My nova keeps backfiring

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hey there. This is my first of many problems I'm going to need you guys to help me out with. My nova keeps backfiring and its annoying the hell out of me. Here's some info that might help you help me... I have a '72 nova with a 350 (put in 4 days ago, bored .60 over) and it has a 4-speed muncie. It only backfires when I gun it and when I downshift and/or coasting to a stop. I believe it's a timing issue, but I could be wrong...that's why I'm here. The firing order is correct, however, I was told that the #1 cylinder should be on the 11 o'clock position on the distibutor cap, but it's on the 5 o'clock position on my distributor. Does this matter? Please help.
-Mike

posted by  mikeymike2946

If the #1 wire tower should be on the 11 oclock position, and it's on the 5 oclock position, then it's obviously indexed wrong. Pull the distributor, rotate, put it back in. Set timing and get back to us...

posted by  DodgeRida67

I changed the wires around so the #1 cylinder is in the 11 o'clock position... the car would turn over but wouldn't catch. I've read several postings on other sites saying that the #1 cylinder should be in the 5 o'clock position, but I have read some that say it should be in the 11 o'clock position as well. My car and only starts in the 5 o'clock position, so I don't think the position of the spark plug wires on the distributor has anything to do with it. My timing was adjusted with the help of a timing gun... still backfired, although, not as bad. I was told that my cam could have an advance on it, how would I adjust my timing to make up for this? This is the only problem I can think of. Thanks.

-Mike

posted by  mikeymike2946

Don't think he understood. You might want to explain a little more in depth as to re-positioning of the distributor.

posted by  lectroid

I repositioned the distributor so that the #1 cylinder is in the 11 o'clock position. My car turns over but doesn't catch. I checked everything atleast 5 times and I still didn't have any luck. I found a post in another forum that says the only thing that matters is that the #1 cylinder plug wire is connected to where the rotor is pointing. It doesn't matter if it's 5 or 11 o'clock. Has anybody heard of this?Thanks

-Mike

posted by  mikeymike2946

Here's the deal... after adjusting the distributor and spark plug wires to what everybody recommended my car didn't want to start. I re-adjusted it to the way it was originally and it started up just fine although it was still backfiring. I adjusted the timing and I messed with the carb a little bit, it doesn't backfire anymore but there is some pinging in the exhaust when I let off the accelerator and every once in a while at light acceleration. I'm guessing its due to the air/fuel ratio being to rich. Does anyboby have any other ideas of why it's doing this? Thanks

-Mike

posted by  mikeymike2946

does it "ping" under a heavy load too or just under light acceleration???

if you hear "pinging" under a heavy load, either your timing is too far advanced or you're not using a high enough octane fuel.

Is the motor in question a performance engine or a stock 350 bored over?

posted by  Sick88Tbird

Mike,back to basics.A few things could be going on.First,recheck your firing order.Pull timimg again.I'd use 8 degrees as a baseline.Do a plug check.Black and sooty?or white and chalky.What does the exhaust look like when you hammer on it?Have you rechecked the valve lash(valve too tight)Is the motor fresh,or a cutout?

posted by  TurtlePimp

sick88tbird- it only pings when i'm coasting. if i let off the gas after light acceleration it doesnt ping that often, its after heavy acceleration when it really does it. i use 93 octane in it so i dont think the fuel has anything to do w/ it. i'll have to re-check the timing. as far as the engine, i believe its a performance engine.

turtlepimp- i havent checked the plugs yet, i was planning on doing that tomorrow afternoon. after i punch it, i cant see any exhaust. my car started to backfire after i had some head work done (i had the rocker arm studs pinned onto the heads because they were coming loose). i dont know if the valves were messed w/ at all. how would i check for valve backlash? and what do you mean is the motor fresh or a cutout?

while trying to fix the backfiring problem i encountered another problem. my engine now bogs at high rpms. by bog i mean that it tries to go but it starts to sputter. after a minute or two of this it'll eventually die on me, and i'll have to wait 3-5 minutes to start it up again. if someone can explain to me why it does this and a couple of solutions to this problem i would really appreciate it.

posted by  mikeymike2946

I'm not realy an expert on non EFI engines but it sounds like a problem i had in my 96 Grand AM. It had an ocasional ping and bogged down at high rpms. After stalling on the interstate. I towed it to a dealer putting in on the computer i found out the Primary O2 sensor was going bad, in turn effecting the EFI unit. In this event it would say there was not enough exaust and would flood the engine with fuel. The exaust had a slight sulfur smell to it also. I run 101 off the pump.

Also you might call the people that sold/fixxed your engine and tell them that you are haveing problems and need help. Offer beer usualy works...just kidding. Most people will help or might have advice to help you out they might of had the same problem before or it might be a small defect. You realy shouldn't be stressing you engine until you break it in the rings and valves they are still seating.

You siad that you had you the rocker arms pinned because they kept comming loose you should invetigate on the "why were they coming loose". I can't realy tell you without loking at it.

I'm a newer engine type a guy. One thing i do know is that when you time it just make sure that that the first cylinder in the firing order is at top-dead-center and go from there, it can mess up you timing up just enough. With a distributer the points are set to spark at a set degree 4 cyl 90/6cyl 60/8cyl 45 degrees. So in theory find TDC and put the distributer cap in with the arm on cyl one. You can get it very close and can make fine adlustments from there. It could also be advancing to much so when you let off the throttle it fires to late or can't burn all the fuel fast enough. Using the light gun have someone help you. Have them rev the engine for a few seconds and see where it advances to. I don't know the degrees of advance though. Then see how the timing reacts during deceleration. Could be a vacuum or diaphram issue. The spark plugs will tell you alot. Like i said i'm not an expert, just things to try.

Remember make one adjustment at a time to isolate the problem.

posted by  decap66

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