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Old 03-20-2012, 02:00 PM
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Have a slight popping noise coming out of my headers on my Southern Sportmod.

Have a popping noise coming out of my headers. Got a new 350 short block, rebuilt 441 heads with comp springs, Insky valves, 10 degree retainers, new cam .480/.480 lift, 245/245 duration (solid lift cam), new comp solid lifters, new MSD dist., new MSD plug wires, new Keith Dorton 500 cfm 2 barrell carb, timing is set a 36 degrees, valves are set at 16 lash all the way across, new NGK 5670-8 spark plugs set at 45. Popping starts at about 2500 rpms. I am also running 1.6 roller tip rocker arms with stock length pushrods. I run 93 octane regular pump gas with some lead additive. Have all new wiring in dash and new gauges and tach. I have been working on this motor for days trying to get the popping out. I thought it was my headers but, tighten all the bolts and still no change. I ran my valves twice after running the motor and when motor was cold. I am starting to think it is my cam.

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Old 03-20-2012, 02:53 PM
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Quote:
Originally Posted by leonmcbee53
Have a popping noise coming out of my headers. Got a new 350 short block, rebuilt 441 heads with comp springs, Insky valves, 10 degree retainers, new cam .480/.480 lift, 245/245 duration (solid lift cam), new comp solid lifters, new MSD dist., new MSD plug wires, new Keith Dorton 500 cfm 2 barrell carb, timing is set a 36 degrees, valves are set at 16 lash all the way across, new NGK 5670-8 spark plugs set at 45. Popping starts at about 2500 rpms. I am also running 1.6 roller tip rocker arms with stock length pushrods. I run 93 octane regular pump gas with some lead additive. Have all new wiring in dash and new gauges and tach. I have been working on this motor for days trying to get the popping out. I thought it was my headers but, tighten all the bolts and still no change. I ran my valves twice after running the motor and when motor was cold. I am starting to think it is my cam.
Both headers? or just one? Could be cam, but I think that would only pop on one side. Have you taken it down the road? Both headers could be lean.
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Old 03-20-2012, 03:39 PM
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Originally Posted by Richiehd
Both headers? or just one? Could be cam, but I think that would only pop on one side. Have you taken it down the road? Both headers could be lean.
X2 popping because its running lean isn't uncommon.
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Old 03-21-2012, 08:36 AM
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Originally Posted by ap72
X2 popping because its running lean isn't uncommon.
Raced it last friday and it would start popping about 3/4 of the way down the straightaway. I had the wrong power valve in the carb. The motor smells like it might be running alittle rich at a idle now. I found two vacuum leaks last night around the intake and carb base. I fix them and still have a slight popping noise. I noticed the tach is jumping around too. It sounds like it is coming from both headers. I have short pipes on the ends of my headers I wonder if that might be causing the popping noise too.
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Old 03-21-2012, 08:59 AM
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Quote:
Originally Posted by leonmcbee53
Raced it last friday and it would start popping about 3/4 of the way down the straightaway. I had the wrong power valve in the carb. The motor smells like it might be running alittle rich at a idle now. I found two vacuum leaks last night around the intake and carb base. I fix them and still have a slight popping noise. I noticed the tach is jumping around too. It sounds like it is coming from both headers. I have short pipes on the ends of my headers I wonder if that might be causing the popping noise too.
If your tach is jumping its likely a faulty module, what ignition module do you have? It may be causing the misfire (popping) or that may still be fuel related. If you have a super lean condition it ma smell rich as it won't fire consistently and the unburned fuel will collect and then burn with a "rich smell". Fix the ignition first, then work on your fuel. a PV should NOT affect idle. Also, if you had 2 leaks, you may have a few more...
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Old 03-21-2012, 10:16 AM
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Quote:
Originally Posted by ap72
If your tach is jumping its likely a faulty module, what ignition module do you have? It may be causing the misfire (popping) or that may still be fuel related. If you have a super lean condition it ma smell rich as it won't fire consistently and the unburned fuel will collect and then burn with a "rich smell". Fix the ignition first, then work on your fuel. a PV should NOT affect idle. Also, if you had 2 leaks, you may have a few more...
I have a MSD board type module with a rev limiter in it. I ran a compression test on cylinders thinking it might have a head gasket leak too But, I did not find anything wrong. I will check for more vacuum leaks. I ran a 10 gauge wire from my battery to the distributer thinking I had a wiring problem in the dash. I advance my crank 2 degrees to get more torque when I put motor together. I have never done that before.
