Backfiring
You are not currently logged in. Login to myAccount   Forgot Your Login?   SignUp For a Free Account
 
Buy TShirts & DVDs!-Sell Your StreetRod FAST!-Help-Contact Us
Quick Search:
Backfiring
Posted: August 23 2005 06:14 PM
 
Steve Weinberg (aka maniac) [ View ] [ Email ] [ Car Ads ] [ Blogs ]
Bethel, Connecticutt
 
Well we changed an intake on my buddy's small block Chevy and now have a backfiring problem

Took off an old Torker and put on a new Performer air-gap.

Everything else is the same, now it backfires out the exhaust with the vacuum advance connected, BUT it runs fine with the vacuum advance disconnected. Timing is 8 degrees BTDC with a 38 total.

It's a 327 chev with an MSD Dist and 6-A box, 600 Holley.

No vacuum leaks, that I can tell, dist. in correctly and plug wires on correctly, plugs are new.

Any ideas???? WE are stumped right now.

 
 
Comments
 
Posted by maniac  -  08/21/2005 06:12 PM
I know, we had the dist out 5 or 6 times already, put it on TDC and put it back, it's driving us NUTS, and were runnin out of beer, NO beer sales on Sunday here :-(
maniac [ View ] [ Email ] [ Blogs ] [ Car Ads ] Bethel, Connecticutt
 
Posted by flaminford34  -  08/21/2005 06:46 PM

Is the rotor lined up with the proper spark plug wire after the dist. is seated?
flaminford34 [ View ] [ Email ] [ Blogs ] [ Car Ads ] The Villages, Florida
 
Posted by maniac  -  08/21/2005 06:50 PM
Yep rotor lines up, like I said it runs GREAT only if the vacuum advance is disconnected.
maniac [ View ] [ Email ] [ Blogs ] [ Car Ads ] Bethel, Connecticutt
 
Posted by Crazyhorse Rod Shop  -  08/21/2005 04:35 PM
try 6 degrees
dont poke the porchdog........he bites [ View ] [ Email ] [ Blogs ] [ Car Ads ] BLUFF DALE, Texas Charter Member since March 2003
 
Posted by brianangus  -  08/22/2005 08:01 AM
This is really a wild hare, but is the performer manifold new or used? If you pull the manifold to reseal the gaskets, get a straight edge (like a good carpenters square) and check the mating surfaces of the manifold for flatness.----used manifolds have been known to warp due to uneven bolt tightneing or undue engine heat.-----Hell, even if its new, check it for flatness.
brianangus [ View ] [ Email ] [ Blogs ] [ Car Ads ] Barrie, Canada
 
Posted by JAWS  -  08/22/2005 09:01 AM
All the vacuum advance was for was to add more timing at idle/ lower rpms to make up for low compression and for emissions. Sounds to me like the advance unit may be adding to much advance(backfire through exhaust is advanced-retarded backfires through the intake) for your wngine combo. If your advance is a 10 degree then you have 18 degrees at idle and 48 degrees total if you are not under severe load, under load the advance drops off due to lack of vacuum. I dont run vacuum advance units with a performance dist/ignitions/engine combos. I set the initial timing at around 12 and total around 38. The old torquer was designed to flow fuel/air at mid to higher rpms and the performer is a dual plane shallow intake that brings the mix faster at lower rpms. I imagine that before you were fairly lean at lower rpms before and the timing setup would have been disguised. With the more fuel sooner your timing is showing up cause there is ample fuel to burn. I bet your exhaust is hotter now than before at the lower r's too. Just a thought.-Brant
An electrical headache can make a great car a pain [ View ] [ Email ] [ Blogs ] [ Car Ads ] Boise, Idaho Charter Member since August 2004
 
Posted by brianangus  -  08/21/2005 04:29 PM
Throw a timing light on it and see if the timing mark is where it should be---I know from experience that they will run with distributor out by one tooth on the gear mesh.
brianangus [ View ] [ Email ] [ Blogs ] [ Car Ads ] Barrie, Canada
 
Posted by Crazyhorse Rod Shop  -  08/22/2005 08:32 AM
i would retork the intake before i tore it down. a vac leak would show up in the idle. you can pull plug wire one at a time to see if you can find the runner leaking. make real sure your carb gasket is sealing the carb good. there are a lot of gaskets that dont work on the 600. i ran into this once before. check exhaust temps to see if there is a hot one. good luck.
dont poke the porchdog........he bites [ View ] [ Email ] [ Blogs ] [ Car Ads ] BLUFF DALE, Texas Charter Member since March 2003
 
Posted by Crazyhorse Rod Shop  -  08/21/2005 04:48 PM
many times i have to just start over and make sure i have everything right.
dont poke the porchdog........he bites [ View ] [ Email ] [ Blogs ] [ Car Ads ] BLUFF DALE, Texas Charter Member since March 2003
 
Posted by maniac  -  08/21/2005 04:42 PM
The timing mark is right on, we tried moving the dist either way and it still backfires, only time it runs right is with the vacuum advance disconnected, and we are running the vacuum line on the "ported" side.
maniac [ View ] [ Email ] [ Blogs ] [ Car Ads ] Bethel, Connecticutt
 
