still dirty and high voltage will take the path of least resistance to ground and that can be the soot path causing poor performance.