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Old 03-21-2012, 10:25 AM
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you can't advance a crank, do you mean cam? What MSD module do you have? What is your timing set at? Are you running a vac advance can on your distributor? If so what can? Was this carb built specifically for you, or purchased as new shelf stock or purchased used?
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Old 03-21-2012, 12:13 PM
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The last time I watched sportmods race they were ALL popping about halfway down the chute. The stock cars were doing the same thing. This was in hot laps and heat races. By the time they ran the features the track was shiny and black and no more popping. I assumed it was the rev limiters causing the popping.
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Old 03-21-2012, 02:25 PM
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Quote:
Originally Posted by ap72
you can't advance a crank, do you mean cam? What MSD module do you have? What is your timing set at? Are you running a vac advance can on your distributor? If so what can? Was this carb built specifically for you, or purchased as new shelf stock or purchased used?
I mint the cam. I have a 10,000 rpm module with a built in rev limiter that you can dail from 5,000 to 10,000 rpm's. It's a new one too. My timing is set 36 degrees before top dead center. No I am not running a vac advance can. I have my distributor lock out on the vacuum advance and no springs and weights. It stays at 36 degrees all the time. I bought a new Keith Dorton Circle Track carb. Changed the jets from a 73 to a 78 and pv from a 3.5 to a 9.5. The carb worked good on dyno but started having fuel pump problems. So, I bought a new Holly 6 1/2 to 8 psi pump. Got the carb from Smiley's Racing Parts.
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Old 03-21-2012, 02:29 PM
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Originally Posted by hpete
The last time I watched sportmods race they were ALL popping about halfway down the chute. The stock cars were doing the same thing. This was in hot laps and heat races. By the time they ran the features the track was shiny and black and no more popping. I assumed it was the rev limiters causing the popping.
Last friday the track went dry too but, still was popping and now it's slightly popping about 2,500 rpm's.
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Old 03-22-2012, 12:36 AM
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ok now just try this out.....you might hate it but it worked for me. i had a major popping sound in my side pipes of my vette. im running a 383 with a .510 cam......... my spark plugs were gap at .45 just like yours. i lowered it to .35 and the popping went away. its easy to do and if it doesnt work write back and call me an idiot LOL !!!
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Old 03-22-2012, 07:43 AM
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Quote:
Originally Posted by OMARS67
ok now just try this out.....you might hate it but it worked for me. i had a major popping sound in my side pipes of my vette. im running a 383 with a .510 cam......... my spark plugs were gap at .45 just like yours. i lowered it to .35 and the popping went away. its easy to do and if it doesnt work write back and call me an idiot LOL !!!
why did you move up to a 9.5" PV? Do you monitor the AF mixture at all right before, during, and after the pops?
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Old 03-22-2012, 09:10 AM
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Originally Posted by OMARS67
ok now just try this out.....you might hate it but it worked for me. i had a major popping sound in my side pipes of my vette. im running a 383 with a .510 cam......... my spark plugs were gap at .45 just like yours. i lowered it to .35 and the popping went away. its easy to do and if it doesnt work write back and call me an idiot LOL !!!
Thanks for the info I will try that and let you know if it works.
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Old 03-22-2012, 09:20 AM
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Originally Posted by ap72
why did you move up to a 9.5" PV? Do you monitor the AF mixture at all right before, during, and after the pops?
I read the instructions that came with the Holly carb and it said to check and see how much vacuum the motor is pulling and divide that by 2 to get the right pv. My motor is pulling 20 inches of vacuum.
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Old 03-22-2012, 09:50 AM
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Originally Posted by leonmcbee53
I read the instructions that came with the Holly carb and it said to check and see how much vacuum the motor is pulling and divide that by 2 to get the right pv. My motor is pulling 20 inches of vacuum.
20" at idle?! Something is definitely wrong there, the cam you have should not be making 20" at idle- furthermore that holley recommendation isn't worth **** when it comes to racing, that's for street vehicles. put the 3.5" power valve back in there.

When you had this engine on the dyno, I assume you dialed in the timing for peak power, on the carb, did you change the PVCR's or the bleeds or just the jets?
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