I have a '69 Mach 1 With a 351W I recently put in a MSD6A ignition box and Pro Billet Dist. I've been through all the tuning advice and through thier (MSD"s) Forum and they can't seem to help me. I'm getting a backfire through the carb.when I punch the throttle. It doesn't change with a timing change but the odd thing I've found is that when I pull any of the plug wires #3, #4, #5, or #7 the idle doesn't change. They are not firing. Now that seems odd to me with them not being on the same plane on the stock intake, and I just rebuilt the Edelbrock carb #1407 750CFM. which is plenty for this engine so It can't be a lean condition. If you can fix this with your advice I'll buy you a beer. I'm that desperate.
firing problem
- Thread starter redneckjeff
- Start date
A carb's cfm rating has absolutely nothing to do with a "lean or rich" condition. If it backfires thru the carb when you punch it, that tells me it is a lean condition. The accellerator pump circuit isn't working correctly.
You do not understand how a carb works, get a manual and read up on them.
I cannot tell you how to fix the problem as you have an Edelbrock carb (I'm a Holley guy) but the prolem is a lean condition. One of the resident Edelbrock carb guys will have to tell you how to fix it.
Come on guys, help him out................
You do not understand how a carb works, get a manual and read up on them. I cannot tell you how to fix the problem as you have an Edelbrock carb (I'm a Holley guy) but the prolem is a lean condition. One of the resident Edelbrock carb guys will have to tell you how to fix it. Come on guys, help him out................
NO, if you have 4 cylinders that are not firing, then your motor would be running rich. and dumping the unburned fuel out thru the exhaust. I didn't accuse you of anything. I simply informed you that you obviously didn't understand a carb by your statement that it was overly rich due to the carb being too big for the application.
I don't think the ignition would be the problem, he says numbers 3, 7, 4 & 5 aren't firing. If the box was set to 4 cylinder, that wouldn't happen. 3 & 7 fire consecutively as do 4 & 5 . And it would hardly run on 4 cylinders with two sets in the sequence out of the picture.
You talking to me or redneckjeff ? If yer talking to me then I owe you more then 1 beer. You ever make it out to California/LA area and I'll take you out for some beers. All the trouble you've saved me/got me out of its the least I could do =-)
Naw, I was talking to redneckjeff, he's supiciously silent now about his ignition (carb )problem. I gave it more thought and a backfire will also result from retarded igniton timing but I see that he said he tried adjusting that already. His so called not firing cylinders are caused by the lean condition. It's too easy to check the firing of each, all that's needed there is to check for spark. I think too many guys who are new to carbs think that somehow a carb pumps fuel into the engine like fuel injection, hence the mind thought that bigger is better when it comes to choosing carbs. And also the popular misconception that if one is too big or small, all that's needed it is to "jet it up" or "jet it down" to correct it. Maybe I did come off too strong in my first reply, but his statement that the carb was "more than enough, so it can't be lean", set me off on a tangent. It just showed me that he didn't understand that a carb problem and an ignition problem can make the same end results and can be confused with one another.
Found the problem.
I guess you could say the problem lies with my brother, Who I bought the car from 4 years ago. He never knew that the cam had been replaced with a 302 cam. Even though he owned it for 18 years. He's not mechanically inclined. I switched the firing order and knew as soon as I fired it up that that was the problem... Not a lean condition. So if anyone is getting the beer it would be Max Power. Thank you for your help and if any of you are up here in the Portland OR area I'll buy all of you a beer. Jeff
I guess you could say the problem lies with my brother, Who I bought the car from 4 years ago. He never knew that the cam had been replaced with a 302 cam. Even though he owned it for 18 years. He's not mechanically inclined. I switched the firing order and knew as soon as I fired it up that that was the problem... Not a lean condition. So if anyone is getting the beer it would be Max Power. Thank you for your help and if any of you are up here in the Portland OR area I'll buy all of you a beer. Jeff
HookandLadder
Founding Member
Glad you got it fixed. I was gonna say the firing order was wrong. Went from a 302 to a 351 grind and forgot to reset the order and had the same problem. It'll run....just not in gear or long.
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