Popping back in exhaust

[Mr2.4]

Do any of you guys have some suggestions. On Thanksgiving day My dad, nephew and me put a Comp cams 292H in my 340 and also added a LD340 intake. Now the motor won't stop popping. It sounds like M-80's going off in my exhaust. I have adjusted timing like crazy, put in new spark plugs, Checked the gap on the reluctor in the dist., checked my carb for trash. readjusted the air idle screw's, and checked the float level, checked all of the rockers and push rods. All valves appear to be opening flawlessly. I know for a fact that the cam timing is spot on " long story." Any way If you guys can help I would greatly appreciate it.

Motor specs are:
71 340 .060
10.5:1 comp.
J-heads 1.88 valves
Comp cams 292H .501 lift
LD340 Intake
Holley 650 DP
67 primary jets
Can't remember squirter size I think it is 27
Electronic ign.
Hooker Headers.

I will try to get a video loaded so you guy's can hear what I am talkin about.

 

[slant6/4speed]

Quick thought-air leak into the exhaust system or the intake manifold? Did you touch the the exhaust system? Does it pop all the time? trailing throttle? RPM range? Ignition solid and not jumping around??

 

[clhyer]

Did you check your plug wires to make sure you haven't crossed any?
C

 

[demon seed]

An exhaust valve that is being held open will cause raw fuel to go down the exhaust and you'll get a popping sound. The valve only has to be open a tinny amount to get the result. I'd pull all the plugs and do a compression test with the carb wide open.

 

[Mr2.4]

Airleak is something I do need to check. Sparkplug wires have been checked.

 

[AJ71DUSTER]

Not to change post But Mr2.4 pm me and let me know what the neon runs, son has A 05 SRT 4 with a stage 3.

Thanks

 

[green1]

gg

 

[green1]

Cam degreed correct?

 

[packin3deuces]

My 340 6 pack was popping like a 4th of July grand finale a few weeks ago. I replaced the power valve in the center carb and no more fireworks. :happy3:

 

[Mr2.4]

 

[Mr2.4]

I have never used a cam degree wheel. I think it's time to learn. Regardless of this issue. The power valve I had thought about but it's supposed to be the anti blowout type. Could be though crap anything is possible.

 

[chryslerfat]

A vacuum leak can cause this also.

 

[green1]

Cam replaced, and intake. Carb power valve shouldn't have changed, unless backfire through the carb.

 

[Cudafever]

Are you sure you haven't crossed #5 and #7 spark plug wire. its so easy to do!

Is that pop sound through exh system or open headers?......

sounds Loud!!!

 

[Mr2.4]

I made sure the plug wires where right. Heck I even crossed them to make sure and it still does it. The car has headers with about a foot of 2 1/2" pipe to a pair of 2 1/2" glass packs and thats it. Green1 I did have a back fire through the carb when messing with the timing.

 

[Cudafever]

What was the cam lift of the previous cam?

How long was the previous cam, in this eng?

When you broke in the cam, did it pop at a high idle, or does it only pop when you let off the go peddle?

What Carb is setting on top of the LD 340 manifold?


With it only being a single pop, i would suspect a single cylinder............i thing a compression check(as was mention above) is a good starting point to find you problem.

 

[RustyRatRod]

Crossing 5&7 would be my first thought. I've done it and triple checked before and STILL had um crossed. It's REAL easy to do. 1 8 4 3 6 5 7 2.

 

[dustoff440]

check for a partially wiped cam lobe

 

[Demon 408]

Had the same popping in my exhaust after I got my Demon together. Problem was caused by carb float adjustment in the secondaries of the carb (950 Holley DP). When I adjusted the float level down to the correct level it stopped. I can tell by the pop occurring after you get out of the throttle, unburned gas is igniting in the hot exhaust. Also check for pin hole in float causing the float to sink in the bowl and level of gas to rise.

 

[Mr2.4]

Cudafever: The previous cam was a Crane HV272 .454/.480 lift It also had a Edelbrock LD4B intake manifold on it. The motor dosen't pop up high. Only at idle. Once the motor starts warming up it will pop without me giving it gas, and it will do it out both sides of the motor.

Demon408: I will try that and see if that helps. I am begining to think that it is more of a problem with my carb.

StrokerScamp: I'm ahead of you. I already tried, with no such luck. Thanks though.

Dustoff440: Already checked and all of the valves are opening fully.

 

[mopar head]

If all else fails, See if your reluctor pin is still in:clock:

 

[Mr2.4]

If all else fails, See if your reluctor pin is still in:clock:

It is. I accually pulled my dist out yesterday and reset the gap on my reluctor and pickup.

 

[Rob R]

Poping out the ex = 99% of the time it's an ex valve...stick your finger in the plug holes and turn it over.
My guess is it nicked a ex valve...

 

[Demon 408]

I would definitely check carb float adjustments as one of your first options, it's free and it's easy, especially when compared to other options. Hopefully your carb has external float adjustment and clear site plugs like mine, makes it easy to do wet float adjustment. Good luck and keep us updated.

 

[green1]

Just throwing this out there. I once bought a 400 T/A 400, that did the same thing. Machinest said it was carbon built up behind the valves, He was right.