Started last week, at idle started to backfire thru the sidepipes. If I get on it it will accelerate, however if I slowly press the pedal it will pop intermitently.
When this happened the last time I changed the plugs and it went away until now, about two weeks.
My car is running rich anyway.
Could this be a result of too much fuel, maybe a bad fuel filter or something with the ignition system??

did you ever get your valve seal problem fixed ??

this problem usually involves timing, carb adjustment or sticking valve.

since you think its ignition related...

have you checked the cap and rotor lately.. how about the plug wires..

you could have a fouled plug already from the valve seal leak..

I would suggest that when you replace the valve seals that you take it slow.. pull the heads, check the valves, time the car properly and adjust the carb properly.

until you get your fairly detrimental problem fixed... ie oil fouling out plugs... your just chasing your tail

Could be all of the above and more, a lean condition causes a backfire through the carb,a rich cond.through the exhaust,but with a blower that could change things,you said it got better when you changed the plugs for a while,what do the plugs look like,what ign.,blower,plugs do you have, did the problem come on suddenley or slowley,does the car actually run good at idle and at speed but pop through the exh, a leaky exh. system will make it pop through the exhaust, need more info.

|UPDATED|6/22/2004 9:35:33 PM (AZT)|/UPDATED|

Exhaust backfire will result from too much fuel in the exhaust. It mixes with oxygen and the heat causes the bang. The fuel can come from rich condition or a misfire. The oxygen can come from a leak, left over in the cylinder from a misfire, or just an air exhange from exhaust vacuum pulses. Common on rich conditions and large short pipes. But cureable.

I notice something similar on mine but only when I downshift or if I'm cruising along and take my foot off the accelerator. I get this frequent "popping" sound out the side pipes - particularly on one side. As soon as I put my foot lightly on the gas, it stops.

Is this still a "too rich" condition of excess fuel in the exhaust?

read an interesting article about blocking off the power valve in a holley ( which has been done in mine ). If you do not increase the main jets by at least 6 sizes you will get an overly rich condition ( which I have ).
I am assuming that changing the jets is not a big deal, if this is my issue regarding my overly rich mixture where can I purchase the larger size jets and are the number of the jets on each one so I know how many sizes to step it up??

Hello,
I know that this might seem silly but have you checked your firing order at your spark plugs?

Recently I was working on my engine and accidently swapped #8 and #4 by accident. They are side by side and it is very easy to do.

With the plug wires reveresed the engine ran but there was popping in the exhaust of the right side of the engine when you just started to press the accelerator (it was heard at the right exhaust pipe on a true dual exhaust with no crossover).

The firing order for the V-8's on Chevys like my 427 is supposed to be 1-8-4-3-6-5-7-2. Start at the #1 cylinder and go clockwise facing down on the top of the distributor. #1 is usually about the One-O'Clock position facing forward from the windshield.

Look for the simplest things first......

I wish you the best of luck!

Chris McCloskey

Any speed shop should have all the jets you need, yes they are numbered,I was wondering why the power valves were removed, for most street-strip applications they should be in there, if you have a rich condition now and you jet up six sizes its going to make it worse, maybe someone has done that already and has gone to far,just guessing but if it were me I think I"d put the power valves back in with the jets that came with the carbs originaly and jet from there.

And backfire on decell is normal. Whey the throttle is closed on decell the fast turning engine draws a lot of vacuum, higher than idle. The high vacuum can't get air past the closed throttle, so it pulls more fuel, and the car goes rich on decell. Very normal. All carb cars do this.
The large exhaust allows air to mix with the exhaust while hot, and the air fuel ignites. Backfire on decell. You can hear racers doing this quite often.