Backfire !@#$ Help please.
Thread Starter
Instructor
Joined: Nov 2005
Posts: 243
Likes: 0
From: KC Kansas
Backfire !@#$ Help please.
Ok so only after its warmed up. Only on pass side. Only between 2k and 4k RPM. Only under load, like when im going up a slight incline slowly pulling only 2500 rpm and have it held there I can hear the backfire although its slight. Its alot louder at higher rpm like the 4k range. Im stumped. 
Any suggestions?
I run side pipes so I know its on the pass side.
Any suggestions? I run side pipes so I know its on the pass side.
Melting Slicks
Joined: Nov 2001
Posts: 2,668
Likes: 43
From: Eastern US XX
Ok so only after its warmed up. Only on pass side. Only between 2k and 4k RPM. Only under load, like when im going up a slight incline slowly pulling only 2500 rpm and have it held there I can hear the backfire although its slight. Its alot louder at higher rpm like the 4k range. Im stumped. Any suggestions?
I run side pipes so I know its on the pass side.
Any suggestions? I run side pipes so I know its on the pass side.
Drifting
Joined: Sep 2007
Posts: 1,572
Likes: 51
From: Wichita Kansas
If all of your ign is in order; timing, fireing order, plugs, vac advance ect., then it sounds like you need to adjust the rockers.
Racer
Joined: Aug 2006
Posts: 330
Likes: 3
From: Wellington, New Zealand
I had the same problem with my 74, it wasn't constant but normally happened under load. I tried the old trick of jetting water down the carb with the engine running at about 2,000 rpm this cleaned off the valves and the combustion chamber of carbon and crud the car ran like a Swiss watch after that. Its an old trick but it really works, other guys here use a product called sea foam to do it, we don't get sea foam in NZ so I just used water. Its worth a try and won't harm your engine.
Melting Slicks
Joined: Nov 2000
Posts: 2,738
Likes: 53
From: Bogart GA
You may be running to lean. I don't know what carb you are running but see if you get a lean "pop" and/or hesitation when you accel from a cruising condition. Check the color of your plugs. If there is a dyno facility near you, have them hook you up the their wide band O2 analyzer to see your fuel curve throughout the rpm range. I suggest that to anyone. Best 50 bucks you can spend.
Instructor
Joined: Sep 2005
Posts: 241
Likes: 0
From: St Louis Missouri
Have you looked at your #4 spark plug wire? I know that it can be tricky to get the wire on the plug well because of how close the headers are to that plug. If it’s not on all the way it will cause a backfire through the passenger pipe.
Thread Starter
Instructor
Joined: Nov 2005
Posts: 243
Likes: 0
From: KC Kansas
Awesome, great suggestions guys, thanks. I will try all of them this weekend. I will do the compression test first, then valve check, then the water/sea foam test at 2000 rpm, then the lean test. I have a wide band sensor on order but havent gotten it yet. Also that #4 plug wire is a pain in the *** so I will double check it, I know it was a pain getting it on there.
I will give an update tomorrow or Sat eve incase none of this fixes my problem. I hope it does. Thanks everyone.
I will give an update tomorrow or Sat eve incase none of this fixes my problem. I hope it does. Thanks everyone.
Last edited by 79VetOwner; Nov 15, 2007 at 06:53 PM.
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