Posted by Red's Place Custom & Restoration  -  08/21/2005 07:40 PM
take a long shot and try and change the vaccum advance and you know that sometimes you could get a bad sparkplug out of the box. They do get dropped sometime had it happen to me drove me nuts.
Red's Place Custom & Restoration [ View ] [ Email ] [ Blogs ] [ Car Ads ] Charlotte, North Carolina
 
Posted by brianangus  -  08/22/2005 07:57 AM
The only thing left is a vacuum leak. Pull the intake and reseal the gaskets, particularly the front and rear with a ton of blue Permatex.
brianangus [ View ] [ Email ] [ Blogs ] [ Car Ads ] Barrie, Canada
 
Posted by Crazyhorse Rod Shop  -  08/21/2005 06:48 PM
move!
dont poke the porchdog........he bites [ View ] [ Email ] [ Blogs ] [ Car Ads ] BLUFF DALE, Texas Charter Member since March 2003
 
Posted by bigdude  -  08/21/2005 07:45 PM



Spray some Shine wd -40 around the top of the intake and watch the exaust,you might have a slight air leak.
resident know it all [ View ] [ Email ] [ Blogs ] [ Car Ads ] Three Rivers, Michigan Charter Member since January 2004
 
Posted by Crazyhorse Rod Shop  -  08/22/2005 03:37 PM
we take'm out back an shoot'em if they dont act right.
dont poke the porchdog........he bites [ View ] [ Email ] [ Blogs ] [ Car Ads ] BLUFF DALE, Texas Charter Member since March 2003
 
Posted by hotrodfreak  -  08/22/2005 10:04 PM
Jus a thougt, I heard of a intake coming out of the box with a drilled and threaded bolt hole with no bottom- caused a major vacuum leak only on a couple of cyls. Ran ok except for acackle like backfire in the exaust {so i was told]
hotrodfreak [ View ] [ Email ] [ Blogs ] [ Car Ads ] hancocks bridge, New Jersey
 
Posted by maniac  -  08/22/2005 03:35 PM
Well we spryed WD-40 all around the intake and got no change in idle, so I'm pretty sure there is no vacuum leak, also sprayed the carb too.

Its a new manifold, I'm thinking its in the distributor.

I think we will try another one and see what happens.

Thanks fo all the help and I'll post what we find.

maniac [ View ] [ Email ] [ Blogs ] [ Car Ads ] Bethel, Connecticutt
 
Posted by maniac  -  08/22/2005 05:42 PM
NO crosfire cap, had enough of that crap years ago, notice it isnt even around anymore?

Wires all on correctly, checked em a dozen times, only backfires with vacuum advance connected. I'm still leaning to the distributor.

maniac [ View ] [ Email ] [ Blogs ] [ Car Ads ] Bethel, Connecticutt
 
Posted by hotrodfreak  -  08/22/2005 10:07 PM

I had a buddy put similar stuff on a camaro once and ran lousy, eventually we found he hooked up the coil backwards
hotrodfreak [ View ] [ Email ] [ Blogs ] [ Car Ads ] hancocks bridge, New Jersey
 
Posted by hotrodfreak  -  08/22/2005 10:09 PM

Did you ever watch it run in darkness - to see for spark jumpin somewhere?
hotrodfreak [ View ] [ Email ] [ Blogs ] [ Car Ads ] hancocks bridge, New Jersey
 
Posted by Willys33  -  08/22/2005 04:48 PM
Backfiring can only be caused by ignition of unburned fuel after it leaves the cyclinder or while the intake or exhaust is open and the plug fires. You have taken out the distributor to replace the intake and my guess would be that you have two wires crossed (can't have just one!!!). You may have the wires in the correct location BUT unknown to you it has a Crossfire cap. Check it again.
Get off the trailer and drive [ View ] [ Email ] [ Blogs ] [ Car Ads ] Alamogordo, New Mexico
 
Posted by 55plumcrazy  -  08/23/2005 06:14 PM
assuming that your valves are not to tight, let me get my two cents in, it sounds like a dist. problem but try this,measure around harmonic balancer from timing mark back to timing mark,example if its 25' divide that number by 10 answer would be 2.5' now ,exactly 2.5' from your old mark make your new timing mark. set your timing at 4' retarted @ 3000 rpm,s which is 34 ' don't worry about cranking, it will start fine. most small blocks run best at 34' big blocks 32' domed pistons with racing fuel can stand 38' what the hell........ plumcrazy ps do that with vac. adv. unplugged..
55plumcrazy [ View ] [ Email ] [ Blogs ] [ Car Ads ] wilmington, North Carolina
 
Posted by Crazyhorse Rod Shop  -  08/23/2005 06:53 AM
i think your advancing so far your firing 2 at once. possibly a bad cap or wire.anyway you look at it your firing one at the wrong time. msd boxes will put on a light show. great for racing but a real pain sometimes.
dont poke the porchdog........he bites [ View ] [ Email ] [ Blogs ] [ Car Ads ] BLUFF DALE, Texas Charter Member since March 2003
 
Back To Top
Please Login or Register to Comment
Existing Member? Sign In.
New Visitor? Click Here to Get Started!
 
Existing Member but forgot your Login Information? Click Here.