New exhaust - now have backfire - The 1947 - Present Chevrolet & GMC Truck Message Board Network

PHOENIX · 10-13-2004, 06:56 PM

I put on new headers, new y-pipe, new cat and new muffler (aero chamber).
From y-pipe back its a single 3" pipe all the way out. Cat is in stock location, muffler is about 1'-6" in front of rear axle, pipe goes over rear axle and out behind drivers tire like stock.

When I rev it up like 3000 rpm + and let off the throttle there is a few back fires right before it returns to idle speed. What causes this?
Is this carb settings, timing issue or is this what I should expect with this higher flowing exhaust setup?

I will try to get a video or sound clip up later to show you what I am talking about.

Thanks!

Tom · 10-13-2004, 10:27 PM

Better flow = leaner mixture. Play with the carb a little and you should be fine. I know short exausts like mine [exit before rear wheels] can cause some poping but yours wont.

PHOENIX · 10-15-2004, 01:51 AM

I definately need to adjust the carb.

I am pretty sure I found the problem.
These headers have the air tubes and I have brand new air pump check valves installed. But not the hoses from the air pump diverter valve to the check valves. I need to buy new hoses that is why they are not on. Well I was wondering about it, so I put a cap on each valves and rev'd up the truck. No more popping sound at all. Sounds pretty good too, I might drive it to work tomorrow, but I dont know cause my tags expired. I have to go to emissions

The reason I didnt suspect this at first is because the check valves were not allowing any outward flow. Now they they are letting out a very slight amount. Not enough to over power the air being pumped in from the smog pump though.

Mike76251 · 10-16-2004, 09:46 AM

I think you have it nailed.
Most check valves do leak a little and it doesn't take much leakage to hear it rather loudly.
Not that I would know about smog pumps and divertor valves and cats and emission testing and things like that

.

cliffsta · 10-16-2004, 11:17 AM

Quote:

Originally Posted by Mike76251

Not that I would know about smog pumps and divertor valves and cats and emission testing and things like that

.

LOL, my dad said he disconnected all that smog stuff (except the cat) ages ago. Most places around here don't even look for a cat.

10-13-2004, 06:56 PM	#1
PHOENIX Registered User Join Date: Oct 2002 Location: Phoenix, Arizona Posts: 4,703	New exhaust - now have backfire I put on new headers, new y-pipe, new cat and new muffler (aero chamber). From y-pipe back its a single 3" pipe all the way out. Cat is in stock location, muffler is about 1'-6" in front of rear axle, pipe goes over rear axle and out behind drivers tire like stock. When I rev it up like 3000 rpm + and let off the throttle there is a few back fires right before it returns to idle speed. What causes this? Is this carb settings, timing issue or is this what I should expect with this higher flowing exhaust setup? I will try to get a video or sound clip up later to show you what I am talking about. Thanks! __________________ * AVOID: LOPER'S PERMORANCE / LOPERSPEED.COM OF PHOENIX, AZ & COTTMAN TRANSMISSION *

10-13-2004, 10:27 PM	#2
Tom driving is in my blood Join Date: Dec 1999 Location: Mesa AZ Posts: 5,748	Better flow = leaner mixture. Play with the carb a little and you should be fine. I know short exausts like mine [exit before rear wheels] can cause some poping but yours wont. __________________ -78 c10 short/step: 388cid, M20, 5/5 drop, lots more. Playtoy and first vehicle. -98 c1500 x-cab: 5.7L, 17" rims, 5/6 drop, flowmaster, helper bags,NBS rear disk brakes. -02 Suburban 4x4: leveled front -CBR600F4i, CBR600RR, CBR1000RR, and standup skis DISCLAIMER: I cant spell for the life of me.

10-15-2004, 01:51 AM	#3
PHOENIX Registered User Join Date: Oct 2002 Location: Phoenix, Arizona Posts: 4,703	I definately need to adjust the carb. I am pretty sure I found the problem. These headers have the air tubes and I have brand new air pump check valves installed. But not the hoses from the air pump diverter valve to the check valves. I need to buy new hoses that is why they are not on. Well I was wondering about it, so I put a cap on each valves and rev'd up the truck. No more popping sound at all. Sounds pretty good too, I might drive it to work tomorrow, but I dont know cause my tags expired. I have to go to emissions The reason I didnt suspect this at first is because the check valves were not allowing any outward flow. Now they they are letting out a very slight amount. Not enough to over power the air being pumped in from the smog pump though. __________________ * AVOID: LOPER'S PERMORANCE / LOPERSPEED.COM OF PHOENIX, AZ & COTTMAN TRANSMISSION * Last edited by PHOENIX; 10-15-2004 at 01:53 AM.

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10-16-2004, 09:46 AM	#4
Mike76251 Senior Member Join Date: Mar 2003 Posts: 2,499	I think you have it nailed. Most check valves do leak a little and it doesn't take much leakage to hear it rather loudly. Not that I would know about smog pumps and divertor valves and cats and emission testing and things like that .



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